Bad booster, Master Cylinder or ...?

OK, so I changed out the stock '94 booster and master with a stock 2000 booster and master setup. I also replaced the old vacuum hose at this time.

Everything bled out OK after the swap and I adjusted the rear brakes while I was at it since the e-brake needed to be pulled all the way and then some to engage.

The first booster I had in was bad. You could hear it hissing in the cab, and it would then get the rock hard pedal.

I swapped in another booster, a re-manufactured one from AutoZone. I now get the hard pedal and brakes clenching up (eventually locking up) about once a day. If I pull the master from the booster I can hear the vacuum break and then the system works fine for another day.

I have replaced the check valve, it had a leak when you blew into it slowly. But the problem still persists.

So did I get a lemon of a booster, or could there be something else wrong?

I assume you have the appropriate MC for the booster your using? And have you checked the booster-to-MC push-rod to insure it's not not touching the MC? You should have a hard pedal with the engine off, then while still pressing on the pedal, start the engine. The pedal should drop, indicating a good booster.

Yes, the MC is also from a 2000 XJ to match the booster.

I don't believe the rod is touching, I'll check the next time I have to separate them.

The pedal is hard, or can be pumped (once or twice) to hard with the motor off. Sometimes it works fine and the pedal drops, othertimes the pedal stays hard and the breaks are fully engaged.

The rod is not touching.

I'm pulling the booster and getting another one today. Something is fishy with it. I know it's holding vacuum. When I pulled the check valve it released pressure in the system, so I also know that part was good. I'll throw the one that came with it back on since it's shot as well.

Hopefully I'll get a good one this time around. The good news is that I'm getting pretty proficient at getting the booster in and out of the rig.

Keep us posted on the results.

FAWK :smsoap:!!!!! The booster isn't/wasn't the problem.

Got the new booster in this afternoon and ended up back at the same problem. The symptom acts like a bad booster. The pedal started out fine. Pumped it up, started and it went to the floor.

Tried it a few more times and it was fine, then as I was driving after tapping the breaks to slow around a corner the brakes slowly started engaging with no pedal pressure applied. Pulled over as the brakes fully engaged, got out pulled the master and released the vacuum. Tightened everything back up and it was fine for the rest of the day.

I'm at a loss for what the problem may be. At this point I may just end up going back to the stock '94 booster and master setup. I love the added braking power I get from the '00 setup, but not when I can't drive it.

OK, where do I get my sign? :dunce:

Just nomiate me now for tard of the year. I wasn't feeling any resistence since the rod was right up next to the master. So what I thought was the "normal" play was the master engagement. I think this last adjustment has it pretty close to 100% dialed in, we'll see tomorrow.