As background, my Fiero has C5 13" brakes in the front and C4 12" in the back with a SSBC prop. valve and distribution block with the stock master. The SBC has had a GMPP hot cam at the same time but I've had no vacuum issues with it. The brakes were done 3 seasons ago and I've have no problems with them whatsoever until now.

Suddenly, the brakes went from feeling normal to suddenly when I press the pedal its REALLY firm and it feels like I've got 1/3 the braking power I usually have. If I really lean on them, I can get the front tires to lock but it needs a TON of foot force, they lock just before the car actually stops and the pedal really doesn't move much. Then the next time I hit the pedal they feel normal at initial bite and then get really firm. Basically, it feels like the booster loses vacuum and the brakes are working manually. I checked my brake vacuum line last night with a mighty-vac and found a possible loose connection back at the filter so I used hose clamps on all the connections at the motor hoping that would solve it. After that I could pull about 10 inches of vacuum (no more) and it would hold it. Drove it today, same thing; sometimes feels fine but otherwise the pedal is really stiff without much brake power. What is causing this? Master? Booster? Prop valve? I'd like to do a track day this summer but there is no way if I keep losing power brakes. . .

A side note - When I first did the brakes, I plumbed in a TCI line lock selenoid just for kicks. I never got around to wiring it until this summer and it seems to work the way it should but I'm wondering if it has something to do with whats happening or if its just a coincidence. Since it started happening, I unplugged to wires to the LL so its disconnected again but the problem persists. At first I thought the selenoid was blocking off the front brake line which was causing my stiff pedal and low braking force but I can still lock the front wheels so there is pressure getting to them.

Any thoughts?
-Tim

I would suspect the brake booster, or the general lack of vacuum from your camshaft.

While going 70, then let off the gas with the clutch engaged and the transmission in the highest gear (engine braking), when the car slows to 60, hit the brakes and slow to 50 and release and then hit them again and slow to 30. The engine braking should provide ample engine vacuum for good brake performance (regardless of camshaft). If this test doesn't result in good brakes, then you either have a brake booster or some other mechanical issue.

While going 70 mph, kick in the clutch, let the engine idle for a couple of seconds and then tap the brakes a few times (not trying to stop, just bleeding off any excess vacuum so all you have is idle vacuum), then once you coast to 60 hit the brakes to slow to 50 and release them, then hit them again and slow to 30. If you notice less braking performance vs. the first test, you most likely have an idle vacuum issue.

[This message has been edited by fieroguru (edited 07-15-2011).]