Why 944 Mcyl vs 911?

[DORIGTT]

Why does everyone seem to use the 944 mcyl versus the 911? I would think the 911 would have the proportioning 'right' for our rear weight biased vehicles over the 944 which was more 50/50 if I recall correctly.

[Humble]

Actually that didn't make much sense to me either, until I sat down and looked at it. My 944 stuff came with the mc but i didn't use it at first. Instead I went with the beetle mc, which was a mistake, and soon swapped in the 944 mc. The 944 part was better (and I already had it) but still locked up the front tires pretty early. Recently I ponied up the cash to buy a new porsche 930 turbo mc (it shares brakes with the 944 turbo but the mc is split differently) and it's worked great ever since. Fronts still lock up first but I think that is a tire issue not a brake issue since I have to push it damn hard for this to happen.

[DORIGTT]

To make sure I understand you correctly..

Both worked, but the 930 version worked better than the 944 m/cyl for your application?

Was the install the same for both units?

[Humble]

Install was the same for both, I just bolted in the mc in place of the beetle part. Now I'm using 87 944 turbo disks, and 4 pot calipers all around so I'm not sure how well this setup would work with n/a brakes. The porsche 930 of the same year used the same brakes as the 944 so the mc matches the calipers. The 930 mc with 944 brakes is like hitting a wall if you jump on the brakes. The 930 mc also has dual brake light switches that connect exactly like a beetle mc (the 930 mc I bought even came with new switches).

http://i93.photobucket.com/albums/l44/humblewolf/Lucy/HPIM1575.jpg~original

[Steve C]

Hi

Do you know the bore of the 944 and 930 m/c? I don't think that the 930 used a brake booster.

Steve

[Jeza]

Because it works with the brake callipers as a system. The Beetle mc does not have enough volume to work well with the single piston sliding FRONT callipers from the early 944.

The 944 has a split bore mc, 23.?? for the front, and 19.06(?) for the rear. The rears work fine with the Beetle mc because the rear portion of the 944mc is the same diameter as the Beetle mc.

If you sit down and work out the front to rear ratio, you will be surprised, the 944 is not as bad as you think.

If you use a 911 mc, then use it with 911 callipers. You need to compare the mc volume and the calliper volume between the models, not just the master cylinder.
http://www.germanlook.com/Forums/showthread.php?t=2183

The later 944 4 pot setups are a different kettle of fish, and guys here have found the Beetle MC works with those callipers. I can't comment on this setup.


Cheers
Jeremy

[Humble]

I don't know the bore off hand but it is printed on the mc. I want to say it's 26mm and 20mm but I'll have to double check the mc to be certain.

[DORIGTT]

I've got the 4 piston 968 calipers that I plan to use.

[Humble]

If you know the caliper piston bores for front and rear i can tell you if it'll work with the 930 mc or not. I'd have to dig up the numbers for the 944t calipers again as well.

[Bugnutz]

the 944 master cylinder (thru 86, p/n 944.355.011.01) is 23mm front and 19mm rear.

[flat_iv]

Humble, what is the part # of the 930 master cylinder?

[Humble]

The part # I have is 930-355-011-03 and when I did a search I found it on pelican parts which is where I bought it

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=930-355-011-03-M4&catalog_description=Turbo%20Master%20Cylinder%2C%2 0911%20(1978-89)

As an update to my previous statements, I can lock up the front tires first with staggered rims and street tires. But when I toss on the race rubber it throws you against the belts and stops the car incredibly fast with hardly a peep from the tires.

[evilC]

The Porsche 930 M/C is a 23mm diameter (both pistons) model. The beetle standard one is 19mm diameter (both pistons) so it should be more 'powerful'. However, M/C piston size selection is very often down to the preference of the individual driver - power verses length of stroke.

Clive

[Humble]

What are the markings on the MC then? I thought those were the bore sizes :confused:

[effvee]

Hi, I have a 1302 that I am going to use the early 944 1985 single piston setup on. However I choose to use the front calipers on the rear also. So I will have all four wheels stopping with front calipers. Can you suggest a MC for me. I also have a 1971 Porsche book where the front calipers and rear are very close in sizing. I believe I need more than 19mm mc.
http://i86.photobucket.com/albums/k97/effvee/My%201302%20Affair/My1302Project.jpg~original

[Bug@5speed(US)]

Humble,

You brought up valide point about tires.. street vs race slicks.. which has to be factored into the equation.

What about pads.. I know on my street/track car I use to mix front and rear pads at times depending on the track and tire choices I had.. What is everyone using as their respective characteristics will have an impact on lock up also?


Alex

[evilC]

What are the markings on the MC then? I thought those were the bore sizes :confused:

They usually are but what are they, I can't read them off the photo?

