brown7373

I just replaced my power drums with power disks, using all factory components, rebuilt calipers, new hoses, new master cylinder etc.


I made a tool to depress the switch on the distribution block. I gravity bled the left front, then right front with no problems. But I get nothing from the rears. When gravity did nothing, I got someone to push the brake while I opened and closed the bleeder valve. Nothing. I tried with the clamp on and off the distribution block.


I noticed that the piston on the distribution block is pushed in but doesn't come back out. I removed the rubber cup and it seems to be pushed in. Is my distribution block defective? I tried to pop it out by pumping the brakes with all the bleeders closed. The pedal goes to the floor but no fluid and the pin won't pop out.


Any ideas?

rcrac3r

You could try giving it a couple of light taps with a hammer. I've seen that back in the day once in awhile. When you replaced the master cylinder did you get all of the air out of it on the bench before connecting it to the brake lines? If not that might be part of the problem as well.

brown7373

I bench bled the MC, and have tapped on the distribution block, but so far no change. I've done brakes dozens of times, probably a lot more, and never had this problem before.


If the button is stuck in, would that stop the flow to the rear wheel cylinders?

rjohnson442

I could be wrong and i'm sure an Eric or Joe will correct me but I think you have to change the distribution block as well. there is a different one for discs/drums then drum/drums.

brown7373

I did change it. I have been calling it the distribution valve, when I should have been calling it the combination valve as shown in Figure 5-8 in the 1972 Service Manual.


Should the pin pop out on it's own, or is there something I can do to force it out?

brown7373

I just remembered that in a 1969 Corvette I had some time back, there was some kind of proportioning valve or combination valve that if it got stuck, you opened one of the bleeders and applied the brake, and that would force the valve to center itself. Does that apply here?

redoldsman

You have to change the distribution block to a proportioning valve. Brakes on A bodies are a pain in the butt. They are hard as heck to bleed. I purchased a reverse pressure bleeder and used it on my 54. I still need to do brakes on my 72 Cutlass convertible. I bought the pressure bleeder on ebay and it was cheap. Here is a link to one.

http://www.ebay.com/itm/Brake-Clutch...6c5d4f&vxp=mtr

Hope this helps

joe_padavano

The problem is that the internal piston in the combo valve (item B in the drawing) can get pushed all the way to one end of it's travel if you are bleeding the brakes and there's air in the other side. If the combo valve is used (especially if it's an OEM cast iron version), rust in the bore can cause the piston to stick.

Try closing the back bleeders and opening one of the front bleeders a little. Now press hard on the brake pedal. This will often move the piston towards the front (though moving it too far can simply cause it to stick the other way).

If this doesn't fix it, completely unscrew one of the back bleeder screws and see if anything comes out. I recently had a situation on a friend's Supreme where we couldn't bleed the back brakes. It turns out that there was rust in the wheel cylinders, blocking the bleeder port. I used a piece of copper wire to poke in the bleeder hole to loosen the rust, which finally allowed fluid to flow, but naturally this usually means it's time for wheel cylinders.

brown7373

I replaced everything, front & rear on the power brake system 8 years ago (how time flies). The rear shoes did not need replacement and the brake system was functioning fine, other than some pulling to one side or the other. Normal braking was fine, but needing a quick stop usually meant it pulled one way or the other. I could never solve that. I DID change the distribution valve to the factory combination valve, and I did that at the outset. It had been closed up tight, with short brake line pieces attached and then ends sealed off, and it appeared to be in good condition. I will try to pop it loose, and also removing the rear bleeder valve. I may then try new wheel cylinders if it still won't bleed.

costpenn

When I did finished the resto on my 72 drum brake vert last year, one of the last things to do was the bleeding. I replaced EVERYTHING on it with new items except for the reman/replated booster. I still don't know why, but it took at least 30 minutes at each rear wheel of the old two person pump/open & close deal to finally get them bled. I had bench bled the MC.

brown7373

Maybe I just need to bleed it to death. I assumed that since my rear lines were full of fluid, it wouldn't take much to get it flowing out back. The front flowed using gravity in very short order. But when I switched to the rear, nothing. The manual isn't explicit, but I read it to mean you keep the combination valve button pushed for both front and rear. Is that correct?