Hey all, my team has now completed 1 event with our ChumpCar:

http://sphotos.ak.fbcdn.net/hphotos-..._6353087_n.jpg
(www.chumpcar.com - budget road racing)

however, we have a problem. At low speeds, during and after hard turning (while navigating the paddock, and pits, etc) our brake pedal looses pressure, goes to the floor, and takes multiple pumps to get pressure back.

Some background on our brake setup:
..GSR booster and REBUILT 1" master cylinder (we have now gone thru 3 MC's - 2 junkyard and now the professionally rebuilt one - and have decided there is no way the MC is the problem)
..Stock prop valve
..Stock brake lines everywhere
..Acura legend single piston front brakes (we rebuilt ourselves with rebuild kit, and had the brackets shaved to work with civic EX brake rotors)
..Integra rear disc swap, nothing fancy there.

That being said, we see no signs of a leak anywhere, the resivoir isn't losing fluid... we're stumped.

Somehow I am tending towards the idea of the front caliper pistons being forced back into the caliper body when we are turning at low speeds, causing the pedal to need to be pumped to get them back out. Am I crazy on that?

I really need help/advice/suggestions. It doesn't really affect us much while we're racing, but it is a very unnerving problem. Thanks in advance!

 

stock prop valve in a civic that came with read drums. now you are using rear integra disks...try changing the prop valve to an integra one for a start? just a suggestion..

the only way those front pistons will compress back in under hard turns is if you have really messed up front wheel bearings..?

is the brake booster a integra one or the stock civic one?

 

I really don't think its the prop valve. If that was malfunctioning I'd just think that the brake balance would be off. Why would it cause a loss of pedal pressure? The brake booster is from a GSR.

Any other suggestions?

 

could the booster be bad? or maybe the check valve in the line going from the manifold to the booster?

although it does sound like a master cylinder problem but since you replaced them a few times i cant imagine all those MC's are bad?

could the fluid be boiling? any air in the lines?

 

Wanted to check-in and see if this problem was ever solved. I just ran into the same issue on my car with a fairly similar setup.

 

Yes, it was solved. Stupid mistake caused it. The front forks were installed backwards, so they would hit the calipers and force the piston back in, which meant you had to pump the pedal a bit to build pressure again.