1978 Toyota Pickup. Its got a brake issue, all brake power is being applied to the front brakes. Replaced booster, proportioning valve, and master cylinder.
Did you get the rear brakes blead out all the way?
Sounds like the proportioning valve is stuck. What this valve does is close either the front brake lines or rear brake lines from fluid flow. The plunger inside moves to which side appears to have a leak effectively stopping the leak so you still have some brake. To fix this you need two people. You will have to have one person pump up the brake pedal and bleed one of your front calipers. If the valve is still working properly this should move the plunger back into place and your brakes should work properly. If not you might have to replace the valve and bleed it again. Good luck.
Recheck the brake lines to the rear. that old of a rig they could be full of crud or collapsed internally, pay close attention to the rubber hoses.
Mine on my 78 turnd out to be the rubber flex line on the rear end. I started cracking open every fitting from the master to the rear cylinders. when i stopped getting brake fluid i had found it. i replaced it with another one i had; problem solved. Brakes work great!
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