It has to be leaking into the vacuum chamber (Booster). It sounds like the replacement master cylinder is also bad. I'd pull the MC and look for a leak.

we have all decided that this is the only logical explanation. We never could get a good brake pedal after we put the master cylinder on. We thought that we had not bled them enough, but we kept on bleeding them and never did get firm pedal.

This saga will continue after work tomorrow.

Im leaning on that it's in the boost part of the master cylinder also. But i have a couple of questions for Mary concerning the bleeding of the the lines.Prior to installing the master cylinder, was the master cylinder BENCH BLED before bolting it on the firewall? Also were the wheel cylinders rebuilt/replaced at all?? Now if after you did not find brake fluid in the booster, Check the brake drums, they can hold
quite a bit of brake fluid without leaking on the ground. especially if ya had to beat them off a bit. just trying to help out.

ZIM

Zim, master cylinder was bench bled
wheel cylinders were not replaced (had been done previously)
4 wheel disc brakes.
plan on doing what bill h suggested about the brake lines to the master cylinder. This is a "spare" car so no hurry to fix, just curious to see if we can fix it before sending to shop.
1990 model and I have had it since 1994, it is really fun to drive.

quote:

Originally posted by Mary Ray:
4 wheel disc brakes.

OK, that eliminates the load sensing and proportioning valves I mentioned as possible leak sites.

Have you ever seen a cloud of white smoke, perhaps when sitting at a red light then taking off? My Chevy truck did that when the booster went bad and the fliud leaked back through it and got sucked into the intake through the vaccum lines. Finally figured out that's where the fluid was going in my case. It blew out soon after I installed a new master, and I was told that's common, due to increased pressure from the new MC. Brakes were terrible till I replaced the booster.