No rear brakes??
 

After putting 72 disc on the front of my 70 I have no rear brakes. When I have someone pump the pedal I get just a very little fluid out the bleeder. It just ouzes out a little. The pedal does not go down when I open the bleeder.
I cracked the line at the rear of the Proportion valve and fluid ouzes out when the pedal is pushed. Could the proportion valve be bad and only a little fluid geting to the rear? It is an original 72 valve. The master cyl. and rear wheel cyl. are new. The fronts work fine.

Re: No rear brakes??
 

I just put a buddies used proportion valve on and it made no difference.

Is there any difference in the master cyl. for the Bendix booster and the delco booster? I have the Bendix on the truck that was on the power drum setup.

Re: No rear brakes??
 

I always gravity bleed rears with empty lines. Sounds like proportional valve did its job and closed. I've had to replace once that happens.
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Re: No rear brakes??
 

if you dont clamp the pin on proportioning valve like GM tells you to do in the service manual it leads to poor bleeding

also if the rod is not adjusted right for the master cyl it can cause little to no rear brakes

Re: No rear brakes??
 

Check the rubber line in the back on the rear end
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Re: No rear brakes??
 

Thanks guys. The pin seems to be all the way in which I assume closes off the rear. If I hit the pedal hard it jumps out and goes right back in. I just read in an repair manual here at work that to recenter the pin you should open a bleeder in the high pressure side and press the pedal and it would recenter.
I don't understand clamping it in. Seems like that would have it where it is now.

Re: No rear brakes??
 

I thought about the rear hose. But don't they usually colapse and hold pressure, as opposed to not letting the fluid flow towards the wheels.
And is there a way to measure for the push rod length as opposed to trying it at different lengths? I used it as it was before. I did check the original drum MC and the new MC and the old MC from the doner 72 and they all seem to be the same depth.

Re: No rear brakes??
 

if you dont understand clamping the pin that is exacly why GM went to the trouble of producing a factory service manual so people could understand the systems in GM produced vehicles// but if you dont read it well

Re: No rear brakes??
 

I've been working on vehicles for over 40 years and I'm alway open to learning something new. I don't have a GM manual can someone please explain the bleading procedure without being critical? Maybe with illustrations? A picture tells a thousand words. (I learned a lot from girly magazines too).

Without the GM book I'd try this. Open the front system and let it drain. It's only brake fluid. Blead the rear system first. This should by therory make the porportioning valve move the other way.

Re: No rear brakes??
 

65 on 24s was correct. The rear hose was on my list but I didn't believe it wouldn't let fluid through if standing on the pedal. I was wrong.