brakes

[PromiseKeeper]

had a leaky master cylinder..... 1980 c-10 2wd. Installed a new one. Bench bled it before installation. When trying to bleed the rear wheel cylinders, getting next to no fluid to come out. Fronts bleed like they should. I can take the bleeders completely out and still just get a few drops. Any ideas on what it could be?

[Captkaos]

Were the lines in the rear empty before?  If so it takes it a while to get them full.

[PromiseKeeper]

not sure thats the problem. Had a helper keeping pressure on the pedal and it wasn't going down either. Could it be the proportioning valve? Can this get out of sync somehow? If so, can it be reset? Cant figure what happened. Before I started this, everything was working, just had a leak at the master cylinder

[zieg85]

Sounds like the proportioning valve is doing its job.  I have had luck about 50% by bleeding the front a bunch and hard.  Makes a mess but you have to move fluid fast and it may switch back to the center.  I have also gotten lucky by tapping on the valve while bleeding the front.

[bake74]

     I have had luck with what zieg stated, also I would diconnect the rear lines and blow them out with air just to make sure something did not plug them up.

[PromiseKeeper]

Does the rubber hose at the differential cause problems like the front ones do? I'm thinking it has to be either that valve or something ahead of the rear lines since they both do the same thing

[zieg85]

Does the rubber hose at the differential cause problems like the front ones do? I'm thinking it has to be either that valve or something ahead of the rear lines since they both do the same thing

Yes it can but "usually" the problem, at least when I have had a bad hose in the rear is that the rear brakes are slow to activate and slow to return causing the brakes to drag for a bit.

[PromiseKeeper]

This thing is driving me crazy (I know...short trip!  ) Tracing this thing backwards until I get to the master cylinder. Cracked the fitting there and the front one had fluid coming out like it should. Back one had a couple of drips. Called the parts guy and he says bring it back...you probably got a bad one. Did that and 2nd one did the same thing! Now he's saying maybe we have the wrong part number?? Shouldnt both chambers put fluid out where the lines hook in? Yes, I did bench bleed both of them before installation. But as I see it, there is no way I can get the back to bleed if the master cylinder isnt putting the fluid in the lines. I'm thinking Chris needs to add a therapy forum for these kinds of things 

Also, I did look at the proportioning valve and the pin is not sticking out.

[thirsty]

If it were mine I would take a line off one of the rear wheel cylinders and put a mighty-vac on the line to see if you have good flow to that point. Before you do that check that your bleeder screws are not plugged up.