Just bought a 69 Z28 which has had everything replaced in the braking system, ie., lines, master cylinder, booster, etc. When the pedal is depressed once, the brakes work fine, but if let up and engaged again, the pedal goes very low and is hard to get any braking. This car has only the front power brakes and drums on the rears. I was told that this is a common Z28 problem, due to the 30/30 cam which doesn't produce very much vacuum. It also has stainless steel brake lines. Any thoughts?
It is not common on mine. Sounds like when do the first the master cylinder is not reloading with fluid for some reason to me.
Read these: http://www.camaros.org/forum/index.php?topic=2938.0
and http://www.camaros.org/brakevalve.shtml
See if any of that info helps.
Steve
Sounds to me like you are losing power assist. I would check that the booster is holding vacuum after the engine is shut down.