early 944 brakes, stock MC....dosent feel right [Archive]

super vw

July 17th 2004, 22:53

Well i got all my plumbing done for my 1303 project, i have early (single piston) 944 brakes on all four corners and i am using my stock master cylinder for now... i already have it mounted so i thought i would see if it would work.

I dont think its going to cut it, the pedal has a fair amount of travel till it engages the brakes, but if you push on it REAL hard it almost hits the bulkhead. kinda soft/squishy feeling, not firm like on our 73 Thing.

I have not driven the car or rolled it yet becuase their is no motor, no running gear..ect so i cant say if they work ok or not. but my the feeling of them now, i dont think they would.

So the question is what next to try, i cant be spending a lot or money trying everything out there. so what is a proven MC to use with this setup?

I have heard to use the 944 unit (but it originaly had a Servo/Booster) and to use an early 911 unit (no booster correct?)
Anyway i look at it, i cant use a booster, no room, and most importantly, i dont want to deal with mounting one up at this point, im sure it would involve a lot of fab and hacking to make one work.

So what to use, somthing that has been used... not just a sugestion on what may work... somthing proven to work.

Thanks!
Jonathan

LOAF

July 17th 2004, 23:15

Super VW

Great question, would like to hear what people will say.. I am in a similiar boat.. Not too long ago at a swap picked up a new VW M/S for my 1303 but I had the same suspisions..

Some folks have used 911 and 944 but not sure how.. not yet there.. but I believe there may have been some bias issues..

Be patient and some folks who are a little ahead of us will respond..

ALex

zen

July 18th 2004, 09:59

i am running 951 brakes with a 944 M/C, so i can't speak with authority, but i think there are more than a few guys running 944NA brakes with a stock M/C. and you are sure they are fully bled right?

boygenius

July 18th 2004, 12:28

I am with Zen, double check that ALL the air is out of the system.

You have a super correct with the 944 spindle/hub/caliper swap via a kersher ball joint.

Did you have good brakes before you did the swap.

Are you using new (newer) rubber/stainless brake lines. One of mine had a tiny pin hole in it and it drove me crazy because I could never get a firm pedal but when I would look under the car I couldn't find a drip untill I finally replaced the lines and when I bent one of the lined I could see a little crack with brake fluid seeping out of it.

Check that you still have the required clearence between the brake pushrod and the master cylinder. If thre is no clearence the fluid won't return properly and you will never get the air out.

Make sure ALL of your fittings are tight. Double check them. If they are a little loose the fluid realy won't leak out but when you release the pedal air will be sucked into the line.

Hope that helped...

super vw

July 18th 2004, 14:00

Now that you mention it, there MIGHT be some air in the system still. i went and applied the brakes this morning and could here a slight squish of air near the MC. so i think your right... i need become a killer and let this sucker bleed :D

i have not noticed any leaks of fluid, but when i was using a hand held bleeder deal that sucks the fluid/air out it would let some fluid out but more air than fluid. then all of a sudden it would just drop in pressure and suck only air. But when we went to try bleeding it the manual way (one person pumps, one opens valve...) their was only fluid coming out maybe tricking us that we had it fully bleed...

So i will give it another try today and see what happens.

Thanks, ill tell ya how it goes.

Jonathan

boygenius

July 18th 2004, 14:06

Sometimes the vaccum bleeders will suck air from around the fitting on the caliper. The rubber cap from the vaccum pump hose that goes over the bleeder should fit tightly, if not it will suck a little air from around the fitting. I would still double check the tightness of your fittings. Good luck.

Jeza

July 18th 2004, 19:32

I'm also in a similar boat.

944 single piston calipers all around and a stock bug 19.06mm master cylinder.

I also have a fair amount of pedal travel and quite a bit of squish. It does get firmer with some pumping but I'm pretty sure I've got the air out of there. I'm not getting any air when the calipers are bled, unless it's hiding elsewhere.

I've been suggested to check out shimming down the front pistons instead of using the 944 mc. The reason behind this is that the 944 is a front engined car and the brake balance will be set up as such.

I reckon if the front calipers are approx 44mm diameter the front to rear ratio will be about right, and similar to the CB kits, just bigger and vented.

Do the 4 pot calipers have less volume / fluid area? The 4 pistons make them more efficient. This may effect the pedal feel.

Hopefully this sparks some thoughts

Cheers
Jeremy

Jeza

July 18th 2004, 23:20

Okay a quick ask around brake shops at lunch yielded no results- so perhaps my comment about shimming / sleeving the front calipers was barking up the wrong tree.....

Any comments

Cheers
Jeremy

ricola

July 19th 2004, 03:48

Jeza

July 19th 2004, 05:05

Rich

Thanks for the comments. I agree with you, the stock 19mm (Bug) master cylinder just doesn't have enough volume for the huge front calipers. I also wonder if it gives too much mechanical advantage / leverage allowing you to flex the front caliper (single pots are flexier than the 4 pot cousins), hence the spongy feel.

I think I will fit the 944 master cylinder, its front to rear ratio (having actually done the calculation now) isn't as bad as I suspected it would be.

Did you have any difficulties fitting the 944 master cylinder Rich? From memory people have said it bolts on, requires a tee piece to be used for the brake light switch, and use the remote "plugs" in place of the reservoir.

Cheers
Jeremy

ricola

July 20th 2004, 04:27

Was an eaasy fitment, just requires bolts with nuts as it isn't threaded like the steel bug m/c. Just a bit of bending of the hard lines and the switch fitted in a T. If I remember correctly, one of the front connections was very close to the tunnel side so it would be easier to fit that one before you tighten it all up fully to give you some movement.
Rich

Jeza

July 22nd 2004, 05:56

Rich and anyone else how has fitted a 944 MC to a beetle / aircooled VW.

How did you get around dealing with the remote reservoir. I thought it was just a case of using the VW fittings in the 944 MC, but the 944 rubber bungs ID is too big and the rubber bungs from the VW OD is too small for the 944 MC.

Is it just a case of fitting new rubber bungs?

Cheers
Jeremy

Jeza

July 23rd 2004, 06:50

Right everybody I've found the answer.

It turns out that orignial German MC's have small diameter plastic connector fittings and small rubber bungs.

After market ones have larger ones that are the same size as the ones used for the 944 MC.

These people have both:
Small
http://www.bughaus.com/master_cylinder_connecting_pipe_-_113611153.htm

and large
http://www.bughaus.com/master_cylinder_connecting_pipe_-_113611153C.htm

And an image of the large connecting pipe, that I believe will fit the rubber bungs on the 944 mc once the reservoir is removed.

Cheers all
Jeremy

super vw

July 23rd 2004, 12:06

cool, i have a new MC (1303 unit) but i think its aftermarket SO i might be in luck when i got with a 944 MC.

So you have the 944 MC in hand correct?
When you get it all working, tell us how it works!

BTW whats the part number of the 944 MC you have?

Thanks !!

Jonathan

Jeza

July 24th 2004, 02:46

Jonathan

Not sure what the part number is - there aren't any part number like numbers that I can see on it. But it is the "ate" item.

I'll let you know when its in with the results.

At the moment I'm planning to separate out the front lines (there is 2 front line ports in the 944 mc). I'll use a plug in one side of the front T piece and run one new front line to one side and adjust the old front line to the other side.

The rear is lengthed with a T piece to use the pressure brake light switch and a short line to the new mc port - same as every one else.

Also an update on the plastic remote reservoir fittings. I had a lot of trouble tracking these down. None of the brake shops could help. I eventually found some in an old big BMW (7 series? from 70's?) at pick a part. So if you end up stuck then try the BMW parts department.

Cheers
Jeremy

Wally

August 2nd 2004, 16:39

I'll add my experience...

I started off doing the rear brakes first as there was a delay on sorting my front bearing adapters. Using the bug m/c, that was the best combination by far so I should have just drilled the front discs to Porsche pattern.

I agree!

The bug m/c has not got enough displacement for the single pot front calipers no matter how much bleeding you do.
Rich
Thats not my experience...
I still use the stock m/c on my 1303 with 944 Turbo Cup brakes front and rear. The Cup brakes are even larger than the stock turbo ones, but I have a very hard pedal; can easily lock front brakes, but bias sucks! The back should give more brake action, so I'am not sure what the best way is. Mounting a m/c with even more travel up front certainly is not (for my car that is). Maybe a 23/23 m/c which can be squeezed in the front lines or s/th like that.
Because of the rear engine and 'reverse' weight distribution of the bug compared to a front engined/watercooled car, mounting the same m/c seems pointless to me. Fitting a m/c with 21/19 cups rear/front would make more sense to me...

I also have the 944 N/A brakes on my squareback now and, as with the bug, the pedal got harder after the swap! Logical, cause the drum brake always needs more travel to get to the drum, after which the spring retracts it.

I suspect, m/c diameters front/rear are just used to also get the required balance from the factory. The displaced volume when breaking may just be so little (with good seating, well broken-in pads), that 19 or 21 mm may not make a noticeble difference in that aspect.
Really, really make sure your pads are broken in properly before you judge any 'sponginess' you may think you encounter. Usually our bugs are not driven that much nowadays, so judging too soon the pedal feel is an easy mistake, I suppose.

Good luck all,
Walter

ricola

August 3rd 2004, 04:02

From all previous posts, the consencus seems to be that the single pots need more fluid than the 4 pots even though they have a smaller area, the longer stroke they require must be the reason. The sliding caliper seems to be pushed slightly at an angle by the 'spring' that holds one half onto the other fixed half's sliding face. If you see what I mean!
Maybe your N/A brakes were borderline and as they wore together that reduced further the fluid required as everything beds in together resulting in a pedal that is OK.

Rich

LOAF

August 4th 2004, 16:25

I have a question,

With all the debate of which M/C to use, can I propose another option..

Not sure if this will work, but food for thought.. I was looking thru the Wilwood Catalogue and noticed they sell may different bore sized tandemn master cylinders.. As well as Proportioning valves.

It may be the more expensive route but at least you could get the front to rear biase correct..

Here are the part numbers that I was looking at..
ADJUSTABLE PROPORTIONING VALVE
PART NUMBER: 260-8419
1” TANDEM MASTER CYLINDER WITH REMOTE RESERVOIRS
PART NUMBER: 260-7563

Haven't gone further with research yet... mounting seems similiar to beetle,
Attachment point to pedal, may require creativity...
They have long strokes to push a good amount of fluid..

All in in would seem like a good option, but not being a brake expert would like to hear some thoughts.. If to much over sized M/C you could use two proportioning valves.. One for the front mounted in the trunk and the other for the rear by the e-brake and play with it till you get it right..
Again just some thoughts.. since I am in the same boat.. except that my parts are still in the basement.. getting there, but not yet..

V/R

ALex
NNJ

zen

August 4th 2004, 16:49

i think Sandeep took a similar path. don't know if he used Wilwood, but similar path.

Pillow

August 5th 2004, 11:01

Why not just use a 911 MC?

Mike Ghia did that on his oval and from what I remember worked out quite well. That is what I would do for a Beetle with all discs.

On my '66 splittie I am running a 944 MC (ATE one - not Girling) with 944 single pots all around. So far the braking has been excellent... But of course a bus is much different than a Beetle weight wise.

Also you can get the "self bleeder" screws if you end up doing the brakes alone a lot. Kind of rich at about $10 each but well worth it if you end up playing with the brakes a lot.

Good Luck,

LOAF

August 5th 2004, 11:31

Pillow,

I read his write up on the 911, but he went with the vacuum assisted Servo and MC I believe.. It seemed like a lot of work for servo assisted brakes..

Not sure if you can run the 911 without the servo.. would be curious..

I just thru out the idea of Wilwood since the are reputable and seemed like a option, that had not been mentioned..

