cpa7man

iTrader: (2)

The car with the brake issue is a first gen race car running 23x9.5x15 slicks. The brakes are stock 12a, fairly new front rotors and Hawk Blues. Motul brake fluid, and about 95 degrees out.

I have run this car all year and have never had a brake issue before. Today I lost my brakes in 2 different sessions. The first time the brakes left they did so without warning. Pedal feel was fine until I went for the brakes at the end of a long straight and the pedal went to the floor. I was at a local track with long runoff areas so no big deal, just got a bunch of dirt/grass in the car. After cool down normal pedal feel returned, and we bled the brakes. Next time out same thing, again towards the end of the run session the pedal went to the floor, this time I noticed some loss in pedal feel before failure.

The question, is this just due to brake fluid boiling or should I suspect the brake master as well? I've never even had fade before with this car.

BTW: I'm going to do a full flush before my next event.

Any input is appreciated.

RoadRaceJosh

Bummer drag. If the brake pedal wouldn't pump up I'd say you're boiling the fluid. The fact that after cool down the pedal returned supports this. I'd examine your brake ducting. Otherwise you may be getting excessive piston retraction from warped rotors or loose wheel bearings. In any case you need to do an extensive check of all 4 corners. Make sure you don't have an axle walking out either. Oh, you didn't say if you have drums in the back. If you do it's also possible to pull air into the wheel cylinders if there aren't expanders inside the cups in the wheel cylinder.

cpa7man

iTrader: (2)

Thanks for the input, car is going up on the rack for a full check over in the next day or two. Car is 4 wheel disk.

DamonB

Sounds like classic fluid boiling. When was the last time the fluid was replaced?

Pat McGroin

If it's been a year and you've been tracking the car definitely opt for a full rebleed.
You might be at the wet boiling point which is over 100 degrees difference from Motul's dry boiling point.

cpa7man

iTrader: (2)

Thanks guys for confirming what we suspected. I just never had the brakes go from there to not there that quick. I bleed my brakes between most events but it's been almost a year since a full fluid chage out. I'll suck it out and do a full fluid change.

RoadRaceJosh

A year? Oops. Brake fluid on a race car can easily be an every event service item.