1972 K2500 no rear brakes

[Fbks_Cruiser]

Hey guys. Been lurking here for a year or so since I got my truck. The forum is so useful that I can almost always find what info I need and rarely post. Thanks for all the great information. I got the truck about a year ago and have been repairing/performing much needed maintenance as time as money allows.

Sorry for the long winded post. I just want to give as much info as I can:

I recently discovered that the right rear brake wheel cylinder started leaking. So I replaced the brake hose between frame and rear axle, both left and right wheel cylinders, new shoes and hardware.

Next challenge was bleeding. I bled the heck out of the lines (by having a helper pump the pedal, open bleeder at the top of the pedal and close before pedal reaches bottom, making sure master never went dry) and kept getting air with the brake fluid. I ran 2 quarts of brake fluid through the system. Got frustrated and quit for the night. Today I got a couple of speed bleeders cuz I thought air was entering along the threads of the bleeders. Also used a mityvac and pulled a bunch more fluid and air through. Gave up on the mityvac and went back to the helper pumping the pedal with the speed bleeders in place. Finally got to where we got 15 pedal pumps through each side with no air.

But, now I still get no movement of the brake shoes when the pedal is pressed. Parking brake works fine and shoes are adjusted up to where they drag on the drums. Front brakes work fine. Dash "brake" light is on. Yes I did have the button on the front of the propotioning valve depressed using a zip tie.

Grrrrr. Took it out in the drive and tried stomping on the pedal but light didn't go out and still no rear brakes. I can't really pump up the pedal and have it keep firm. With pressure it creeps to the floor in a couple of seconds but I can't find any leaks?

Aside from the leaking wheel cylinder, the brakes worked fine before.

Suggestions?