I have experienced a soft or non-existent brake pedal during every one of the last six race weekends followed by a leaking rear (only the rear) brake caliper. It has been on the right rear 5 times and left rear once. All four rotors were replaced, installed new calipers at the first leaks and then rebuild kits the next leaks, new flex and hard lines on both sides in the rear, new master cylinder and of course a ton of fluid flushed through the system. I run PFC 97 pads on all four corners.

Prior to converting the engine to Euro spec in 2011 I never had a similar problem in five race events. I have puzzled over this with my mechanic who basically says I don't know how to drive, and while he may have a point, I think there has to be something else going on here. I did have a bad left rear bearing the one time that caliper failed but am not sure if that can be a contributing factor. If it was a simple matter of over braking I would think it would be the fronts that would overheat, destroy the seals and leak, not the rears.

I would appreciate any insight the collective wisdom of the board can offer and am ready for the inevitable abuse that comes with said advice.

 

I DE'ed and raced SC's for years and leaking rear calipers were always an issue. I rebuilt them regularly and replaced them from time to time to no avail.

Based on feedback from my mechanic and others, I believe it is a heat issue from the engine and exhaust that prematurely aged the dust covers and o rings.

I didn't see it every weekend like you did, so maybe your bad driving is amplifying the issue. What rate are you going through pads? Even with the issue I was still going through 2 fronts to every 1 rear.

Listen to your wrench - brake less and you won't have this issue as often!

 

I take no chances with our pitiful brakes:

Castrol SRF fluid
Brake bleed before every weekend
I rebuild the calipers every other weekend (seriously)
Very low threshold to replace pads and rotors
Pagid yellows (front) and blacks (rear). These are awesome pads.
Dual inlet front rotor cooling plates (air from bumper AND control arm scoops)

 

Thanks. I have not had any issues with pad life, and get about two race weekends out of the fronts and three to four out of the rear. I change them when they are 60-75% gone. The problem does not seem correlated with how much pad is left.

 

Frank how often are you replacing your rotors? Those rears I saw on your car in Atlanta were way past their useful life and would definitely lead to a soft pedal. When that much material is missing from the rotor there is only so much heat it can dissipate.

 

Could overfilling be an issue?

 

I ran this same setup on my 83' SC (D Stock). In two years of torturing it, mostly at Sebring, I experienced zero leaks front or rear. As it's the only thing that you didn't mention as having been replaced, perhaps MarkM has a point with the rotors.

 

I replaced all four rotors after RA and before Watkins Glen and damned if I didn't have the same issue; pedal goes to the floor in T3 during Friday practice at VIR, so I bled the fronts and replaced the pads because the inboard right pad (put on pagid orange for the first time at the Glen) was twice as worn as the outboard, and then I find a puddle of brake fluid under the right rear on Saturday morning. Rebuilt the caliper and the brakes were then fine for qualifying and two sprint races.

 

I assumed max fluid dissipates the heat better but maybe not.

 

Thanks for the ideas Jack. I have not rebuilt or replaced the front calipers in three seasons so I will definitely do that and bleed with Castrol SRF for Mid Ohio.

 

That is frustrating stuff Frank. I remember losing confidence in my brakes on the carrera. Not fun.

 

Where are you getting your rebuild kits? What brand? We run SC calipers on the back of our car and haven't had any trouble in 5 years.

 

Maybe there is a mini hole in a brake line so under pressure it lets go a little. Maybe its a hard line or something still seems it heat esptecially with your wheels anodizing turning gold. Or your brake is sticking creating heat

 

Frank, have you tried leaving the brakes under pressure over night to see if you can find a leak? Use a pole of some kind wedged in the driver seat pushing the pedal down. If there is no leak then it's heat I would think.

PS - don't use the brake bleeder for this as it will leak air very quickly and you'll be even more flummoxed.

 

I don't think your two issues are as related as you think. The leaking is an issue, but your soft pedal may be due to how long you let the pads go.

Your pad wear/ratio is a good sign that the overall system is balanced for an SC. Make sure the pads are consistent when you take them off. The inner and outer pads should be almost identical in thickness, if you have a caliper springing a leak, the pads will be uneven.

The brakes themselves are 30-35 years old so any combination of piston or caliper wear, which may not be noticeable to the eye, can be out of spec. Have you replaced the pistons?

We swapped out several sets of calipers/pistons/rebuilds until I found 2 that were good. Some folks have also used heat shielding on the headers used to keep the rear assembly cooler.

I have always noticed that any pad at 50% fells soft, so if you are going to 25%, then you are going to feel a soft pedal no matter what you do.

You are probably over braking, as all of us club racers do. Try and follow some of the SC/Carrera class leaders and learn their techniques, you will be amazed to learn how little they abuse their brakes.

Think about this. You start an enduro with well used pad, but they feel good because you just bleed them. As the race goes on they get softer and softer, so you adjust your braking zones. You brake earlier, but not as hard and are more aware of your braking and balance late in the race. Now, check your lap times. Did they change significantly? Probably not. In fact, some of my best laps are late in an enduro because I was braking less and more smoothly.

Braking is not about slamming on the brakes late, but how early you can release them. So late in a race you may 'let go' sooner in an effort to save the last bit of brakes and you find out you didn't need them as much as you though earlier on. This was a long learning curve for me and I needed to have complete confidence in the car at all times.

Now that I switched to a newer car I have the same learning curve all over a gain for some reason. Maybe its just because I have become a headcase.