I am having a problem bleeding the rear brakes on an '84. I have just installed new brake lines and rebuilt the calipers, so the brake lines are empty. The front brakes bleed fine but I cannot get any fluid flow to the rear brakes. In fact you can just open the front bleeders and the fluid will flow out without applying any pressure. I am using the open bleeder-depress pedal-close bleeder- release pedal method and when you depress the brake pedal, there are a few bubbles expelled from the rear caliper, but when you re-open the bleeder to start another stroke, the line has a vacuum on it and sucks fluid back into the bleed hose. I tried waiting for at least a minute, but the vacuum is still present.

I also tried to vacuum bleed the rear lines by applying suction to the rear bleeders, but that did not draw any fluid from the master cylinder.

After many attempts to bleed the lines, I removed the master cylinder tried to bench test it. With the MC held in a vice, I can push the cylinder in and get the front brake reservoir to draw fluid, but not the rear reservoir. I completely disassembled the MC and everything looks nice and clean, no cylinder scoring, all seals look like new. Is there any trick or special procedure in getting the rear brake line filled?

I purchased a NAPA rebuild kit (my local Chevy place says that GM no longer sells the kit), but it did not have a new proportioning valve, just the rubber seals. Haven’t installed the kit yet since I don’t really think that the seals are the problem. Any suggestions as to what might be causing this problem.
Thanks,
Charles

 

Try these steps...has to be the MC

 

Thanks. Anyone have any idea what the "special grease" used the combination valve might be?

 

If there is vacuum on the bleeder when you open it, you are not bleeding properly. There must be pressure when you open the valve, positive pedal pressure.

Two other points:

1.) Don't let the pedal go to the floor, place a hunk of wood or something to prevent full travel. This prevents damage to the seals on the MC.

2.) Use a length of clear , tight fitting hose from the bleed vavle to a container of new brake fluid. This prevents the mistake of drawing in air if the pedal is released before the bleeder valve is turned off.

Now that the MC is back in, crack each line only with pressure on it, just like above. If one cannot eventually push a little fluid out after the air, you my man now have a bad MC. Replace and start over. Don't allow the ABS to cycle, and this includes the "test" it does when you first start and run to 4 mph or whatever.