Alex

zen

August 5th 2004, 16:47

i think BoyGenius ended up sticking with the 911 m/s and removed the servo. maybe he will jump in here (assuming he is taking any time off of his new bike). :D

Pillow

August 5th 2004, 23:26

Thanks fot the update Loaf, I did not realize he used the servo on his oval.

But if memory serves me right the early 911s did not have a servo on them, maybe added this feature in 1974...?

Like in my Split the 944 had a servo to begin with but runs just fine without it.

... Just use the 911 MC without the servo, no problem! :)

I have a 1971 Chevy C-10 pickup with manual brakes. If you have enough leg for that then a Beetle is no problem, trust me on that!

LOAF

August 6th 2004, 08:29

Pillow, Zen

Thanks for the update..
I will recheck BG posts to see how much extra work is needed.. If it is minimal, then this seems like a great option.. with what seems like a better break bias..

If this is correct, why isn't everyone using the 911 MC? Seems like a no brainer.. but that's coming from the peanut gallery (me :) )

Alex

boygenius

August 8th 2004, 10:04

I used a 1987 911 sc (if it matters) and I removed the servo. The bolt spacing on the 911 M/C is the same as the beetle at least for the years of 911 that use the same M/C as mine. The M/C is not threaded so I used some longer bolts nuts with lock tite. There is also a flat rubber O-ring on the back side to seal up against the servo but it looks like it will seal up against the frame head nicley. There is one less opening in the M/C for brakes lines so I had to run a "T" fitting in for the front curcuit to retain the brake sensor. Also the angle of the rear exit requires a "LOOP" in the line to avoid kinks so my stock line was too short. If I was going to run a porportioning valve at this time it would fit perfectly right before the rear brake line grommet under the rear seat area since the stock line is too short. I used a Vanangon line since it was something like 8" to 10" longer and I just looped it at the end. The guide tube for the 911 push rod needs to cut down due to the angle at which the beetle rod enters the M/C. The pushrod also needs to be shortened to retain proper pedal geometry but I posted that somewhere before, I'll try to find it... I also ended up replacing most of the stock hard lines with longer ones from my local auto supply store. I'll see if I can put all the information together today if I have time. ( One note though... I haven't actually finished assembling the system so I don't even know how well it will work... )

Jeza

August 10th 2004, 00:50

Boygenius - what size is your 911 master cylinder.

Comments have been made before that the 944 brakes work as a system and although they came off a front engined car using the single pot calipers with the 19mm VW MC makes it even more front biased. From memory the 911 MC has no variation in the front and rear diameters to make up for the ratio of the 944 fronts (huge 54mm) vs the rears (36mm).

Shad Laws made some comments in this thread that are very relevant to this discussion.
http://www.germanlook.com/Forums/showthread.php?t=2183

I'm am slowly getting the 944 MC in so I will let you know what that feels like when its working.

Cheers
Jeremy

Wally

August 10th 2004, 02:50

Jeremy,
That old post of Shad is indeed very informative and gives us the possibility to put some ratio numbers to our 'feel'.

There is one thing that doesn't seem to add up with Shad's calculations though:
Using his front/rear bias ratio calculation, a bigger front cup diameter in your m/c, would yield a more rear biased set-up!?
To stay with the title of this thread: 'that doesn't seem right'

I can't figure this out yet as to why or what I am missing here...?

BTW, I'am running now the N/A 944 rear disks on my square (has stock 42mm front cup caliper diameter), which would give a F/R ratio of 1,36.
It brakes great, but feels just not as powerfull as my former 1303 with the stock 40mm front cup caliper diameter disk and rear 944 N/A, which gave a 1,23 F/R ratio, but that 1.23 ratio may be on the edge in wet conditions.
Because of the square d², a little variation in diameter gives quite a different result in the ratio!

All this leads me to believe that between 1.30 and 1.35 should be about 'right'.

Jeza

August 10th 2004, 06:04

There is one thing that doesn't seem to add up with Shad's calculations though:
Using his front/rear bias ratio calculation, a bigger front cup diameter in your m/c, would yield a more rear biased set-up!?
To stay with the title of this thread: 'that doesn't seem right'

I can't figure this out yet as to why or what I am missing here...?

It a leverage thing, if you increase the diameter of the slave cylinder in relation to the mc you increase the power to the brake. Increasing the MC diameter will increase the hardness of the pedal but not the power to the brake. Jeff Hibbard has a section in his book Baja Bugs and Buggies that explains it well without getting too technical. The most common example is those that increase the size of the slave cylinder in the rear drums / fit T3 drums to increase the braking.

BTW, I'am running now the N/A 944 rear disks on my square (has stock 42mm front cup caliper diameter), which would give a F/R ratio of 1,36.
It brakes great, but feels just not as powerfull as my former 1303 with the stock 40mm front cup caliper diameter disk and rear 944 N/A, which gave a 1,23 F/R ratio, but that 1.23 ratio may be on the edge in wet conditions.
Because of the square d², a little variation in diameter gives quite a different result in the ratio!

All this leads me to believe that between 1.30 and 1.35 should be about 'right'.

What you have now is probably a very good ratio for a rear engined car.

I also ran my beetle with the stock fronts and 944 rears (stock mc) and it brake quite unusually being so rear biased. I imagine you would get away with this most of the time, but my main concern is the differing way they would react when pushed, ie the rears would remain very cool and responsive while the fronts would get very hot and possibly fade (non vented rotor and small pad area in comparison to the rear).

The 944 brakes with the 944 MC gives a ratio of 1.41, which I reckon will probably work quite nicely.

Cheers
Jeremy

PS have you done brake performance comparisons or is it just a feel thing when you mention your 1303's powerful brakes?

Wally

August 10th 2004, 07:38

It a leverage thing, if you increase the diameter of the slave cylinder in relation to the mc you increase the power to the brake.

I agree; it also complies with the formula Shad used.

Increasing the MC diameter will increase the hardness of the pedal but not the power to the brake.

Now that doesn't comply with the leverage formule from Shad!. Tho I think you are very right about the hardness aspect of the pedal thingy.

What you have now is probably a very good ratio for a rear engined car.

Yeah, I agree. Probably safer also in extreme situations than an even lower ratio.

The 944 brakes with the 944 MC gives a ratio of 1.41, which I reckon will probably work quite nicely.

Cheers
Jeremy

Yes, I agree, but the mean reason for the calculated relatively low ratio (for a front engined 944) is that the 23mm (IIRC its 21mm, not 23 mm like in the thread where Shad chimes in, but lets use 23mm for calculations sake) front m/c cup diameter is in the lower part of the equation, thus decreasing the slave/master ratio of the front brakes!!!!!!!
i.e. : 944 fronts:
(54mm caliper cup diameter / 23 mm front m/c cup diameter)²= 5.51
944 rears:
(36mm rear caliper cup / 19.06 mm rear m/c cup diameter)²= 3.57
F/R ratio would then be 1.54
With a 21/19 m/c the ratio would be even higher at (54/21)² / (36/19)² = 1.85.
THATS the point I a trying to make in this equation:
The bigger the front cup of the m/c, the more REAR biased the set-up gets!!!!

Therefore, 180 degrees from my beliefs before, to get a more rear biased set-up from the stock front setten-up 944 brake system, you DO NOT install the stepped m/c the other way around: i.e. 19mm side to the front and the 21/23mm side to the back. That would worsen the problem.
The above holds only true of course IF Shads formula is correct (and 'knewing' Shad, he is quite an educated guy (even then), so I must really believe him)

Jeremy, I am realy curious what your or others thoughts are about my above 'conclusion'. True or false?

This would also explain the enormous front biased'ness' of my current 944 turbo Cup brake set-up on my 1303 SB with the stock 19/19 m/c ! I think I need the biggest step m/c (23/19?) I can find and maybe additionally a bit smaller front calipers or a front propotioning valve (if possible).

PS have you done brake performance comparisons or is it just a feel thing when you mention your 1303's powerful brakes?
No, just a feel thing, but when I drove that car every day back then, I was very aware of any change, even the very subtle ones and this wasn't subtle, but a very, very strong brake action. You can only draw the conclusion that stock bugs are set-up very very conservative with rear break bias.

Greetings,
Walter

Jeza

August 10th 2004, 18:24

The bigger the front cup of the m/c, the more REAR biased the set-up gets!!!!

Therefore, 180 degrees from my beliefs before, to get a more rear biased set-up from the stock front setten-up 944 brake system, you DO NOT install the stepped m/c the other way around: i.e. 19mm side to the front and the 21/23mm side to the back. That would worsen the problem.
The above holds only true of course IF Shads formula is correct (and 'knewing' Shad, he is quite an educated guy (even then), so I must really believe him)

Jeremy, I am realy curious what your or others thoughts are about my above 'conclusion'. True or false?

Walter
You have hit the nail on the head. Now all we need to do is to spread the word, as I think this is where a lot of people get confused and go wrong.

My 944 MC however is definately a 23mm one as it is cast into the body. Actually 23.86 as they are imperial measures which should give me a good front to rear bias (although I don't know where I got the figure above?)

This would also explain the enormous front biased'ness' of my current 944 turbo Cup brake set-up on my 1303 SB with the stock 19/19 m/c ! I think I need the biggest step m/c (23/19?) I can find and maybe additionally a bit smaller front calipers or a front propotioning valve (if possible).

Steve C was chatting to someone on the shoptalkforums a while ago and the comment that came up was that sometimes the science can be taken too far. Sometimes feel / and a few test emergancy stops is the best way to go. To get things perfect you may need one of these
http://www.wilwood.com/products/PedalAssemblies/001-FMP/fmbp/index.asp

No, just a feel thing, but when I drove that car every day back then, I was very aware of any change, even the very subtle ones and this wasn't subtle, but a very, very strong brake action.

It would be good to compare a few test emergancy stops to see how the different setups compare.

Cheers
Jeremy

boygenius

August 10th 2004, 21:37

Boygenius - what size is your 911 master cylinder.

Cheers
Jeremy

To be honest I have no idea. I think I found the specs before I bought it but I can't remember what they are now. There are not any real significant markings on the M/C to denote bore size but the number (20) does appear over the front half of the M/C. Maybe somebody here has access to a porsche 911 service manual and can answer this question.

Wally

August 11th 2004, 01:55

It would be good to compare a few test emergancy stops to see how the different setups compare.

Cheers
Jeremy
Glad you agree. It all makes more sense now! Need to get a 23/19 m/c for the 03 :)

Yeah, I did several emerency stops with my car then, both dry and in the wet and the fronts always (just) locked up first!
A friend of mine with exactly the same set-up (stock VW front disks, 944 n/a rear and stock m/c) but in a 1300 ('68) model and a 2,7 ltr type 4 engine took it to the circuit and reported that on braking hard and steering into a corner, the rear did lock up first.
Now that is a very extreme situation, but shows it really is depending what you do with the car that dictates how you want to set it up!

Thanks Jeremy,
Walter

LOAF

August 11th 2004, 10:27

As I had mentioned earlier, I am leaning on using the Wilwood product line, instead of the 944 MC.

They have a 1-1/16" Tandem Master Cylinder Part # 260-4893

Dimensions and specifications for this master cylinder are as follows:
Piston Diameter 1-1/16 inch, which is equal to 26.98 or 27mm

Fluid Displacement 1.20 Cubic Inches
Stroke Movement 1.35 inch

Bias Split 69% Front, 31% Rear

Given these dimensions, can anyone “guesstimate” if it would be in the ballpark. I would imagine using a proportioning valve for the front. But I am still learning..
Based on earlier readings I would think that the stroke and amount of fluid would be enough to move the 944 N/A single calipers in the front and back.

