I put a rebuild kit in my master cyl last summer in hopes of fixing a leak. Still leaked but worked fine. I recently had it sleeved, reassembled it, and put it back on. No leaks now. BUT something isn't right. After bleeding twice with the front delay valve plunger depressed (I've done this many times on this car so I know the procedure), it just doesn't seem to have the pressure it once had. Pedal is solid but doesn't want to stop the car without a lot of pedal pressure. Also when you push on the pedal hard the brake warning light comes on. I sent the MC (assembled) back to the place that sleeved it, and they said it checks out fine with over 800 psi output front and rear. No other changes were made to the brake system and the power booster was rebuilt 3 years ago. It's a '69 with stock power front disc, rear drum.

It sounds to me you still have some air in the lines. Did you bench bleed the master before installing? Even if you did, I would bleed it again on the car. Then I would bleed the brakes one more time, but in reverse order of the way you did it last time. I say that because once I had a softer pedal than usual on my vette after bleeding. I always start from the rear brake farthest from the master and work back to the closet wheel to the master. But just out of frustration in not getting a hard enough pedal, I bled them starting at the closest wheel to the master and worked out to the pass side rear. It worked wonders. The pedal came back as hard as it always was and has worked great since. Maybe worth at try.

Yes I bench bled the MC. The pedal was good and solid. The first time of the two bleedings I started closest and went to furthest. The second time I reversed that. I've installed MC's on this car twice before with no problems. When I get it back I'll try it one more time before saying the hell with this and buying a new, incorrect appearing one.

I wonder if one of the spring cups inside the MC isnt leaking, it would probably be the secondary because if it were the primary, you'd have fluid coming out the back of the master cylinder. If the secondary cup was leaking, the secondary piston would be pushed by mechanical pressure from the primary spring, not hydraulic pressure like normal - this could cause your hard pedal.

Thats all I can think of Von, i'm sure you've thought of everything else.

The brake warning light is triggered by a pressure differential switch in the distribution block/prop valve. A malfunctioning MC can cause this light to turn on.

I wouldnt rule out the booster either, if you had fluid leaking from your MC, like you did in the past, the fluid can deteriorate the diaphragm in the booster. Have you checked the one-way vacuum valve?

Dont know if any of this will help you.

-Adam

Any updates Von?

I finally fixed it. The problem was air still in the rear lines. With the car jacked up, the fronts worked fine but you could turn the rear wheels by hand with the brakes applied. The pedal was solid though. I had always used a regular straight open end 5/16" wrench to bleed the rears with no problem except I had to hold the wrench at an angle to be able to turn it. I was using a smaller hose this time too and I guess holding the wrench at an angle was causing air to get back into the line. I bought an offset box end bleeder wrench yesterday and tried it again (about the 4th time). Voila! Rear brakes work and no more warning light. I really felt stupid. graemlins/clonk.gif