I need some advice
I have a 1976 F250 4x4 and am having some brake issues....

Last week, I had the brake pedal go to the floor once or twice, no visible leaks, so I changed the master cylinder.
I bench bled the new Master Cylinder, upon install, brakes weren't great, so I decided to bleed the brakes using a vacuum type bleeder, I got no fluid from the rear brakes.
I then removed the proportioning valve, checked it over, and it seemed to be in a position where it routed the fluid to the front discs.
I reset the valve and then re installed proportioning valve and am still no able to get any brake fluid from the rear brakes. I even tried the front discs and bleeding happens no problem.
I am probably gonna re and re the proportioning valve to triple check things.

Any suggestions??
Thanx
Darren

 

I see no one has responded to you yet, so I'll jump in. Hopefully someothers will have additional thoughts.

I don't think the stock proportioning valves are adjustable. And you should be able to adjust an aftermarket valve without removing it. Stock will have the brake warning light wires attached, aftermarket wont. If you remove the rear brake line from the valve and pump the brake, does fluid come out? If not, you just may need a new valve.

 

Are you sure your lines from the pro valve to the rear wheel cylinders are good and NOT clogged? I would replace the rear wheel cylinders sice tyou are that deep into it.

Remember to put a ton of anti-seize on the bleeder plug threads, NO in the end.

Did you do a regular brake bleed (non vacuum type) after the master cyl change? Is there any fluid in the power brake booster vacuum lin?

That piston in the provalve should float in there and only move when it registers a large fluid loss, meaning you have a major line leak or blew a wheel brake cylinder.

Does out proportional valve have a small pin sticking out of it? Some manuals say to push it in or hold it out during brake bleeding.....

 

Time to disconnect it at the top of hose down to the rear axle and see if you get fluid there. If so time to check or replace that hose.