I have a 1991 964 C2 which I track regularly. Since I purchased the vehicle, whether on road pads or track pads, it has absolutely no initial bite and the car feels like it won't pull up. Once the pads are warm it is a little better however, on the track, I get a dropped pedal after two hard laps and loss of retardation ability. The pedal will then pump back up on cool down in the pits. The pedal does not drop on the road or when holding constant pressure on the brake pedal so i am assuming my master is ok.

I have tried the following.

Many different road and track pads.

Road. OEM Textar, Ferodo 2500, Porterfield R4-S, Racebrakes RB-74 (Australian product)

Track. Ferodo 2500, ferodo 3000, Pagid Blue, Pagid Black, Project Mu

All had the same no bite issue, Pagid black were best for the track but still had a dropped pedal and needed to nurse brakes a bit after 2-3 laps, especially at high speed tracks like Phillip Island and Sandown out of Melbourne.

I have bled brakes numerous times, run AP racing fluid, have upgraded the rear small brakes to later 964 rear brakes and still the issues persist.
I have upgraded to slotted discs front and rear.

ABS lights don't come on and all checks are ok.

Next step is braided brake lines but i can't see that this will solve the bite and the fade.

Porsche usually have the best brakes in the business, what is going on?

 

Makes no sense. Always run Pagid orange with ATE Blue or Motul on the '92 C4 and both RSA's. Laguna into T2 is our brake eater in Northern California, and I've rarely run into a soft pedal.

I did fabricate brake scoops that hung off the control arms on the RSA racer, but I didn't see much of a temperature difference.

Only further suggestion I have is liberal use of high temperature paint like this:

http://www.pegasusautoracing.com/pro....asp?RecID=862

Once you definitively determine your operating range, it should become more clear what steps to take.

 

I've used a number of those pads you mention with great results. Initial bite with the textars on the road is great and the pagid greys I use on track are even better with the higher temperatures involved. I use solid OEM rotors and don't get any sign of a soft pedal in 10 lap stints.

The only thing from your experiences that draws my attention is that you use AP racing fluid. Which one? The reason I ask is that you'll see in this link that only the second two (type 551 and type dot 5.1) are specifically recommended for combined brake and clutch systems like we have in the 964.

http://www.apracing.com/info/info.as...uid+Details_48

However, someone else might have used the other two types and I'm talking rubbish

p.s. I use Castrol Response super dot 4 and flush the lines with a litre after every 4 trackdays.

 

http://www.wilwood.com/pdf/ds213.PDF
http://www.wilwood.com/Products/006-...BLCV/index.asp

 

Dear Jimjacqmx5

Have you considered the caliper(s) seals as they are the closest part to the heat source and heat expansion?

Bill

 

If the pedal goes soft it is generally from over heated brake fluid

* cool the pads and rotors as much as possible
* lose as much weight as is possible
* use fresh high temp brake fluid, there is a wide range of available boiling points and a wide range of prices, a great yet reasonably priced bf is Motul RB600, currently factory fills are Endless RS 650
* use track pads w/ a heatbarrier in them most modern pads will, Pagid yellow and black are both very good choices, Pagid Orange is an out dated choice Blue is more of a street pad.

 

Right. I should have been more clear of my past tense using them. I think the last set of oranges I bought was in '04. But it's what I DID use from '98-'04 with the C4 and RSA #1, and then as leftover stock with the current RSA until maybe last year.

Also, when we consider that Porsche has the "best brakes", a lot of that is just pure physics considering where a 911 has all its mass!

Ultimately, this shouldn't be tough to solve as we race 3.0 and 3.2L cars with those tiny A and M calipers in stock classes.

 

Thanks so much for all your replies.
My feeling initially was that it was an overheating issue as mentioned and that is why the pedal went soft.
However, as many of you have mentioned, you never have issues with this and other guys racing here with 964's don't have this problem either and they are running more street focused pads.
I have used both Motul and AP racing brake fluid and that hasn't helped.
I'm with the darth vadar dude in that it must be a hardwear issue.
I was thinking master or something in the ABS unit or the calipers as the brakes just feel unbelievably bad and the pedal is totally wooden. the car has no bite in the brakes and just doesn't want to pull up the way i believe it should.

It feels like realy bad glazed discs but when i tried new discs it was no better.

All I know is that when I'm trying to stop from 230plus km/h into a hairpin at a fast track like Phillip Island I am not reassured by my brakes!

