Phil Raby

Er, heading says it all!

Cheers

Jeff Curtis

As a matter of fact the rears are the same style/size, but the pistons may be a bit different.

I do believe the front of a 944S2 are the 928S4 calipers though?? So they would be axial mount as opposed to having the "ears" to mount them to the spindle.

So, in that case who would want to install 964 calipers up front?

Ruairidh

....which - if they are pretty useless for other applications - brings us back to the question whether anyone is using 964 fronts in the rear (so to speak) as part of a big red front conversion?

Jeff Curtis

I have a few friends that are using the front 964 calipers in the rear with their BIG Red conversion. Cupcar has some pretty good MATH that states the pistons are too large for this scenario...I do agree.

My friend says he has no issues with the fronts on the rear, but he has HUGE two-piece rotors and uses a different brake compound on the rear.

SO, this suggests that the PO (he did not do the conversion, the PO did) found that there was too much braking at the rear. The bigger/better front rotors (Alcon?) may brake better up front, offsetting the rear effect...and the different compound at the rear is a lighter Hawk compound, I believe, this too suggests that there's too much braking back there!

I suggested that he change out his factory 45bar (it's a 1990, originally had two-piston rear calipers) to a 33bar, that way there's less surge pressure going to the rear.

Overall, I think it's an "OKAY" thing to do, but follow it up with a bias valve reduction, okay Pamela Lee??

Ruairidh

So the consensus here (having trawled through other threads) is that the issues with putting the 964 front calipers on the rear are (a) pads may fall out (the 964 rear rotor is 24mm while the front caliper want a 28mm) and (b) there are issues due to the size of the 964 front caliper pistons and, unless addressed, putting calipers with those size pistons on the rear with bog reds on the front screws up the front/rear braking balance. I do know that there is a dissenting opinion from Brembo on the balance issue but even if the correct view is that 964 fronts do work on the rear with a big red front that still would leave (a) to be addressed.

So, in summary: (a) can be addressed by machining the caliper to be narrower (at around $400 a pair?) otherwise pure physics will apply once your pad wears as the caliper/rotor combination is 4mm out of whack and (b) well, Jeff sets out what can be done there, unless Brembo's view is right.

Clear as mud? Sounds like a hassle to me - and perhaps best left to the racers?

kahuna

I think that Bill Verburg is the man you want to talk to

Jeff Curtis

Honestly, I don't believe that the 4mm rotor difference will cause any issues at all...really.

If you question that, and have changed pads before (I assume most of you have) then whip out a metric tape measure, etc. and "eyeball" 4mm - it's really not a lot. SO, for someone to say that this causes problems is somewhat ridiculous, that's just MY opinion.

NOW, if you scrub your pads all the way down to the backing plates (I assume MOST of you would NOT do that!) ...I still don't think it would be an issue, although your pistons would extend 2mm per side more than they would if you ran your pads down to the backing plates with your original rear calipers!

Make any sense?? Just using "idiot logic" there - I don't foresee an issue.

I had to rethink the scenario I pounded out in my last reply, my friend with the 1990 has his factory 45 bar valve, this was used on the C2 up to 1991, in 1992 they went to a 55bar bias valve with the four-piston calipers.

I may be mistaken, but the C4s all have a 55bar bias valve, unless they were a Turbo look, etc. - the bias might be different on those?

SO, if one that owned a 1992 and above C2 were to install BIG Reds up front, and moved the fronts to the rear, I would at least lower the bias valve to 45.

My first setup worked well with a 33bar...but that's me. When I changed to factory rear four-piston calipers (I have a 1991 - 45bar valve) the calipers turned a dark Army green at my first track event after the "upgrade"...they were getting HOT. When I returned home from my trip I installed a 33bar and never had trouble since.

For clarification: I had factory front C2 calipers and factory rear FOUR-piston calipers with the 33bar bias valve...everything changed when I went to BIG Reds.

MY ADVICE for 1992 and above 964 owners?? If doing a BIG Red upgrade, stick with your factory rear four-piston calipers (smaller pistons) and upgrade your bias valve to 60bar or eliminate it. Save your fronts for when you go to sell the car (with original brakes) or just as spares.

OR you can go through the hassle of swapping the fronts to the rear, my prediction is that you might have a little more bias to the rear than you need, so downgrade to a 45bar bias valve at that point and you should be okay.

My current setup is BIG Reds up front, factory C2 rear four-piston calipers and a 60bar bias valve, I use the same pads all the way around and brake like there's endless runoff.

