SSBC disc brakes - heat soak???

[groho]

Whelp, finished up my 66 coupe and now autocrossing as scheduling and commitments allow. I'm having a problem that has me stumped and wanted to get your feedback. Running manual brakes, SSBC disc's up front, and drums in back. Pedal is firm and high, street driving works and stops as expected. After I've completed an autocross run and have a 15-20 min break before the next run I'm come back to the car and notice my brake pedal is low, almost to the floor. Pump the pedal a few times and comes right back to the top and stays there. I run the course, all is good, get off course, 15-20 min later, same problem, pedal is low. During normal street driving the car is fine without issue. The only thing I can think of is I might be overheating the rotor and as it expands it pushes the piston back, and once it cools down I have all that space to make up and reseat the pad. The other option is maybe an air bubble in the M/C? Any ideas would help.

[dontlifttoshift]

Is the pedal ever low during a run?

Do you have a 10lb residual valve to the drums?

Are your wheel cylinders leaking? You may have to pull back the boot to see.

[groho]

no 10psi R/V, the one I installed leaked like a sieve so I removed it. Running DOT4 and SS braided lines. I've made sure the rear shoes are adjusted properly, and tight. Again, normal driving the brakes are fine, pedal is high and firm. During and immediately following the run, the pedal is fine. The runs from last week were 75 sec's overall, 16 turns and one 5 cone slalom, at least 3 very hard braking zones, not a problem. Its when I park and stretch after a hard run come back to the car some 15-20 min later i always find my pedal down. It pumps right back up to the top, and go for the next run, does fine, finishes fine, did 4 runs that way. Did an under car inspection yesterday with 0 leaks anywhere. Have to pull the wheels for some suspension mod's, will take a closer look. I know this system cuz I put it in, but also have never raced before so it has me stumped. If someone can give me an idea of where to look, or what to look for would be helpful.

[dontlifttoshift]

Drum brakes require a 10 lb residual valve. Get one that doesn't leak and install it.

[groho]

Found the problem with the R/V, the tube flare was sharp and scratched the seat of the fitting inside the R/V. $1 part for a new fitting, and a new flare, problem should be resolved.