Thoughts, or comments appreciated?
But based on the front to rear ratio, it would seem like to high 2.2:1.
Alex

Wally

August 11th 2004, 17:06

Need to get a 23/19 m/c for the 03 :)

Just got out and measured the cup sizes of my 944 turbo Cup brakes:
Front: 44,0 mm and 36,0 mm (radial mounted 928S alike)
Back: 30,0 and 28,0 mm

With a 944 n/a 23,81/19,05 (which is even more accurate if the bores are indeed 15/16" and 12/16"), that would give a ratio of 1,23 which is low, but similar to my old 03 which had 1,26 and braked like a boat achor :D
Already saw one on ebay ;)

Greetings,
Walter

Jeza

August 12th 2004, 02:47

As I had mentioned earlier, I am leaning on using the Wilwood product line, instead of the 944 MC.
Good idea.

Based on earlier readings I would think that the stroke and amount of fluid would be enough to move the 944 N/A single calipers in the front and back.
It should be plenty.

Thoughts, or comments appreciated?
But based on the front to rear ratio, it would seem like to high 2.2:1.
Alex

Sorry I can follow Shads calculations and use them on my car but thats where my knowledge stops. As you say the ration front to rear comes out as very front biased, but I don't know how the % bias affects that ratio. I suspect you may be better choosing an option with an adjustable bias bar. This would be a better option than fitting a proportioning valve.

Walter did you do the calculations of your current cup set up (with the 19mm Bug MC) as a comparison?

Cheers
Jeremy

LOAF

August 12th 2004, 09:54

Wally

August 12th 2004, 10:23

Walter did you do the calculations of your current cup set up (with the 19mm Bug MC) as a comparison?

Cheers
Jeremy
Yes, I did: that is now a whopping 1.92 F/R ratio !!
As said before, this does explain my current enormous front bias. I hardly wear off the light rust on the rear disk!

Greets,
Walter

Jeza

August 12th 2004, 17:00

Jeremy..

What is an adjustable Bias Bar..

I assume that this is something built into the MC..

Why is this better than a proportioning valve.. Please explain..

I think I may know why, might have an idea, but in the interest of not sounding to silly please explain..

Thanks
ALex

Alex

I believe that a bias bar allows you to adjust the ratio between the front and rear brakes at the MC. It keeps it even no matter what pressure you put on the pedal. So the percentage split you mentioned before would be adjustable on a bias bar type.

I had a quick look at proportioning valves once. My understanding was that they limit the maximum pressure to those brakes. ie the max pressure plateus at a value so even if you push harder their will be no more pressure applied. They are commonly used in the rear lines to prevent the rears from locking up first- so this makes sense, limit the max pressure available to the rears because at max braking (ie panic stop) there will be a lot of wieght on the front - even in a rear engined car (don't tell me you don't have wieght transfer- how hard are your springs!!! :D ).

But put the proportioning valve in the front line (which is commonly not allowed by authorities) and you limit the max power to the front brakes. I'm sure with an adjustable one it could be set up very well, but I think for the best set up you would be much better off with an adjustable bias bar.

Feel free to comment on anything that I may have explained incorrectly, its a big learning game for me too.

Walter- yes thats quite a difference between the Bug MC and the 944 MC. Ideally you'd get something in the middle that allows a bit of fine tuning to get it just right :cool:

Cheers
Jeremy

boygenius

August 14th 2004, 18:04

I found this regarding the 911 sc master cylinder bore...

http://www.germanlook.com/Forums/showthread.php?t=2908

Jeza

September 19th 2004, 18:34

Hello all

I have been meaning to reply for quite some time to let people watching this thread know how I got on with the 944 MC.

Well it took a bit of fiddling to make it fit which is why its taken so long. I ran 2 new front hardlines, and a short section to a T piece for the rear line. On the T piece I fitted the brake light pressure switch. I'll see how well this works, but have heard that its a bit slow to react. If need be I fit a micro switch to the pedal cluster.

The way I fitted the MC is nothing new, but being a RHD car I did discover that my rear line exits very close to the brace under the spare wheel well. This required a really tight curve to the brake line and also a bit of clearancing to the brace (punch and big hammer). I've also bolted the T piece to a bracket to support it, which I had noticed many people hadn't.

So its mostly bleed up and the pedal feel and travel is 100 times better. I have much less pedal travel than with the Bug master cylinder. The travel is about the same as a Bug MC and stock discs & drums. I have not driven the car yet, but that is hopefully getting closer and I can report back to any that are interested on how it stops and feels then.

Cheers
Jeremy

super vw

September 19th 2004, 22:19

cool, feedback once you drive it would be great!

Later,
Jonathan

LOAF

September 24th 2004, 14:39

Figured I'd chime in again..

Looking for another option to get bias right. As it has been mentioned there may be some advantage to running mulit pot pistons. That being said... I have been researching the Wilwood Line of Calipers. There Forged Dynalite's with 1.75 inch pistons are made for different size rotors. Can't remember size of the N/A 944 but from a quick glance this morning they looked like 1".

I say this because I have been looking for Mulitpiston options that were inexpensive for my WRX, which sees the track. For my particular application, only a bracket needs to be made. Which is where the trial and error as well as some engineering come into play. The mounting method via bracket could be used with the 944 spindles to possible create a nice set up. For the WRX this enables me to use 16in wheels and clear my stock rims.

Thought that this could be another option.. I can machine a bracket but need to find out where to do it.. Getting the dimmensions will be trial and error but for about 125 a caliper, could not hurt.

Any thoughts.. haven't looked at the rear yet, but its probably a bracket away..

Not sure what type of metal to use..
i.e what grade steal or aluminum (sp) any thoughts.. I have heard of alumin. brackets braking..

Jeza

September 24th 2004, 16:57

Can't remember size of the N/A 944 but from a quick glance this morning they looked like 1".

From the info I have (Disc Brakes Australia, DBA) the original thickness is 20mm front and rear.

The mounting method via bracket could be used with the 944 spindles to possible create a nice set up. For the WRX this enables me to use 16in wheels and clear my stock rims.

Thought that this could be another option.. I can machine a bracket but need to find out where to do it.. Getting the dimmensions will be trial and error but for about 125 a caliper, could not hurt.

Any thoughts.. haven't looked at the rear yet, but its probably a bracket away..

Not sure what type of metal to use..
i.e what grade steal or aluminum (sp) any thoughts.. I have heard of alumin. brackets braking..

Check out Steve Cs brakes - he made a bracket to mount 996 rears to the original VW steering knuckle of his 1302.
http://www.clubvw.org.au/porsche_brake_photos.htm

Cheers
Jeremy

hot66

October 5th 2004, 16:01

Jeza

October 5th 2004, 17:22

hot66

I can't say for sure about the VW fittings for the remote reservoir lines as mine didn't fit. My master cylinder is a stock one from a '71 1302. Ricola used the fittings from his Beetle master cylinder in the Porsche master cylinder but did mention that his Beetle mc was an after market one.

I found some fittings that did work successfully on an old BMW (7 series from '70s).

I don't know if VW changed the Beetle mc on later models than mine.

Hope this helps :)

Cheers
Jeremy

super vw

October 21st 2004, 13:40

So, s-beetle or 944 MC?

Jeza

October 21st 2004, 16:16

Jonathan

Sorry I havn't come back with any more info, the car is requiring some rust repair, and I have been waiting to borrow a welder. I say the car will be back on the road soon, but not being the worlds fastest worker it is likely to still be a couple of months.....

However I would go 944 MC (In fact that is what I have done :D ) , and from comments on this thread and others that would be the general consensus for the best MC to match the 944 NA brakes.

Good luck

Cheers
Jeremy

Angelo Amato

November 24th 2004, 18:40

I found a WONDERFUL www for us brake-a-holics !

see my other posting under brakes !

ENJOY ! :)

judgie

November 25th 2004, 13:57

just to let you know ,i used the 944[19/23]master and 944 n/a brakes.
19 to the front and 23 to the back.no dive on brakeing very hard and stops very very well indeed thank you,i think the wheel selection makes a big differance in brake perfomance as well ie;i run 7x16 with 205/55/16 on the front and 8x16 with 225/50/16 on the back so my trye split also helps with the rearwood brake bias.
cheers rob

Che Castro

December 15th 2004, 18:22

I had a look at shad's calculations. how come there is no multiplier for the number of pistons in the caliper?

Jeza

December 15th 2004, 20:04

I had a look at shad's calculations. how come there is no multiplier for the number of pistons in the caliper?

Good question!

I can't say as I know the answer to that, but hopefully some activity on here will lure in a hydralics / fluids engineer to answer
:D

Cheers
Jeremy

Wally

December 16th 2004, 02:50

AKAIK, the two pistons in a 4-pot caliper are never the same diameter, so you must simply add the two of them. Surface is surface after all.

Greetings,
Walter

Jeza

December 16th 2004, 04:15

Wally

I think Che might have been refering to the 2 pistons such as in a standard ghia calliper with 2 40mm pistons.

Some one in our club explained it to me a while back but I completely forget it now. However there was something about just using the area of one piston for some reason.

Cheers
Jeremy

super vw

December 17th 2004, 00:20

Well, i just got my hands on a early 911 (73 targa) MC. i mounted it up, but have not plumbed it yet (still waiting on parts). it bolts right in. i think i is a 19mm?

anyways, i will give this a try to see how the pedal feels once i get it plumed up. If this dosent work out. i will try to find a used 944 MC to try. i want to find the best "bolt on" option, and it seams like a lot of porshe stuff shares the same mounting holes.

Che Castro

December 17th 2004, 06:42

Yep i was referring to the post that was linked on one of the earlier pages.

What I didnt get was why the number of pistons on each caliper wasn't included.

VWader04

December 17th 2004, 23:54

has anyone used or heard about using the
CSP #611 015 000
i heard some where that this would be a good option...but, i don't know though..im in the same boat as everyone else :confused:

20.64mm bore CSP master cylinder (http://www.csp-shop.de/cgi-bin/shop2/shop_main.cgi?func=dlink&wkid=80703235003&artnr=18189a&cat=)

Vdubjim

December 31st 2004, 12:49

accoarding to pelican parts the 911 (up to 89) MC is only 19mm but maybe the volume is more??

and if using the 944 MC which one? there are like 4. EXPENSIVE!!! :(

Master Cylinder For Use With Girling Brake Booster, 944 (1983-86), 924S (1987-88), Each [Photo]
E-355-011-00 $221.55

Master Cylinder For Use With ATE Brake Booster, 944 (1983-86), 924S (1987-88), 944 Turbo (1986), Each
E-355-011-01 $140.20

Master Cylinder For Use With Girling Brake Booster, 944/944S (1987-88), 944S2 (1989-91), Each
E-355-011-10 $258.30

Master Cylinder For Use With ATE Brake Booster, 944/944 Turbo (1987-88), 944S/S2 (1987-91), 968 (1992-95), Each

Also maybe this helps? no pics though. I kow that jettas and stuff have a proportioning valve that basically screws into the MC wonder if this is the same? too bad its NLA.
Brake Pressure Regulator, 944 (1985-91), 944 Turbo (1986-89), Each

Tim

January 1st 2005, 11:15

Hello VWader04,
I am using the CSP 20.64mm m/c but it is used with the Kerscher front brake kit and the reinforced rear cylinders from CSP. I feel better front/rear brake bias and firmer/shorter pedal with the CSP m/c than the stock vw m/c (was used with the Kerscher front kit).

Vdubjim

January 1st 2005, 12:36

i wonder what car that is from?

MattKab

January 1st 2005, 18:14

First of all Happy new year to all!

