I just picked up a 94 Jetta, and among other things, it has a strange brake problem. Sometimes the brakes work OK, but if I hold the brakes on, the pedal gradually sinks to the floor. Other times the pedal goes to the floor without resistance. I can bleed the system, and get a lot of air out of both rear cylinders. Just when the pedal feels like its working, it goes to the floor and I get to start all over again. There are all new steel lines and there is no sign of leaking anywhere. The master and both calipers had been replaced recently. I thought it might be a master, so I replaced it with one from a donor car that had good brakes, without improvement. My next idea is to bypass the proportioning valve. Any suggestions or ideas appreciated.
Paul
there is a lever on the proportioning valve that has to be actuated and then locked into place when bleeding the brakes. i have the same problem as you, and i didn't do this, but bled the brakes very well. i'm going to try this and see how it works. i still need to replace a stuck wheel cylinder though...
