Hard Brake Pedal...sometimes

[Marke]

So at a few of the Auto Slalom and Solo events this year my brake pedal got hard and the car didn't want to stop very baddly. The next time out, no issues. Car stops on a dime for a few events and then out of the blue it happens again. Cycle goes like this for awhile.

Thought it was the brake booster, but that wasn't the issue. Vacuum reservoir was cracked and I fixed that, but it did it again after ward. The ABS actuator I bought new, a few years ago when the old one started leaking.

I flush my brakes fairly regularly in this order. Rear left, rear right, front left, front right, ABS front and ABS back.

Is it possible I have air bubbles in the system?

Any ideas??? Or better yet, know exactly whats wrong because you had the same problem?

[markc32]

check caliper my friend...

[bellis_GTR]

seized caliper? or one starting.

[markc32]

also the master cylinder...not doing its job

[GTRADDICT]

bubbles would make it soft.

[Marke]

Checked out the calipers and one of the dust boots is obliterated, so there is a very good chance the piston is binding. I was going to rebuild them any how.

Master Cylinder is working fine.

Thanks for the input.

[Marke]

So I have had the calipers rebuilt and out of the 2 auto slalom events this year, I have had the pedal go hard once out of 18 runs. Need to figure this out before I do my first Solo Sprint/Time Attack event. Any diagnostic tests any one can think of?

[Bossman]

Your pads may not be sliding freely on the two long bolts/pins due to corrosion and/or heat expansion. Make sure the holes on the pad's backing plate is clean and big enough to slide through those bolts. I would re-drill the holes to clean then up and use some sand paper or steel wool and polish the bolts. New bolts would be better but I don't know how hard it is to find these long bolts.

[Marke]

I swap the pads fairly frequently and the bolts travel easily in and out. Everything appears to be corrosion free. The holes in both sets of pads I use are more than adequate in size.

[amnash]

if your fluid wasn't changed when it was supposed to be then the internal seals could be gone on your master cylinder, you can check by using a mirror to look at the bottom of your brake booster. if you see fluid dripping down or a rusted trail then its the master.

[Bugsly17]

are you left foot braking?

if your car is boosting, and you press the brake pedal, it will be hard. your brake boosted runs on vacuum. when the car is boosting, that is the opposite of vacuum.

In that little hose that goes from your intake manifold, to brake booster, there is a valve. when there is vacuum in the system(no boost, not on the gas), the valve is open, and the brke pedal will be SOFT(normal brake pedal). When you are boosting, the valve closes. there will be no brake assist when your turbos are spooled. No brake assist=hard pedal.

Possibility.

[amnash]

^^ theres suppose to be a check valve in that line?? mine just has a hose and thats it. not that essential?

[Marke]

are you left foot braking?

if your car is boosting, and you press the brake pedal, it will be hard. your brake boosted runs on vacuum. when the car is boosting, that is the opposite of vacuum.

In that little hose that goes from your intake manifold, to brake booster, there is a valve. when there is vacuum in the system(no boost, not on the gas), the valve is open, and the brke pedal will be SOFT(normal brake pedal). When you are boosting, the valve closes. there will be no brake assist when your turbos are spooled. No brake assist=hard pedal.

Possibility.

Hmm... you could be on to something there. Maybe the vacuum reservoir needs to be bigger?

amnash

^^ theres suppose to be a check valve in that line?? mine just has a hose and thats it. not that essential?

I know the one you are speaking of and I replaced it with a new one, thinking it might be the problem. I was looking at the line that goes from the vacuum reservoir to the booster and noticed that it was looking a little flat and felt soft. I was wondering if it was getting sucked closed for an instant there by causing vacuum loss?

I felt the pedal go hard again today at auto slalom, but it was only under mild braking, but it was after a series of short brake stabs I used to plant the nose for some sharp turns. As per usual it was only that one time it went hard.

[Marke]

So I have discovered I can induce the hard pedal with constant left foot braking. Is this normal? Am I really running out of vacuum that fast? What does it mean?

[Marke]

So after doing some research, I have discovered that it is pretty common for high performance turbo and supercharged cars to not produce enough vacuum to run the power brakes.

So now I am thinking electric vacuum pump. If they come small enough I could put it were the vacuum reservoir is. Any body else here do something like this before and to what result?