Shad's formula is standard textbook mechanical advantage formula. As Shad mentioned in his post, we are fortunate, in that we can use the formula in it's stripped down, simplified version. We can ignore factors like friction, radial differences front to rear, pad area, etc. as these can be considered to be constants

Like Wally, I still have the 3/4" T1 m/c and 40/36mm & 30/28mm Brembos (~15,000miles)

I got to a value of 1.72 to the front and I had 1.23 as the bias of NA 944 rears/T1 front and a T1 m/c.

If we had the 1986 only 944T Front calipers with their 36/34mm pots, we would have a bias of 1.45

This compares very well to the stock NA 944 with the Ate calipers bias of 1.44

Now compare this to the very earliest 911 which had a bias of 1.88 for the first year. This was then changed to 1.6

By lengthy mathematic (plus assumptions) I get the T1 front/CB roto hub and stock m/c to have a bias of 1.38

I put Al B's gold custom Bug (with the cool 'flame' wheels and ALL new parts) on our Arex computer test lane and I recorded stock T1discs/drums and m/c to have a bias of 1.57

I have 'invented' an m/c that can be 'made' for our Brembo 4pot systems that will yield a bias of 1.47...

If I fitted the Kerscher split bore m/c my bias would be down to 1.3

m/c bore has no affect on bias, just the leverage ratio.

Feel free to challenge my values, I still have the pages of arithmetic I used. Plus many possible configurations, feel free to ask.

Matt

MattKab

January 1st 2005, 18:24

i wonder what car that is from?

8v Golf ;)

Pillow

January 2nd 2005, 00:16

This might be a good option as well:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33571&item=7943123843&rd=1&ssPageName=WDVW

a 23mm 911 master fitted for the early 911s.

Jeza

January 2nd 2005, 20:28

Thanks for the post Matt

Someone else speaking sense to reinforce the important points.

CU
Jeremy

Wally

January 3rd 2005, 12:39

m/c bore has no affect on bias, just the leverage ratio.

Feel free to challenge my values, I still have the pages of arithmetic I used. Plus many possible configurations, feel free to ask.

Matt
Hi Matt,
I assume your above statement is a 'misprint' ;) ? Anyway, it doesn't seem to match up with Shad's mathematics, who I value greetly.

I just fitted a 944 23/19mm mastercylinder and hope to inform you all the difference on brake bias as opposed to the stock 19/19mm m/c I had before.
Reason for the switch was my terrible brake bias: too little back-side braking.

Oh, I have now fitted the 23mm to the front, as it is stock in the 944, in order to lessen (!) the brake pressure to the front.

Regards,
Walter

MattKab

January 3rd 2005, 14:14

Wally, your talking about changing to a split bore m/c from a m/c with a straight bore. This is how bias is changed ;)

Ok, edit: m/c bore (when F = R, regardless of dia.) has no affect on bias..)

I too have a lot of faith in Shad's calculations and written word, I bet he too would approximate your new bias to be 1.1.. :D

Is there differences in bore sizes between NA 944 and 944T/951? Can anyone confirm? I've asked before..

My idea is to integrate the rear 15/16" piston from a 16v Golf m/c into a 'newly split bored' 13/16' m/c from the 8v Golf. The larger rear piston will push the front calipers and give a front/rear bias of 1.3:1 Similar to the Kerscher m/c :agree:

Wally, my front tyres are only 95% the diameter of my rears, this will have a significant affect on my bias, bringing it close to the 1.6 of a 1980's 911. Which is a little too high for a Bug perhaps. I can't imagine anymore braking power in my Beetle. But I know there is some more there. My eyes already go :eek:

May I suggest you experiment with an adjustable proportioning valve in your rear line. I plan to.

Matt

Vdubjim

January 3rd 2005, 18:23

here is the vw one that looks to be a bolt in.
there is another but the spacing on the mount holes is too far apart
http://germanautoparts.com/Volkswagen/Rabbit/Brake/137/5

these guys are usually the cheapest around and BEST quality. Normal price is 90-110.00 from what ive seen.

Pillow

January 3rd 2005, 19:44

>stock 19/19mm m/c I had before.
Reason for the switch was my terrible brake bias: too little back-side braking.<

Could be because that VW MC is designed for drum brakes instead of the discs.

When I converted the '66 Westi to discs all around Russell at Old Speed said they normally had to rebuild a drum MC to run the discs because there is some "feature" in there that pulls the fluid back to the MC instead of keeping a semi constant pressure residual like a disc MC will. Pardon my lack of technical experience here, just paraphrasing someone elses story :)

I still contend that the 911 19/19 disc/disc MC is the way to go on a Beetle as it is setup very similar in weigh charactaristics and still similar in the disc brake setup (do not quote me on specifics though, but having rebuilt the 911 brake calipers before they are not way different fluid volume wize than 944 units).

Seems to a degree as with anything that certain combos still need tested to determine the perfect conversion MC.

For my IRS build-up (shhh, the pan should be here in two weeks, but do not tell the wife yet) I just bought a 19/19 911 MC to try out with the full 944 single pot setup.... Give me a year or two to post results :(

MattKab

January 4th 2005, 15:52

May I apolagise to Wally, I muddled big-time, you have different (44/36) Brembo's to myself (40/36). I never questioned your math. I see exactly the same ratio's.

Matt :o

Wally

January 4th 2005, 17:17

Haha, no worries Matt ;) I seem to have the rather rare 944 turbo Cup brakes, which have more resemblence to 928 units (i.e. radially mounted up front).
With your addition (F=R), it makes perfectly sense now. You see how easily we can misunderstand each other when we write things down, while thinking ahead already...

Sorry Pillow, but the fact that the bug m/c was designed for rear drums has nothing to do with my bias problems with the huge Brembos I have now.
I will report when the 03 is on the road again with the 23/19 alu 944 m/c.

Regards,
Walter

paul_f

January 4th 2005, 21:23

>stock 19/19mm m/c I had before.

Could be because that VW MC is designed for drum brakes instead of the discs.

When I converted the '66 Westi to discs all around Russell at Old Speed said they normally had to rebuild a drum MC to run the discs because there is some "feature" in there that pulls the fluid back to the MC instead of keeping a semi constant pressure residual like a disc MC will. Pardon my lack of technical experience here, just paraphrasing someone elses story :)

You remembered it the wrong way round!

A drum mc has a residual pressure valve in, of around 10psi, this prevents the springs on the shoes retracting the wheel cylinders all the way in.

On a disc car, if the MC is lower than the calipers, a 2psi residual pressure valve is sold to prevent the brake fluid draining back to the MC and retracting the pads from the discs.

Both of these will cause the first press of the brakes to have excessive travel, if you were to pump the brakes the pedal would rise back up though

Paul

Pillow

January 18th 2005, 17:12

I stand corrected after doing the math. The standard 944 N/A setup seems to be a good bias as compared with the early 911s 1.60 bias.

Just for the record 911 SCs (20.64 master with 48/42 calipers) had a 1.31 bias BUT used a rear preasure regulator that cut in at 33 bar. From "Porsche 911 Performance Handbook" by Bruce Anderson page 216.

... More to come, but I am thinking a 944 MC (23/20) with 911 "A" caliper front (48mm) and 944 rears (36mm) might work well with a 1.34 bias. Very rear heavy for a streeter though I think..?

Thanks,

Jeza

January 18th 2005, 17:22

Adrian

That combo sounds almost perfect :)

I thought the CB kit was very similar in bias

Keep us informed with how you get on.

Cheers
Jeremy

Wally

January 18th 2005, 17:31

... More to come, but I am thinking a 944 MC (23/20) with 911 "A" caliper front (48mm) and 944 rears (36mm) might work well with a 1.34 bias. Very rear heavy for a streeter though I think..?

Thanks,
Be sure to be accurate with your calculation since AFAIK, 23/20 944 MC doesn't exist. In europe all I've come across is 23/19...

Also my 944 rear isn't 36mm, but 38mm IIRC :confused:

Differences in diameter quickly add up in a cross section (surface)! :o

Good luck,
Walter

MattKab

January 18th 2005, 18:27

'23' is more like '24' from 25.4(15/16") = 23.81mm, you knew that..

Matt

Pillow

January 18th 2005, 22:16

Good feedback guys! :)

As for the 944 MC I got this one off a '87 944S model and it is cast into it "23" on one side and "20" on the other. Maybe this is different than the early 944 '83-'86 MCs?

So the 23 is really 23.81, Jess that really does throw the numbers a bit :)

Okay so the 19 or 20 will realy be either 19.05mm (12/16") or 20.64mm (13/16").

I went and measured the single piston 944 calipers (again from a 1987 944S) and I found them to be fairly spot on to the 54mm (53.975) front and 36mm (35.56) rear. Wally I am not sure why yours would be different in Europe?

Thanks,

Wally

January 19th 2005, 02:32

Yes, that is weird.
Weirder is that my early 944 M/C has 23 cast in into the M/C housing for front and 19 cast in for the rear. This would 'suggest' a 'perfect' 23,00 mm and a exact 19,00 mm. :confused:
I haven't taken it apart to verify this tho (and its on the car now)
Maybe there are more different sizes made to suit different countries...who knows?

Best regards,
Walter

Richie

January 19th 2005, 03:26

Hello,

I have lent (sp?) my aluminum 944 Turbo MC to a friend but I hope to get it back one of these days.
Not sure anymore what it said on the outside but as soon as I get it back I'll take it apart and measure the pistons.

Cheers,
Richard

judgie

January 19th 2005, 18:13

my 85 944na m/c is 23mm/19mm.why would the bores be 12/16" when origenaly from germany and would be metric.
the bias realy is a presonal thing , i run 85 na brakes all round and have the 23 to the rear and 19 to the front with 7x16 205/55/16 front and 8x16 225/50/16 back.works spot on for me.
cheers rob

Angelo Amato

January 19th 2005, 18:32

pics

20.65mm dia. bore to run my setup comprising front audi coupe calipers and rear mk4 alloy calipers - cheap e-bay bargain new genuine ATE item ! - not bled them yet - hope it works ! straight bolt on fitment NO mods needed to mast cyl. only rod off brake pedal had to be lengthened 15mm. WHAT A FIT THOUGH ! :laugh:

Angelo Amato

January 19th 2005, 18:33

:cool: amazing 30 years difference !

MattKab

January 19th 2005, 20:11

Yeah, 30 years on and still imperial!

I bet the SAE are to blame for that :rolleyes:

Pillow

January 20th 2005, 11:35

This 23/20 versus 23/19 really pisses me off with 944 N/A brakes!

with a 23/20 (actual 23.81 / 20.64) = 1.69 bias (a little too high I think)

with a 23/19 (actual 23.81 / 19.05) = 1.44 bias (as staded before and a very good bias IMO!)

Arg!

1303R

June 1st 2007, 07:30

i know this is an old thread but i'm trying to work out my brakes. i have n/a 944 fitted along with m/c. i find the brakes a lill front heavy. i work out the ratio to be 1.53. now if i changed the rear calipers to a 40mm piston the ratio would be 1.25. but what is the best set up for a street driven car? would i be better off having more rear brakes and maybe a proportioning limiter?

1303R

June 1st 2007, 07:45

oh hang on. i get 1.44 ratio going off of 23.81 and 19.05 mm m/c sizes. is this deffiatly the right size bore?

