Yeah, 30 years on and still imperial!

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

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!

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?

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?

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

http://www.stoptech.com/tech_info/te...e_papers.shtml

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

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

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.

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.

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

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

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. :)

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/9brak...%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

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

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/techarti...rake_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

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

Just to clarify?
 

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 .

Just to clarify?
 

:( 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 .

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

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 .

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....

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

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

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

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 ;).

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

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

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

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

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 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 ;)

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 :))

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?

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?

Edited: (this is designed to be more motivational and supportive, far more than its supposed to be a rant / bitch session...)

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:

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

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-...rop_valves.pdf

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 ;)

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.