When I bought this 80 model RX7, the brakes were terrible, it had been sitting for a few years. So I replaced the master cylinder, new rotors and pads. The calipers are working fine as the front brakes will stop the car. The problem is I have bled the back brakes until clean fluid is coming out with no bubbles, but they will not pump up at all. When I have someone push down on the pedal and hold it, very little fluid comes out with very little pressure. With the drums off, the shoes dont move at all. I have no leaks anywhere. Could the proportion valve be bad and not sending pressure to the back brakes? When I bench bled the mc, the port for the rear didnt seem to push fluid as fast as the port for the front.

 

I now have the rear brakes working. It was the proportioning valve.

 

Nice one on finding that one by yourself!
Anyway, on those situations it could be a clogged tube somewhere in the path to the rear brakes, brakes poorly bled, or the proportioning valve as it was in this case.

Cheers!

 

Good...glad you got them to work