Eliasson

June 18th 2007, 17:40

Hi
I rememberd that I read some articles about brakes.
Here is something for all brake-a-holics....

http://www.stoptech.com/tech_info/tech_white_papers.shtml

speedy

July 9th 2007, 12:31

i have read the thread and done the mechanical advantage calculations , but am confussed , i understand the ratio of mc to caliper size but if we have a split bore mc and the front and back pistons move the same amount the 23 will displace more fluid in comparison to the 19 for the same amount of movement , the pressure that can be applied is regulated by the 23 piston because of its bigger size according to the formulea (lower ratio).does this make sense or am i missing something . i aggree the 19 can apply a higher ratio of hydralic pressure but cannot displace as much fluide when on the same shaft as a 23mm piston .Does the 944 front and back pistons work independantly , this is the only possible solution i can think of . Can somebody please clarify the answer or am i going nuts
cheers jon

speedy

July 9th 2007, 23:52

been thinking about this all day and it is sending me nuts , i thought i would give an example and somebody could correct it if i am incorrect .
say if we using wallys calculations (54mm caliper cup diameter / 23 mm front m/c cup diameter)²= 5.51
944 rears:
(36mm rear caliper cup / 19.06 mm rear m/c cup diameter)²= 3.57
F/R ratio would then be 1.54
i understand this this is the ratio of mechanical advantage but and this is the thing i cannot get my head round area is pi r squared so half 23squared *3.1472=419
and half19squared *3.1472=284
so for 1 mm of movement the 23mm piston displaces 419mm of fluide and the 19mm piston 284 mm of fluid if they are on the same shaft then the limiting factor is the amount of force that can be applied to the 23mm piston , as far as ican see increasing the size of the front mc piston will decrease the mechanical ratio but increase the force on the front caliper pistons therefore increasing the bias because the rear cannot displace as much fluid for the same movement please help
jon

1303R

July 10th 2007, 15:12

ahh. i see what you mean. have you tried contacting a brake specialist by email and see what they say? maybe worth trying a few different ones.

super vw

July 11th 2007, 23:23

Well i have been running my early N/A 944 setup (from and rear stock) with the stock M/C (19 front 23 rear) and have to say thay it is front bias (to much really, as i lock up to early due to the very little weight transfer of a 1303 under breaking). i have done 6 Autocross sessions with this set up, and have found adding weight (60 lbs) to the front of the car HELPs A LOT with breaking AND turning (no more scrunbbing in mid turn). anyways im going to swap the front to rear lines Ex: 23mm front and 19mm rear. this should give me more of the rear bias that im looking for. If i get time this week to do it i will post back. Im going to do another Autocross session this weekend.

1303R

July 12th 2007, 14:49

i am right in thinking the 23mm front circuit is the end nearest the driver, 19mm rear is furthest?

speedy

July 12th 2007, 16:53

i belive this is true, in relation to this thread i found this on a 944/924 tech website (sorry 1303r cannot be arsed to type it all ;)

The final note that is relevant here is on brake biasing or proportioning. The front wheels must develop more brake torque (braking power, if you will) than the rears, due to weight transfer under braking, in order to prevent the rear wheels from locking first and spinning the car. This can be achieved many different ways; in modern cars it is now being handled electronically. However, in the 924's, 931's, and 944's, it's handled by hydraulic component sizing (to get the correct ratio front-to-rear). In the 924 and 931, the master cylinder has the same bore size for each circuit, and the front and rear calipers use different sizes to achieve the correct proportioning. The 944 uses a master cylinder with different bore sizes front and rear - since the fronts and rears are on distinct circuits. Therefore, for a given amount of pressure on the brake pedal, a 924/931 will develop identical pressure on all four corners, whereas the 944 will develop more pressure up front than at the rear. It then becomes clear why the brake corner components must be matched with the master cylinder when doing a brake conversion -
The most important thing to remember from this - use the correct brake master cylinder from the car from which the calipers came from when converting, and ensure that the brake lines are plumbed correctly.

this seems to back up my theory on larger overall volume of liquid displaced but lets not forget the weight distribution of a 944 was between 45/55 and later 50/50 ,although not 100 percent certain i think a bugs weight dist will be atleast 40/60 35/65 front to back therefore requiring more rear bias than a 944
any thoughts on this are welcome
cheers jon

1303R

July 13th 2007, 15:51

ok but that still doesn't tell you anything.also where did it come from? grabbing stuff from random forums or the like is not real infomation. i'd like to here from the people who make brake systems. knowing what works for some people doesn't really tell me anything, i'd much rather find out why and how it works. sorry if this sounds off, i'm here to learn, just wanna make sure i'm learning the right info. :)

speedy

July 14th 2007, 14:41

i agree, there is alot of BS**t written on forums that is why when i give an opinion or infomation that i am not 100% sure about i explain where it came from it is then up to the person recieving the info what they do with it anyway the above came fromhttp://www.924.org/techsection/9brakes.htm#2*-%20Brakes%20-%20general%20description when investigating the stepped m/c i have come to realize that there are many factors involved in brake system design it is mind bending , one thing is for sure standard 944 biasing is not the ideal for a beetle as it was calculated for a front engined car(more weight over the front wheels) , on the road under normal conditions this is not an issue but on the track or under heavy use braking distances will be larger than for a car with a well setup bias because the rear brakes will not be working as hard as they could .In theory a bigger set of brakes with bad biasing will increase braking distance over a well biased smaller set of brakes . i think the thing that brought home the importance of the many considerations when designing a system is the fact that on a perfectly balanced braking system(front locks just before back) fitting softer compound tyres on the front alters the biasing because the tyre will then give more grip meaning the rears could lock up first hence the need for a biasing valve to correct this.
anyway enough ramblings
here is a list of some of the considerations when designing an optimal braking system
front to rear weight distribution
spring rate on suspension (effects weight transfer under braking )
ratio of tyre size front to back
weather the car is lowered
downown force of fitted spoilers etc
tyre compound
disk size
area of the pads and compound of the pads used
ratio of calipers and piston size etc
there are others but i cannot remember them
After studying a picture of m/c i now realize that Wally was right ,the Fand R m/c pistons can and must work independantly of each other , after you realize this then it is simple to see how the mechanical advantage formulea will hold true . If you apply 100kg of force to the front piston this will apply 100kg of force to the front caliper and then 100 kg to the rear piston , because the volume of liquid beetween the m/c pistons remains constant the front pistons resting position is dependent on the rear pistons position when it is at 100kg pressure. The system will balance out when both front and back pistons are at 100 kg at this point the mech advantage ratios hold true , sorry it has taken me this long to understand it (must be slow)
Hope this helps
jon

speedy

July 15th 2007, 17:59

OK here is the thing if the above is true and brake pressure ratio is caliper to m/c piston ratio , you have to take into account the fact that the front 23mm piston is pushing a 19mm back piston hydralicaly in the master cylinder .In the calculation this gives a ratio of 1.9 on area guess what the equivelent areas are now 23.8 is 444 and the 19.05 is 443 so if the 23 is nearest the driver it will supply more fluide but not effect the bias at all ie harder pedel on 944 na calipers , maybe this is the reason some people swear 23 on the rear is better and some 23 on the front is better , it seems strange that porsche picked these two bore sizes that when area is calculated as a ratio of each other give the same surface area , could anybody chime in that has infact run the m/c both ways , i would be interested to hear your results and if they match with my calculations .I rang a brake specialist(allegedly) and due to the fact split bores are not that common he could not give me a definative answer , infact no answer :D
cheers jon

Jeza

July 17th 2007, 20:57

Have a read of the 914 tech articles on the Pelican pages, that might help explain a few things.

This one in particular may answer some of your master cylinder questions

http://www.pelicanparts.com/techarticles/914_BMW_calipers/brake_calc2.htm

I have 944 NA brakes front and rear on a 1302 and I find them okay on the street and once warm on the track I really like the way they feel and brake. They may not be perfect, but I suspect they offer better front to rear ratio than most people think. I use the 23.8mm side to the fronts as designed by Porsche. If you read the above tech article you'll see why it is done this way.

Friends with quicker cars than me would like to upgrade their 944 NA's (also on a 1302), but I really think it comes down to what you want and the use you give your car.

Out of curiousity have you compared the front to rear hydrallic ratio of this set up to early 911's, which are more tail heavy than our Beetles are.

Cheers
J

speedy

July 17th 2007, 21:56

Jeza, when i did the calculations i did them converting everything into lbpsi, i read that artical earlier, it is what got me thinking , if you aplly the theory that 100lb from the driver is absolute pressure , this translates into 155psi from the front piston because the piston is less than 1inch squared in area and exerts more pressure because the input pressure is not in psi ,therefore the rear piston because it is less area but pressure is now applied as hydraulic pressure in psi ,it is dependent on the reduction ratioo of the the area,s 444 and 228 which is 1.9 so 79lb of pressure is aplied to the rear circuit ,say we had two pistons on the calipers that were 23mm front and rear the resultant pressure at the front piston would be 23-23 which isa 1-1 ratio so 155lbpsi or 100lb the rear would be 19-23 19mm area=228mm, 23mm area =444mm in area gives a ratio of 1.93 -1 multiply this buy 79 and the answer is 155lb or 100lb absolute it may sound sound confusing but if hydralic pressure is dependant on area then the ratio theory must hold true weather going up or down i put all sorts of caliper piston numbers in and the answers the same, connect the calipers front or back and apart from different pedal pressure it does not matter
what do you think

Sunroof53

July 20th 2007, 09:52

I have been reading this with much interest as i am converting my 66 bug to early 944 na brakes all round. I have done all the mods and machining etc .So to clarify before i do this :1.Swapping the front connections with the rear will make no difference with the 23/19 MC.2.you must use the 23/19 MC if using NA brakes all round.3.No solution for bias issues as it depends on tyres/weight etc.I still have not read any reviews about peoples experiences which i find strange as so many people are doing it .I am looking forward to fitting the brakes but hope all this work will be worth it .

Sunroof53

July 20th 2007, 09:53

:( I have been reading this with much interest as i am converting my 66 bug to early 944 na brakes all round. I have done all the mods and machining etc .So to clarify before i do this :1.Swapping the front connections with the rear will make no difference with the 23/19 MC.2.you must use the 23/19 MC if using NA brakes all round.3.No solution for bias issues as it depends on tyres/weight etc.I still have not read any reviews about peoples experiences which i find strange as so many people are doing it .I am looking forward to fitting the brakes but hope all this work will be worth it .

Eliasson

July 23rd 2007, 14:59

Hello
I m about to fill my brake system with brake fluid and start testing how the braking system is performing.
Whats important for me is two questions.
1. I dont want the M/C to bottom.
2. The rear brakes should never lock before the front ones.

The first ones is quite simple to calculate, if you know how much the pistons retard in the calipers, the amount of oil to puch them back should decide wath to use. And then I use some safty factor. I have 944 T calipers front and rear and I decided to use the original beetle M/C to start with.

The second question is more difficult. Every car on this forum is unique in some way. Ride hight, tire size, spring stiffnes, weight...... So my conclusion is what is right for one car is not right for every car. There could only be guidlines where to start testing.
If you continue the calculationes and find out how much possible braking torque that is produceed at brakedisc. If I have made the calculations right the 944 have a bit more braking torque at the font/rear (55/45%), 911 have around (60/40%) front/rear. That is what the manufacturers decide for thier modells, it could be some kind of guidline to follow?
Then its up to myself to set up the car so the maximum of force could be used for stopping my car. Inceasing or decreasing front and rear bias. Speedy and Super VW have mention some ways to do that in this tread. super vw for example put some weight in the front and then he increased the rear bias.

Anders

speedy

July 23rd 2007, 17:55

putting more weight in the front does increase rear bias by default, this is a good solution to improve beetle braking by shifting a little weight over the front wheels improves grip therefore increasing the braking torque that can be applied ,many people place batterys in the front to accomplish this without adding weight to the car .
A bias valve will only work if the car is rear biased to start with !
Like you said each car is individual , wether you have a spoiler on the front or back, oilcooler up front , tyre size ratio and compound full tank of fuel etc
I think it is down to trial and error to get the balance you are happy with .

super vw

July 24th 2007, 22:44

I already have a Optina Dry cell battery up from (right hand side of car in the corner by the fuel tank and above the spare tire well).
I really should have added a heavy battery (60 lbs or so) to facilitate weight shift better. but then i would have had to give up cargo space.

