I have a 71 chevelle I converted the front power drum brakes over to power disc brakes..seems now that the rear brakes are the only ones working..I put a used prop valve on the car ..maybe my problem?..how can I test it..?..or maybe the power booster isn't working is there a test for it?Do they make a repro for it?I used all new parts except for the prop valve and the shorter rod that goes from the master cylinder to inside the booster..I did bleed the lines..When I took of the wheels..the rotors looks good but there was a rust film on them like the brakes hasn't been working.

Sounds like air in the lines. I did the disc swap on my 68 and had the same problem. Try bleeding the fronts again and make sure the the bleeder screw is pointed straight up (so all the air is at the top of the resevoir, you might have to take the calipers off and position them so the bleeder screw is stright up!) this fixed my problem instantly.

could the pushrod be adjusted too long
this would cause the master cylinder to not be able to refill with fluid from the reservoir

How is the pushrod adjusted?

Originally posted by Tom's 68 conv:
could the pushrod be adjusted too long
this would cause the master cylinder to not be able to refill with fluid from the reservoir

Anyone?anyway to test the booster?

right off the pedal the rod that pushes the power booster should have a 3/8" threaded rod with a jamnut right at the u clasp that mounts to pedal (the other style has an eye either way they both should be adjustable)
unhook the u piece and see if at rest it is at the pedal hole or if it wants to push beyond that hole
if it pushes past the hole shorten it until it is just a tiny bit shorter than the hole (about two turns shorter than when it is even with hole when pedal is pulled all the way up to rubber stop)
also some systems will have an adjustable pin between the mc and power booster (if this was taken off another car and put directly on this car without changing the booster or mc chances are good that the pin is NOT the problem)

noticed you changed from power drum to power disc
did you use original booster or the booster that was used with the disc system
I read the original post and realized the power drum part

I used the original power drum booster..can this be the problem..??


Originally posted by Tom's 68 conv:
noticed you changed from power drum to power disc
did you use original booster or the booster that was used with the disc system
I read the original post and realized the power drum part