Hi, I have a 1302 that I am going to use the early 944 1985 single piston setup on. However I choose to use the front calipers on the rear also. So I will have all four wheels stopping with front calipers. Can you suggest a MC for me. I also have a 1971 Porsche book where the front calipers and rear are very close in sizing. I believe I need more than 19mm mc.

The standard 19/19 dual circuit m/c is more than man for the job. However, I have heard that they give long pedal movement with single pot 944 fronts that could be down to the anti-slide spring that gives a twisting action of the piston body. This in turn means that if you have new pad on old discs or new discs with old pads there is a little extra bedding in to do to get the best pad shape i.e. a pair of matching shallow wedges. New pads on new discs should wear together so there ought to be no problem. It sounds as though you have about the right front rear balance assuming the discs are about the same size also. Don't think that because the m/c comes from a Porsche that it is intrinsically better than the VW one. With m/cs it is all about selecting the right size. Bigger m/cs usually mean poorer braking performance.

Humble,

You brought up valide point about tires.. street vs race slicks.. which has to be factored into the equation.

What about pads.. I know on my street/track car I use to mix front and rear pads at times depending on the track and tire choices I had.. What is everyone using as their respective characteristics will have an impact on lock up also?


Alex

Pad selection with full disc conversions with porsche calipers and discs will provide very high levels of performance in such a light car (around 2/3 the weight of a high performance Porsche) so the main problem will be to generate heat to get optimum friction. also, the cooling ability of the discs will quickly dissipate the heat that has been generated so it is better to select a quick i.e. low temperature pad. Any of the good quality pad suppliers such as Pagid will be suitable. I will be trying EBC Greenstuff on the front of mine.

Clive

[Humble]

They usually are but what are they, I can't read them off the photo?

The #'s on the MC are 26 and 20

What about pads.. I know on my street/track car I use to mix front and rear pads at times depending on the track and tire choices I had.. What is everyone using as their respective characteristics will have an impact on lock up also?

Pad selection with full disc conversions with porsche calipers and discs will provide very high levels of performance in such a light car (around 2/3 the weight of a high performance Porsche) so the main problem will be to generate heat to get optimum friction. also, the cooling ability of the discs will quickly dissipate the heat that has been generated so it is better to select a quick i.e. low temperature pad. Any of the good quality pad suppliers such as Pagid will be suitable. I will be trying EBC Greenstuff on the front of mine.


Clive is right about the pads, on light cars it can be hard to get them up to temp. Until now I've been running PBR metal masters on the race car but it's been an autox/hill climb car. In those events you can't really get heat into them, even with left foot braking. I've still got them on the car but I won't know if they're keepers until the first track event. Performance wise they bite pretty good initially, they're easy to modulate and predictable on release.

[evilC]

[QUOTE=Humble;70404]The #'s on the MC are 26 and 20

QUOTE]

I too would have thought that the numbers refer to the bore but the information I have been able to gleen is that the 930 ran plain bore 20mm pistons. It maybe that my numbers relate to a different (earlier?) version of the model in the same way that the 944 m/c changed to a stepped bore from a plain bore. I presume that the #26 is at the pedal end of the bore?

Clive

[Simon]

[QUOTE=Humble;70404]The #'s on the MC are 26 and 20

QUOTE]

I too would have thought that the numbers refer to the bore but the information I have been able to gleen is that the 930 ran plain bore 20mm pistons. It maybe that my numbers relate to a different (earlier?) version of the model in the same way that the 944 m/c changed to a stepped bore from a plain bore. I presume that the #26 is at the pedal end of the bore?

Clive

The 930 Turbo 78-89 is a dual circuit 23,8mm MC (930 355 011 03).
AFAIK it was used with a brake booster as well (1984: 930 355 027 00, >1984: 930 355 027 02)

[Humble]

I too would have thought that the numbers refer to the bore but the information I have been able to gleen is that the 930 ran plain bore 20mm pistons. It maybe that my numbers relate to a different (earlier?) version of the model in the same way that the 944 m/c changed to a stepped bore from a plain bore. I presume that the #26 is at the pedal end of the bore?

Clive


Actually 20 is by the pedal and 26 on the end. I thought I read somewhere that the 930 had the same 4 pot calipers all around but the piston sizes were different front to rear, the rear calipers being smaller.

[evilC]

Humble, The #20/26 can't be the piston sizes as the larger one would have to be at the pedal end! If the caliper piston sizes were smaller at the rear then it would have been more likely that the m/c would have the same bore size for front and rear circuit since the bias will have been controlled by the caliper sizing. It would be unusual for the manufacturer to have controlled it by both the caliper and the m/c (late 944 excepted). The 23.8mm (15/16") bore size does imply a power assisted pedal as it is quite large for non-servo assistance, which are generally </=19mm

Clive