This week i al going to raise the rear end of the car up about 1/2- 3/4 of an inch to give me some more weight transfer to the front. at the moment i have a perfectly level car with NO rake to speak of, adding a rake will help with the front a bit. I alreay have the front end up on the adjust- a struts max setting (about 1/2 inch fender gap in the front). and i have no fender gap in the rear.
I raised the front to tame down the bump steering issue i had when it was "dumped", much better.... but still the steering tierods are not PERFECTLY level at a settled rest (best for no bump steer).

Although this kind of fine tuning is not going to make the brakes pefect, but it helps to get the car bananced so the brakes can work as well as they can.

The only time i have bias issues is if im not doing controled HARD braking at SPEED (60+) such as autocross events and sudden emergency stops at lower speeds.... and thats related to weight transfer and not having optinum bias). although if i transfer the weight smoothly and with more time i can really bite hard and stop no probelms with very litle tendency to lock up (although it will lock the front still, and thats fine)

So really i should be looking for ways to make the rear brakes work better, thats with hydro, friction changes like pads or mechanical changes such as tires..ect

Ramble....

1303R

July 25th 2007, 12:20

what i'd really like is anti lock brakes. has anyone fitted them on here? can't be that hard can it? i think some later 944's used it

jrinlv

July 25th 2007, 15:59

Sorry I'm too lazy to go look at what you want to do with your car but most "pro" drivers hate anti lock brakes, they say it takes the control away from the driver, but for the street no problem. Just a thought, take care and good luck. JR

1303R

July 25th 2007, 16:02

what "pro driver's"? i wonder why most modern cars have them fitted?

super vw

July 26th 2007, 10:31

All the GT3 Porsche Factory CUP cars have ABS. works fine... better really once you know how to use it. all you do is mash the brakes and you can never lock up ;).

Bug@5speed(US)

July 27th 2007, 10:28

I also have been following this thread, and while my car is still on block, I am very interested.

I have installed the front 944 N/A set up on my car but not run it yet. Intent is to play with the piping and run the 944 MC with a proportioning valve.
I have been pondering a few things. Since this car will run about 75% track (HPDE) and 25% street, my focus is on getting the car set up properly.

From my previous experience playing with different piston calipers, as well as sized, I know first hand the impact this can have on bias as well as feel.

I was thinking of changing to the 4 piston similiar sized (diameter) 944 turbo set up for the purposed of feel. My experience with different track pads on dual piston sliding has been that they tend to be very on/off switch like. With the multi pistons it seemed more progressive and the feel was nicer. Again some of this is a function of the pad (usually carbotech XP series, which have a high initial bite).

So without rambling to much, any thoughts on using a 4 piston front and single piston rear with 944 MC? Which way to pipe, and if prop valve needed.

VR
Alex

1303R

July 27th 2007, 12:21

the trouble with four piston calipers is you need the hubs that go with them from what i've heard, or some sort of conversion caliper mount. the rears are same hole spacing thou, so they easier

speedy

July 27th 2007, 15:03

well with that setup i don't think you will be needing the bias valve:D .
the surface area of the pistons on the front will be quite large compared with the standard giving you a larger front bias ,I run 996 4 piston calipers all round and really like the feel of them , like you said they are not grabby at all plus mine were from a rear engines porsche i would think was more suitably set up for a rear engined car.Im sure mr porsche did all the calculations for me .
To use the bias valve you will have to slightly over bias the back with larger rear pistons on the calipers or improve the grip on the front end to such an extent the rear looses grip first , personally i will be after a balance bar setup when i get round to the next stage in my cars evolution as when sorting the bias it is cheaper altering the bar with a spanner than swapping the calipers etc .
As for the m.c acording to my calculations i does not matter which way round it is just the 23mm piston will supply more fluide but will not alter bias, i use a 19/19 with my setup

Bug@5speed(US)

July 27th 2007, 15:28

With regard to using the 4 pistons, I should have mentioned ditching the old and starting over via one of the many ways: 944 T spindles, or Machined beetle.

I have seen a kit that wilwood makes for the 944 but seems to pricey, maybe I could talk to Lanner to effectivlye do the same for cheaper, Rennlist approx 8-900.

I will leave the rears alone, 944 NA, as they are quite large, and don't think heat dissapation will be an issue. I can probably play around with rear bias thru pad bite, friction coeffecient of the pad. I

I have both type I and the 944 23/19 MC's so I could play around with that also. Not to sure how the bar setup works but I assume this is with independent front and rear MC's

Again, figured I would ask since pedal feel is an attribute that I rank high.
VR
Alex

mabbo

July 2nd 2008, 14:26

bug@5speed:
did you ever get the 4 piston 944 turbo calipers fitted to the front along with the 944 single slider rears? this is one of the options i have been considering..
mabbo

Wally

July 2nd 2008, 16:23

I have had the 23/19 944 MC on the car for a year or two now and have just changed it out to an original bug 19/19mm MC.
Will let you all know how it works out ;)

Simon

July 2nd 2008, 19:10

bug@5speed:
did you ever get the 4 piston 944 turbo calipers fitted to the front along with the 944 single slider rears? this is one of the options i have been considering..
mabbo
I'd get something bigger for the rears (or something smaller for the front), because the rears can handle more braking than you'd expect (Weight distribution stationary is about 40:60 front:rear, and it doesn't change as much when braking since we have a rear-engined car :))

jmd

December 2nd 2008, 17:26

wally,
Why if its running, make the change to the other MC?

I am setting up a 4pot porsche caliper (944T) front/rear (bigger front pistons) and have the 944T MC but not installed (its a bare pan at the moment). I have followed all these posts and their multi-directional advice and am still a smidge confused.

Is there anyone running a finished car that uses 69' -ish IRS chassis with a full front/rear 944T brake conversion that is up and running smoothly for a little while that can comment on how it works??

If so, did you replace all the hard brake lines?
Also, did you use the original VW hard lines or did you convert the hard lines from the MC to the Calipers to use 944 stuff?

Is there anyone actually running an MC that is setup with a balance bar / proportioning valve? If so what parts and are there images of this configuration.

As useful as our forum is there is data allllll over the damn place... and all of it is in total bits and pieces with loads of speculation and opinion instead of historic and documented fact... is there one single post for a few things such as "944 Brake Conversions - all you need to know from calipers to MC's" or "944 Suspension conversions - all you need to know from alu arms to steelies to skinny or fat stances (not so important as the brakes)"... this type of 'organized' information would be awesome to reference...

and as much as asking a question around here gets the standard response "Its in the forum look it up"... well, thats all well and good but the community is to support its fellows by organizing and quantifying that data into useful and organized chunks, hopefully validated with user experience and images to support the learning curve...

Is there anything I can personally do to support this effort?

jmd

December 2nd 2008, 17:37

Wally

December 2nd 2008, 17:59

wally,
Why if its running, make the change to the other MC?

I still had too much front bias, Weird, but true for me.
The 944 23/19 MC gave a VERY high and super hard pedal, but too little braking force imo.
The 19/19 stock MC gave a little less pedal effort and a normal high and hard pedal. Not the dramatic change I'd hoped for, but its a bit better now.

Sorry that this is probably again confusing wrt others experience :o
Maybe you can conclude s/th from that (seriously though) :rolleyes:

jmd

December 3rd 2008, 00:06

Wally

December 3rd 2008, 04:27

I can dig that.
So given that I drive a VR6 Corrado (to be honest, thrash its wheels off) as a DD I have a specific expectation of my brakes. to that end I wonder if your a spirited / late braking driver that loves getting deep into an apex with a little trail brake? Do you ever drive with left foot braking? Also can you confirm your brake setup by listing its parts from MC to Calipers including Pads and caliper side-lines?

What brake lines are you running from MC to Caliper Line?

As well, by "VERY High" pedal do you mean that it takes just a tiny input for a grand output? and can you define the base of "Tiny" meaning, 1/8" throw / 1/4" throw / 1" throw?

thanks for any insights...
Toooo many qqquestions :lmao:

I could list everything (most I have already in other threads tho), but i think it won't help you or others. My conclusion is that everybody's set-up is so different, that no generic conclusions can be drawn from one persons car.
I only know that just 944 n/a rear disks with stock disk set-up on the front (us 'ghia' disks), everything else stock, works awesome and is still the best balanced i've encountered.

But if you must know: front 330x28 with GT2 (yellow) rear calipers with stock front 964 pads. Rear 300x24 with 993 rear calipers, stock pads. Rear cups in the 993 calipers are bigger (!) than the (rear)GT2 ones I have on the front axle, but still lock up on the front first! My weight balance is also very towards the front for a beetle. Its about 44-56%.
I have a Tilton bias regulator but its all up to give max pressure to the rear, though I suspect it already gives a reduction to the rear even if its lever is in the max flow position :confused:

By very high pedal I mean like just 1/64 throw or s/th. But I have braided stainless all around.

Unfortunately I don't do left foot braking and can't do heel-toe with my stock pedal-set.

Hope this helps you (but I doubt it as I don't understand either yet...)

Regards,
Walter

Simon

December 9th 2008, 16:10

I have a Tilton bias regulator but its all up to give max pressure to the rear, though I suspect it already gives a reduction to the rear even if its lever is in the max flow position :confused:
FYI:
On its max setting it does reduce the pressure, but only above 69 bars.
Every 1 bar over 69bars input pressure results in 0,5 extra output pressure.

See: http://www.tiltonracing.com/pdfs/98-1261_Prop_valves.pdf

Wally

December 9th 2008, 17:43

Yeah, your right Simon. Took me a while to figure out the 69 bar came from 1000 psi divided by 14.7 :o
Now you mention it, it might be nice to have a notion of what brake pressures arise when we brake in our little cars. That way, you could also get a feel of where to approxemately set the bias lever. Maybe I have it a a point where the brake line pressure never comes...?

Your a Saint ;)

Simon

December 9th 2008, 18:51

I don't know the exact ratio of the stock pedal, still have to measure it actually :o

When the pedal ratio is know as well as the force used to push on the pedal (somewhere between 25 and 60 kgs usually) the line pressure can be calculated.

evilC

December 10th 2008, 06:18

5.1:1 last time I checked

proudbugowner

September 24th 2015, 19:40

Sorry to bring this thread back to life, but I researched and unfortunately a stepped bore master cylinder does not affect brake bias. :-( I hope I am wrong, but I think I'm not. They call those master cylinders (quick take up) and they are made to work together with low drag calipers..

Have a look here (http://www.germanlook.net/forums/showpost.php?p=89802&postcount=12).

Wally

September 27th 2015, 03:26

Sorry to bring this thread back to life, but I researched and unfortunately a stepped bore master cylinder does not affect brake bias. :-(

WTIW, I think you're right. I 'feel' (pun intended) the size of the bore of the master cylinder is mainly meant to match the total size of the caliper pistons, so pedal travel remains acceptable.

flat

October 7th 2015, 02:18

Thats correct. The primary piston (23mm) fluid actuates the rear piston 19mm. They are not mechanically linked unless in event of one circuit failure, so equal pressure in both front and rear master cylinder pistons. The step is for volume not pressure.

I've built many bugs with 944na, 944t, 986, 986S/996 with stock beetle 19mm dual circuit mc with great results. Pedal feel is really good, except the 944na where it is slightly low... if that is unacceptable to customer then I put in the 944mc.

With split busses I typicaly build them (944na, 986, 996 etc) with early modified single circuit mc. Yup single circuit, works awesome. Due to pedal ratio the 944NA brake system on single mc works well without as low a pedal as beetle. Again for higher pedal I can use 944mc as option but typical isnt an exercised option by my customers. (Single bus is 22mm mc).