 

When flushing brake fluid through did you bleed both sides of each caliper? Just thought I'd mention it as not everyone realizes that there are two bleed nipples per caliper.

 

Dear Jimjacqmx5

"car feels like it won't pull up" ; "loss of retardation ability" - Not sure what these terms mean, please explain.
"The pedal does not drop on the road or when holding constant pressure on the brake pedal so i am assuming my master is ok." I wouldn't rule out the master, the fact that the problem doesn't occur during normal braking leads me to believe you have a heat issue which only occurs during heavy braking while on the track. The common components to the 4 brakes is the master and the proportioning valve. Do you feel the car has front bias or does it feel like the rear brakes are doing a lot of the work. How does your front and rear pads wear compare? Does your ABS work? When bleeding the brakes it is important not to have any air in the system. Agitating the brake fluid container (i.e. shaking it like a spray paint can) will introduce tiny micro bubbles in the fluid which are nearly impossible to remove and tend to expand with heat, producing some of the symptoms you describe as well as a spongy feel to the brake pedal. Not sure of the fluids you've tried but silicon type brake fluids also produce a spongy pedal.

Bill

 

"run AP racing fluid"
http://www.apracing.com/info/index.a...Brake+Fluid_33

 

Have you checked the vacuum assist system ?
It kind of sounds like your brakes are un boosted .
The C2 has a vacuum boosted brake system .
If the vacuum system isn't working you will feel
"it has absolutely no initial bite and the car feels like it won't pull up."

I would do a little test , I would clamp off the vacuum line and then take the car out to a very safe place and see if the brakes feel any different .

http://www.pelicanparts.com/cgi-bin/...0%281990-94%29

 

Do a simple caliper test to make sure your caliper pistons aren't sticking in their bores. After removing your pads, individually push each piston fully back into their bore. The effort you exert on each piston should be smooth, consistent and offer slightly higher initial resistance before sliding smoothly back into place. If your efforts are inconsistent from piston to piston (or even from caliper to caliper) it indicates that the dust boots have been compromised (tiny nick holes from using bad technique or the wrong tool) and grunge collected on the bores/seals. The solution (since it ain't gonna get no better with time) is rebuilding (there are kits available, but what a PAIN!!) or caliper/s replacement. But it's a pretty easy test that's certainly appropriate considering the problems you're experiencing. I had somewhat similar brake problems and solved mine in precisely this fashion. Good luck.

 

Jim,

I just went through similar issues with my brakes and this is what I found. You can also do a search in the 964/Racing forum under my name and find my past posts where I was dealing with similar symptoms.

1. Brake fluids - be very specific and careful with these. Not all 'racing' brake fluids can handle the temperatures that the 964 puts out when really standing on the binders. Many moons ago I converted from the Blue/Gold to Castrol SRF because of softness in the pedal and have never looked back - don't skimp in the brake department. For example the AP Racing 600 fluid has a dry boiling point of 300 and the Castrol SRF has a wet boiling point of 518 - very different levels of capability when dealing with heat. Wet boiling point is always less than the dry boiling point and the measurment of most interest.

2. I have tried many different pads and the only track pad you list that I would say is up to the track task is the Pagid Black. I tried Hawk Blue and PFC '97 on my 964 and was having some soft pedal issues, so after urging from a number of folks on Rennlist and a couple others outside who I trust, I switched to the more expensive Pagid yellows (29s) and didn't have any more soft pedal issues - even when pushing harder and running faster than I had ever before. I am pretty sure the blacks would be fine (I've used them before), but they will produce more heat than the yellows because of their stronger bite.

My suggestion is if you really want to solve this issue, start with really good brake fluid and do a full brake fluid flush (not just a bleeding). I think you will be surprised what good fluid can do for your brakes. For the track, combine that fluid with a good track pad - Pagid Yellows is what I would recomment for obvious reasons.

Let me know how it goes and good luck.

-Skip

 

Still confuses me. I like the recommendation to check the vacuum booster, but that's going to be pretty obvious just tooling around town approaching a stop sign. I had a similar problem with the '92 C4 and its hydraulic assist; the reservoir would run out of fluid braking uphill, T3 at Willow specifically.

In rereading the original post, if the flex lines are original, yeah an inner collapse could keep a caliper stuck. But as I said initially, put some temperature paint on the rotors and you'll see what's what pretty quick.

To show how unpredictable pads are car-to-car, I've got some leftover Hawks on the RSA now, Blues or something in front and their street pad in the rear. Probably have 2-300 track miles at speed with a wonderfully hard pedal even after a full session.