No fluid coming out of master cylinder to the rear brakes

1971 Buick Skylark Custom 350/2 barrel, 4 door with factory front disk brakes.

I bought new:
Master Cylinder, Centric 130.62001 (new, premium, for front disks)
Power brake booster A1 Cardone 5471106 (remanufactured)
Combination/Proportioning valve with bleeding tool
Disks, pads, and hoses up front
Wheel cylinders, drums, shoes, springs, and hose in the rear.

This has been a week long process trying to diagnose but I think we are finally narrowing it down and would like some guidence. When we bench bleed the master cylinder we get fluid out of the front and rear ports. However when its on the car, 99% of the time we don't get any fluid out the rear port on the master cylinder. I mean, port wide open, no line attached to it, pumping the brakes, and nothing comes out. The brake pedal has full travel. I'm thinking it has to be related to the pushrod in the brake booster or something being out of adjustment. Any ideas? As far as I can tell the push rod on my booster isn't adjustable. Wrong part perhaps? I'll be working on it today and try to get some measurements.

 

I'm afraid I don't have the old MC anymore. It was leaking on the garage floor so I tossed it. I do still have the old booster though. From what I noticed bench bleeding, fluid seemed to be coming out of the rear port as soon as the piston was depressed.

 

I bought another master cylinder at auto zone today to test it, a new Duralast model number NM1521. I bench bleed it and put it on. I opened the rear bleeder ports and pumped the brakes for several minutes and not a single drop of fluid came out the rear. Thinking there may be a blockage I disconnected the rear hard line where it goes into the rubber section and blew air through it. It sprayed air out of the bleeder ports. Then I disconnected the rear hardline coming out of the combination valve and blew air through there and it sprayed a bunch of fluid out of the rear where it was still disconnected. Then I blew air up through the combination valve (with the master cylinder removed) and it sprayed fluid all over the engine bay. So all of the lines are clear, no blockages. I put the new master cylinder back on but left the rear line coming out of the combination valve and had my wife pump the brakes several time and no air or fluid came out. Then I removed the rear line going into the combination valve and had her pump some more and got a few drops and sputters. I'm at a loss and getting pretty frustrated.

 

If he is "Pumping " the pedal like he says with the line disconnected he is sucking air back into the master. Larry is right. Bench bleed completely then gravity bleed at every connection. Plus is he going by the instructions with MC that tell you that you can put plugs in the MC outlets and bleed it that way ?? You need to attach a line and direct it back into the master fluid to be sure there are NO bubbles.

 

Yeah Jason . not enough info. The last couple of MC I've seen provide instruction about using tubes to direct fluid from the outlet back to the reservoir . Or a alternate is to use plugs in the outlet and bench bleed it that way ?????? Thats stupid.

 

I have a bunch of metal lines with different fittings bent to reach the reservoir . I just watch the end of the line while its in the fluid

 

Anyone ever have the hold down valve not unload after bleeding the rears? I did and could not get it to release no matter what I tried. Even pushing/pounding hard
on the brake pedal. Purchased new prop valve.

 

Is the rod from the booster the correct length? May not be getting enough travel I've seen that before when changing out masters.