friend has a weird problem on his 91 crx si with stock brakes. The pedal starts to go the floor on him in the afternoon and whenever the car warms up to operating temperature.

I took a quick look at it and I'm pretty much no help. We just checked to make sure there's no leaks anywhere. Did see any at the calipers on any of the wheels, nor at the prop valve or at the master cylinder. It doesnt loose any fluid either.

I had him crank the car up and push the brakes while I had the cap off of the reservoir. Normally with good brakes, you'll get fluid squirting up and out but absolutely nothing happened...

Also noticed that if you just let the car idle it will idle rock steady but if you pump the brakes it will idle up a few hundred rpm and then settle back down after a few seconds.

makes me think that the little check valve in the line from the brake booster to the intake manifold is bad but that cant be whats causing this could it??

any help would be appreciated since this is his driver and it's dangerous without brakes in atlanta traffic....

 

Well it's not the break booster if you hit the breaks and it Idles up, so it has to be your master cylinder I'm pretty sure.. My mustang used to do the same exact thing and It was the master cylinder 3 times! But if I'm wrong then I have made my best efforts

 

ok, so the check valve from the brake booster should let it idle up like that??

 

yes it should cause it to idle up about 200-400 rpms