I hope this is last time that I have to bother you fine people. It's me again, the 1983 242 ti owner ... yeah the one with the brake problem.

So here is the update. I took the brand new master cylinder that I just purchased off of the car and replaced it with a known working one off of my other car (1983 244 ti). We bled the brakes again (I know I am doing this correctly). Absolutely no air comes out of the bleeder screws anymore and I re-bled the MC as some of you suggested. I am confident the brake components I replaced (calipers, pads, etc.) are installed correctly (have done it many times). We bled the brakes with the car off and the pedal felt great (like old times!). I thought we finally had it. But as soon as I started Greta and pushed on the brakes the pedal slowly sank to the floor. It doesn't quite touch the floor but it comes very close. We tried bleeding it once more ... pedal felt good with the car off ... turn car on ... pedal sinks to floor.

What on earth could be causing this? I am absolutely baffled and am truthfully becoming very discouraged. I believe Jessie mentioned that it may be the pressure differential warning valve. If this could be a problem how do I check it and how hard is it to replace? I was also wondering if the brake booster could have something to do with the problem. After all, the brakes feel good when the car is off, but as soon as you turn it on things get ugly. Is there any other brake component that only operates when the car is on?

Thanks for your patience and your suggestions.

Regards,
Greg