Bill Verburg

I know little about the 944/951/968 calipers orr rotors. Mike Wacholtz at Prospeed would by the person to contact.

I do know that there is no front Brembo that should be moved to the rear because the pistons are way too big, it seems that we go through this discussion regularly, and no it is too far out for a p/v change to fix, dual m/c might but you are far better off getting the correct calipers.

The pistons do not need to pop out for there to be an issue, they need the support of the cylinder walls to remain true in their bores, get them extended far enough and they can and will **** in the bores, not pretty.

tonytaylor

Is the 964 caliper the same as the 3.2 caliper as I had 3.2 calipers on my S2

Jeff Curtis

Are you referring to the caliper that came on the Carrera 3.2??

If so - NO.

tonytaylor

Thinking about it the calipers on my S2 may not have been off a 3.2. I was told they were of a "carrera" so could have been anything really.
Sorry

Jeff Curtis

Hmmmm, maybe I'm mixed up and thought the S2 came with "928S4" calipers up front, I may be mistaken. I do know that the M030 optioned 968 came with those.

I also know that the calipers on your S2 were AT LEAST the same ones that are on a 964, although the piston sizes may vary??

The 3.2 Carrera calipers, unless it was a wide-body "turbo-look" Carrera, were just two-piston cast iron calipers, slightly larger than the ones that the 911SC were shod with.

...not sure 'bout dem aquatically-challenged P-cars.

tonytaylor

IIRC the mechanic told me the calipers were the same but had different size pistons. I did notice improved braking and was disappointed when I had to give them back.

Oddjob

86-88 944 Turbos, 89-91 944S2s, and 92-94 968s have the same brake calipers as each other. The caliper size and pad size are the same front and rear, but the mounting hole locations and piston sizes for the calipers are not the same front to rear. These are the same size front and rear as the 4 piston 964 calipers. But I do not know if the mounting bolt patterns are interchangeable between the 944 and 964 model lines.

88-89 944 Turbo S, 944S2 w/ M030 and 968 w/ M030 options have the larger 928S4 front calipers, the rears remain the same as the standard models.

No 3.2 Carrera or SC calipers or rotors will fit on any 944 that I am aware of. At least Ive never seen or heard of compatibility and it seems very unlikely.

With the piston sizes, I have seen various sized pistons on the same model year cars. The two 89 944 turbos (350 cars apart by serial number) Ive owned, have different sized pistons in the rear calipers. Ive driven both cars on the track and cant say I noticed any difference in rear pad wear or stability under hard braking from one car to the other. So Im not sure how critical the piston size is. I would assume if piston size does cause a problem, it can be offset by using a different proportioning valve.

Ive tried 18, 33, 45, and the 55 bar regulators, and there is a significant difference in rear brake power going between these valves.
Again in a 944 application, 18 bar will use little to no rear brake (rear pads last about 4 times as long as the fronts), and the 55 bar will cause rear lock up under even moderate track braking.

Bill Gregory

Jeff,

If you use Big Reds in front and stock 4 piston C2's in back, you can't possibly be using the same pad on both ends. Big Reds use a 132mm x 52mm pad vs the 98mm x 44mm C2/C4 pad. Maybe the same brand of pads?

We have different opinions on brake upgrades. My two cents are that there are three varieties of upgrades for our 964's:

1) With a 90-91 C2, upgrade the rear calipers to the 4 piston C4/92+ C2 rear. Along with this, upgrade the 45 bar bias valve to the 92+ 55 bar bias valve (964.355.305.10).

2) The S4 upgrade: The 928 S4 caliper has been used on the 964 Carrera RS, 968 with option M030, and the 993 C2, amongst others. The front calipers use a thicker 302x32mm rotor (928 S4 or 968 M030 fit in front), and with a small spacer can use 16" wheels. The front Carrera RS caliper uses the larger 322x32mm rotor. The 993/Carrera RS rear caliper uses the 964 stock size rotor (299x24mm) however with larger sized pistons. Recommend upgrading both front and rear for best balance.

3) Big Reds: From the 993 Twin Turbo, with larger 322x32mm front and 322x28mm rear rotors. These use larger brake pads and require 17" wheels for caliper clearance.

When mixing and matching various combinations, you're asking for an out of balance braking solution, which as Jeff points out, becomes very apparent at the track. Porsche is generally industry leading with it's braking solutions. To keep things in balance, I recommend the three flavors of brake upgrades outlined above for our 964's. Bill Verburg has an excellent web site with details of the various Porsche brakes at http://www.pelicanparts.com/MotorCity/wmv/brakes.htm