H2OSB

February 25th 2018, 14:42

I think this thread will be revisited frequently over the years...like I'm doing now, because we all go through what this thread is trying to address. I talk to Flat all the time, trying to figure this all out. Basically, I've decided to run n/a 944 with their single 35.9mm pistons on the rear, and some variation of 42mm 2 pot calipers on the front. I chose this based upon word from two guys who's empirical data I totally respect (not that I don't respect others, but these two guys, we can mostly all agree have a lot of experience to base their opinions upon), Steve Carter, and Walter. Both of these guys whether recently or in the past have told me they had VERY balanced brake set ups with the above mentioned sizes. In Walter's case, he used 40mm stock Ghia type front brakes, and with Steve, he said it was late T3 front brakes (which are the same as early Porsche 914/VW T4). That's enough for me. Well, in reality, I was ok with what Steve told me a couple of years ago, and Walter recently confirmed it.

The rear is very easy on an IRS Beetle. I just bought the tubes and swans Lanner (aka Flat) sells and the set up is an easy and direct bolt on with factory VW parking brake cables.

The front is not quite as straight forward, but ultimately not super difficult. Right now, I've got the 944 front spindles on my car, due mainly to the fact I bought the damn Kerscher ball joints and would hate to throw that much money away. So I'm trying to work out how to attach early 914 front calipers to the 944 spindles. The bolt spacing for the caliper(s) is the same as the 944, however, when the caliper is set on the 944 rotor, the holes are about 1/2 a hole too far away to bolt up. Oddly enough, the offset is very close to right on. If you're wondering how I'm make calipers meant for solid rotors fit over 20mm wide vented rotors, I will tell you (per info gleened from Eric Shea of PMB Performance), the 10mm spacers and all hardware from a 70-83 Porsche 911 REAR M calipers can by used to make the calipers fit (width-wise). The rear M calipers is the exact same casting as the EARLY 914 front caliper (thus also use the same pads), with spacers added.

Perhaps a FAR easier way to approach this...and one I may fall back on, CSP from Germany sells a kit that has 20mm wide vented front rotohubs in the 5x130 PCD I need. These rotors go directly onto the stock 1303 spindle and the calipers have the same bolt spacing as your typical Ghia caliper (not sure the exact measurement, but it's less than the 3 inch bolt spacing of the Porsche 944 spindle). These calipers are made to bolt to any of the many Super Beetle caliper adapters needed for those of us who don't have Super Beetle disc brake spindles (pretty much everyone in the States) and give the correct offset over the rotors. The advantage of this: It's a bolt on solution and I'd be done with it. The disadvantage: The rotors are specialized (though I BELIEVE made by Sebro) and I have no idea the source of the calipers, in the event either has to be replaced in the future, who knows if CSP will still exist and thus the parts available. In reality, CSP has been around for many many years and will likely be around for many many more. That said, I REALLY like the idea I could walk into most any auto parts store in the States and buy either calipers or rotors if need be, should I choose to use the Porsche parts. I'm going to give the Porsche parts the good college try. Honestly, all I need is an adapter to mount the calipers and I'll be good to go. I'm going to try making a pattern from plexiglas.

H2OSB

Wally

February 25th 2018, 15:10

Hi John,

Very true indeed: stock front disks and 944 n/a rears on stock MC is what gave me rock hard pedal and awesome brake balance!
In fact, liked that so much that for my 'daily driver' project, I got a set of fresh stock sized disks in 5x130 from CB, because I liked the alu hub a lot. By now I have acuired parts for a rear 944 20mm disk set up (vented/drileld of course :D) as we, so I'am close to the swap :-)

http://www.keversite.nl/fotoalbum/fotos/144773.jpg

Here you can just see (through the rim) the also new, drilled, 944 n/a rotor bolted to the rear IRS hub:
https://farm5.staticflickr.com/4518/38493566572_127e8c0a37_b.jpg

H2OSB

February 25th 2018, 15:17

Wally--

Do you have any old n/a 944 rotors handy? I've often wondered how close those hubs are to working with 20mm wide 944 rotors

john

H2OSB

February 25th 2018, 15:27

Here you can just see (through the rim) the also new, drilled, 944 n/a rotor bolted to the rear IRS hub:
https://farm5.staticflickr.com/4518/38493566572_127e8c0a37_b.jpg

These wheels make me break into a cold sweat. I want a set something fierce for autocross tires

Wally

February 25th 2018, 15:48

You will even more if I tell you what they weigh :cool: (just 5,3 kg, similar to the magnesium gas burners iirc)

Wally

February 25th 2018, 15:50

Wally--

Do you have any old n/a 944 rotors handy? I've often wondered how close those hubs are to working with 20mm wide 944 rotors

john
You mean trying to put a rear 944 n/a rotor onto one of these alu front type 1 hubs?

H2OSB

February 25th 2018, 15:50

Don't think I don't know that. Flat has a set of the even LIGHTER ones he teases me with pictures of from time to time. Someday.....

H2OSB

February 25th 2018, 15:51

You mean trying to put a rear 944 n/a rotor onto one of these alu front type 1 hubs?

No, the front. It attaches the same way as the CB rotor. I've also considered getting a set of those hubs/rotors, removing the rotor and turning the hub slightly to fit inside a late 944 rotors (the ones that fit OVER the hub).

Wally

February 25th 2018, 15:56

No, the front. It attaches the same way as the CB rotor

Ah! Now I see why you said used n/a rotor :rolleyes:
But euh...no, sorry. Due to me trying to minimize parts hoarding a bit, I brought all old rusty rotors to the dump.. sorry.

Wally

February 25th 2018, 16:00

Don't think I don't know that. Flat has a set of the even LIGHTER ones he teases me with pictures of from time to time. Someday.....

Oh, do tell! Are they also 5,5 x 15" ?

H2OSB

February 25th 2018, 16:00

Ah! Now I see why you said used n/a rotor :rolleyes:
But euh...no, sorry. Due to me trying to minimize parts hoarding a bit, I brought all old rusty rotors to the dump.. sorry.

It's all good. Can you please measure the bolt circle of the rotor attachment bolts? The 944 has a 126mm bolt circle.

I actually kinda got on the guy at CB who designed those hubs/rotors. I asked "why would you re-invent the wheel, so to speak, when Porsche rotors are readily available?" He had no answer.

H2OSB

February 25th 2018, 16:04

Oh, do tell! Are they also 5,5 x 15" ?

They're about 10lbs per wheel (not sure what that is in Kg). Incredibly light. Yes, 15x5.5 with the same offset as your wheels. Only, they're made of unobtainium and incredibly expensive. If you happen upon a set for a good price (well, more likely, individual wheels), they're worth it, but unless you have a Porsche owner income, you'd be well ahead to just get custom race wheels made. https://rennlist.com/forums/924-931-944-951-968-forum/389553-wtb-still-need-1-more-944-space-saver-spare.html First wheel you see in this thread. Holy crap, if you read through the thread with the wheel pic, one guy sold a wheel to the original poster for $10 plus shipping. He could turn around and resell that wheel for $500 in the right place.

Wally

February 25th 2018, 16:06

I asked "why would you re-invent the wheel, so to speak, when Porsche rotors are readily available?" He had no answer.

Interesting!
I think all porsche rotors (except the 914 rears) are vented and they wanted something for the type 1 market?

I'll try to measure the bolt spacing ;-)

H2OSB

February 25th 2018, 16:09

Interesting!
I think all porsche rotors (except the 914 rears) are vented and they wanted something for the type 1 market?

I'll try to measure the bolt spacing ;-)

Their source for un-drilled rotors has dried up so they needed something to offer a 5x130 pcd for the front. A lot of potential...which I don't think they realized (well, perhaps not until I started bugging them about it)

Wally

February 25th 2018, 16:21

Their source for un-drilled rotors has dried up so they needed something to offer a 5x130 pcd for the front. A lot of potential...which I don't think they realized (well, perhaps not until I started bugging them about it)

Interesting indeed.
I just measured it, but was difficult to do. I needed to sort-of eye-ball it a bit, but I think its about 112-113mm bolt spacing. What is the 944 n/a ?

They are big bolts however, like M10, not the M6 of the original 944 n/a front hubs.. (on which 911 3,2 rotors in 24mm thickness also fit BTW, but you may already know that).

H2OSB

February 25th 2018, 16:26

Interesting indeed.
I just measured it, but was difficult to do. I needed to sort-of eye-ball it a bit, but I think its about 112-113mm bolt spacing. What is the 944 n/a ?

They are big bolts however, like M10, not the M6 of the original 944 n/a front hubs.. (on which 911 3,2 rotors in 24mm thickness also fit BTW, but you may already know that).

I suspected it wasn't the same :( They didn't even consider the Porsche rotor when they created those. The n/a 944 bolt circle is 126mm. I did know the later rotors would fit. Flat told me that some time back (in the event I could use those 44mm 964 C2 rear calipers on the front). I wonder if n/a 944 rotors could be re-drilled in the off spaces to fit the CB hubs? 944 rotors are dirt cheap (I bought my set for $13 per side). I MAY try experimenting to see if it would work.

Edit: NVM, I just went out and looked at my 944 rotors. There's not enough meat to the inside of the 126mm bolt circle to drill M10 holes, much less on a tighter bolt circle. If the CB hubs don't have enough meat outside their bolt circle for a M6 holes, it's a non-starter

Wally

February 25th 2018, 16:35

H2OSB

February 25th 2018, 16:38

Is it that difficult to find 944 n/a hubs then? I thought they just needed two (or even just one?) adapter sleeves for the bearings to fit the beetle spindles? 944 is alu too and the CB hubs can't be bought separate iirc?

Nah, that's doable. They are getting a bit more difficult to find, but I think I have 3 sets. The difficult part is finding someone to do the machine work. Flat does that work, but he's only at it part time and has a huge que of people who want his work. Most of my local machine shops try to send me elsewhere. They don't like one-off projects and cannot comprehend why I'd put custom brakes on a Beetle.

H2OSB

February 25th 2018, 16:42

Is it that difficult to find 944 n/a hubs then? I thought they just needed two (or even just one?) adapter sleeves for the bearings to fit the beetle spindles? 944 is alu too and the CB hubs can't be bought separate iirc?

CB hubs cannot be bought separate, but the hub/rotor is not expensive compared to, say, custom made hubs. You can buy the rotors separate. They're about $50 per side, versus the hub/rotor together for about $159 per side. Buy the set, remove the rotor and resell for $45. Cheap hubs, made for the VW spindle and in a 5x130 pcd.

Wally

February 25th 2018, 16:43

They're about 10lbs per wheel (not sure what that is in Kg). Incredibly light. Yes, 15x5.5 with the same offset as your wheels. Only, they're made of unobtainium and incredibly expensive. If you happen upon a set for a good price (well, more likely, individual wheels), they're worth it, but unless you have a Porsche owner income, you'd be well ahead to just get custom race wheels made. https://rennlist.com/forums/924-931-944-951-968-forum/389553-wtb-still-need-1-more-944-space-saver-spare.html First wheel you see in this thread. Holy crap, if you read through the thread with the wheel pic, one guy sold a wheel to the original poster for $10 plus shipping. He could turn around and resell that wheel for $500 in the right place.

Ah, yeah, I saw a 356 outlaw or some custom coach one with these back then. That is also where I got the idea to use these. I had one set welded +1,5" for the rear only for drag racing a few years ago and they holded up fine. Welded very easy, so very good quality alu I was told :-)
I had one in 16", but without the outer holes, but still rare I think. Edit: I see this was the hot one...and I sold it for what I got it indeed an outlaw builder for 250 euro's...
Mine are older 928 spares ;-)

BTW the 356 ones are 11 lbs. Pretty close to my 5,3 kg (11 lbs or so) I think, but yeah, very rare!

Wally

February 25th 2018, 17:37

I If the CB hubs don't have enough meat outside their bolt circle for a M6 holes, it's a non-starter

Hmm, there is plenty 'meat' to drill a wider pattern I think. Seems pretty solid, but the disk is still on it. I'll look sometime coming days to get you more info ;)

H2OSB

February 25th 2018, 18:00

effvee

February 27th 2018, 19:28

https://farm5.staticflickr.com/4518/38493566572_127e8c0a37_b.jpg[/QUOTE]

Man, I really like those rims. What car did they come from? Are they 15 inch?

Wally

March 3rd 2018, 04:37

The trouble with drilling into the hub in the offspaces is that's where the studs are. Is there enough room inline with the current holes to drill an M6 hole? Perhaps offset betwixt the M10 holes and the studs?

To answer that, I took a few pix for you. In short: yes, I think there is enough meat and room for additional M6 studs ;)
In fact, the CB whole hub is dimentionally very close to the early 944 hub.

https://farm5.staticflickr.com/4721/40587997001_5cf8b757c9_b.jpg

https://farm5.staticflickr.com/4612/40587994291_af2748acac_b.jpg

https://farm5.staticflickr.com/4612/39693272175_f9741fc7a5_b.jpg

@Francelle: the answers to your question are already given in the posts above ;-)

effvee

March 3rd 2018, 05:26

Ok, I will read again.

H2OSB

March 3rd 2018, 09:42

To answer that, I took a few pix for you. In short: yes, I think there is enough meat and room for additional M6 studs ;)
In fact, the CB whole hub is dimentionally very close to the early 944 hub.

https://farm5.staticflickr.com/4721/40587997001_5cf8b757c9_b.jpg

https://farm5.staticflickr.com/4612/40587994291_af2748acac_b.jpg

https://farm5.staticflickr.com/4612/39693272175_f9741fc7a5_b.jpg

@Francelle: the answers to your question are already given in the posts above ;-)

Thanks Wally for the great pics. That hub has a lot of potential. That said, it's looking real good with my 914 caliper on 944 rotor set up. Write up soon to follow. Turned out to be FAR easier than expected...particularly with how little I've spent.

H2OSB

May 31st 2018, 23:22

Little update. So the brakes I'm doing for the front of my 1303 are the following: I'm using Porsche 944 spindles with a "flip-it kit" to relocate the direction of the tie rod ends. Due to this, I'm also using Kerscher ball joints. For the actual brakes, I'm using 944 rotors that have had the DIAMETER reduced by 1 inch (25mm). This allows a typical Porsche 914 caliper to bolt onto the 944 spindle and have enough swing clearance for the rotor to fit inside. The rotors diameter PERFECTLY places the 914 (D30) pad on the rotor. Now, obviously, 914 calipers are made for 11mm wide solid rotors and the 944 vented rotor is 20mm wide. This is corrected by salvaging the spacers from a set of Porsche REAR M calipers.

The Porsche rear M calipers is the SAME casting as the 914 EARLY front calipers, so if you can find a set of the rear calipers in good condition, all of the hardware can be used (bolts, spacers, pad hangers). This is important because both the 914 caliper and the rear M caliper use non-standardized M7 bolts, the M calipers bolts being the infamous Ribe bolts (pronounced ree-bee) which have been out of production for about 40 years, and cost roughly their weight in gold, assuming you can find them. That said, the longer bolts are required to compensate for the width of the spacer, however, one could use the longer of the two original 914 caliper bolts as the shorter bolt once the spacers are in place, and just get longer bolts for the other spot. In my case, the rear M calipers I purchased had three of the Ribe bolts ruined due to some previous owner attempting to use the wrong tool to remove them. A Torx head of the correct size can be used to remove them, however, torquing them, it's suggested by "those who know" to use the correct Ribe bit.

Both Lanner Khan (aka Flat) and my machinist friend (who turned down the rotors) thought me silly for what *I* did, which was purchase the correct length M7 socket head bolts from a company called Tola-tool in Germany(Tola-tool was the ONLY company I could find who offered both the correct length AND hardness (12.9) for brake caliper use.). Both suggested re-drilling the holes in the calipers to M8 (a standardized size that is FAR easier to obtain) in the case of Lanner or 5/16th inch (also standardized) in the case of my machinist friend. The reason this was silly was the fact the shipping from Germany to California was almost exactly TWICE the cost of the bolts themselves...which weren't cheap. I elected to not re-drill the calipers out of fear there simply wasn't enough material in the calipers to do this. In the end, I'm happy with the bolts. Cry once, as they say.

So, the results of my mods made for a very slick setup that seemed almost meant to be. The caliper is centered over the rotor perfectly with the use of a 2mm shim placed between the caliper mounting ears and the spindle. However, as I was fitting everything together I discovered my first (and really only) major hurdle. The outside of the caliper body hits the HUB edge when everything is bolted on place. I had been fitting everything up with a pair of junk split 914 calipers with the pistons removed to make trial fitting easier. I tried to clearance the calipers a bit but discovered there simply isn't enough material on the body where the piston lives to take material away. Fortunately, I know Flat. Lanner has had a set of 944 hubs on his bus for years that he has turned down by 8mm in overall diameter. I know from my caliper clearancing effort, I only need to remove approximately 2.5mm for the caliper to clear the hub, so 4mm is more than enough for good clearance, thus I'm sending them up to Lanner to have him turn them for me.

Wally

June 1st 2018, 12:36

Thats some dedication!

A picture of the finished set-up would be cool :)

effvee

June 2nd 2018, 02:04

Yeah, eye candy:)

H2OSB

June 3rd 2018, 03:29

Thats some dedication!

A picture of the finished set-up would be cool :)

Quite honestly, I've thought of going with something easier to put together several times, but I've spent too much on those damn calipers (the German bolts AND the sacrificial Porsche rear M calipers) to abandon them.

Sadly, I sent out on this path simply because I wanted vented rotors on the front, to match my vented rotors on the rear (straight 944 rear brakes).

CSP offers a kit that give 20mm wide rotors with a 42mm piston caliper. These bolt to any typical caliper adapter made for a 1303 without disc brakes (or the ever rare disc brake spindles), thus they have 2.25 inch bolt spacing. Unfortunately there is no way for me to get these for less than a LOT of money. CIP1 is the importer for CSP products in the States. They will special order the kit for me for $1300. Now, that's for JUST two rotors and two calipers, not including shipping. WAY more than I'd like to spend. The other alternative for me, if I must have vented rotors, is having someone like Flat make a set of caliper adapters that bolt to 1303 spindles and having the 944 hubs modded to fit the 1303 spindle.

That all said, I think the turning down of the 944 hubs will yield the results I seek.

Pictures of the finished brakes, will, of course, follow.

Tzepesh

August 27th 2018, 09:55

I have 944NA brakes now on 1303S, with stock 19.05mm master cylinder. I have a set of 944T 4 pot brakes that I will swap on my car, so I've been reading a lot on brakes lately. This thread was a wealth of information. So I tried to plug in some data in the "formulas" used before:
1. 944NA brakes (54mm and 36mm slave cylinders) with 19.05mm pump.
(54/19.05)sq=8.0352.
(36/19.05)sq=3.5712
Resulting ratio is 2.25. So huge front bias. Same result if using 23.8mm pump or stepped 23.8/19.05mm pump (explanation why stepped pump is not affecting bias is here: https://www.germanlook.net/forums/showthread.php?t=2183). The stepped pump just increases the volume of brake fluid going to the front slave cylinders and makes the pedal harder. This explains what I saw during "MOT", a high efficiency of front brakes (80%) compared to rear (40-50%), this being correlated to front and rear weight. So I do not see any other option except bias bars (or dual pumps) to overcome this issue.
Pedal feel is great from my point of view, soft and long travel. I hate hard and short pedal.
2. Considering 944T brakes (40/36 front and 30/28 rear) with 19.05mm pump (same would be with any other pump):
((40+36)/19.05)sq=15.9161
((30+28)/19.05)sq=9.2697
Ratio is 1.717, so still front biased, but much less. Now, considering the same piston sizes were used in 930 with a 23.8mm pump (no step), and that the 930 is has a closer static/dynamic weight ratio to Bug (both rear engined), compared to 944 (front engined), it seems these brakes will be much better suited for a Bug, ratio-wise not power-wise. I'll try with the stock 19.05 pump first, I have read a lot of positive feedback on this setup.

But a question that still remains is why did 944T have a stepped pump with the 4 pot brakes and 930 straight pump, if the step in the pump actually does not affect bias. Just for volume?

Did I understand this correctly? Some older calculations took into consideration for the ratio the master cylinder different steps, but that seems to be false according hydrodynamic laws. That would hold true if the two pistons in the master cylinder would be hard connected to each other, which they are not.

Wally

August 27th 2018, 10:56

IJust for volume?

Yep.
Thats my experience anyways.

Tzepesh

August 27th 2018, 13:43

Thanks Wally for the confirmation. So it seems that 944T brakes would actually fit better the Bug than the 944NA.
I have a curiosity: how do you know which brakes lock up first, front or rear? Do you just feel the car in a specific way? I locked my brakes up a couple of times on hard braking in traffic, but I can not tell which ones did. I just heard the wheels squeak, no deviation from straight line. Can you feel that in specific conditions, on track, for example during hard brake on cornering? I only use my car in normal traffic, which also means some mountain roads, so I did not race it nor do I intend to do so. My "feeling" of the car is that of a normal driver, I have no idea how it is on a track (hm, it was only once at a VW meeting where we had a small autoX track, but that was long time ago and I had no mods).

Wally

August 28th 2018, 02:43

Oh, I really do feel if front or rear locks up first, very clearly. It happens sometimes on an emergency brake situation or if you simulate one.
You really should feel it!
My advise would be to wait for rain and then just stand on it in different situations and in those street situations/surfaces in the wet, it should still never lock up rears first from a safety standpoint.
Just please be carefull when you try this. Be very sure you have room on the road to slip/skid a little and no other cars behind or in front of you ;-)

eskamobob1

October 5th 2018, 20:05

Anyone mind going over the math for why a stepped MC does not effect the preasure output by each cylinder?

A dual MC is set up with a floating piston between the two separate cylinders.

https://i.imgur.com/8L2UI7y.jpg

if we assume we are at steady state (piston no longer moving, just generating more or less force), that the brake line ports are plugged, and that this piston is not connected by a bar and the spring force is minimal when breaking, the pressure in the primary circuit (P1) is going to be the input force (Fin) divided by the plunger area (A1). Without any solid connection or added force between the two channels, Fin must be equal to the force the fluid in the first circuit applies to the floating piston (F1) must be equal to Fin. Secondly, the force the floating piston applies to the second circuit (F2) must be equal to the force applied by the fluid in the primary circuit. This force (F2) is equal to the pressure (P2) in the piston multiplied by the area applying the pressure (A2). Therefor, if the area of the two circuits are not identical, the pressure within them will be different as well

https://i.imgur.com/zyKaxyp.jpg

Tzepesh

November 27th 2018, 05:05

I'll just leave this here not to confuse people.
eskamobob1, I agree partly to your argumentation. But what you have drawn is exactly what it is NOT in the stepped pump (the pistons of different areas are NOT hard linked together). The forces and pressures you computed are correct however if the secondary piston would look like that. But the inside of the pump looks like in the picture from the link https://www.germanlook.net/forums/showthread.php?t=2183. Meaning that the force applied to the second piston is NOT the input pedal force, but it is derived from the pressure of the first: pressure in first chamber (P1) is Fin/d1 (say 400N and 23mm as in the picture), and the force on the second piston is P1*D2 (19mm for second piston). Thus the pressure in the second circuit is the same as in the first circuit.
Your idea would work if the pump would look like below inside, but as far as I know, it does not...