Have no rear brakes on my 68 Cuda drag car. Car has 4 wheel drums. Changed master cylinder and bled brakes, still no rear brakes. Getting fluid to the wheel cylinders but not near as strong as the fronts. The rear cylinders dont even move. It has the stock proportioning valve. Could this valve be stuck?

proportioning valve or basic T splitter? With a 3/8" line wrench I'd take off the rear hard line at the back side of the PV & see if you have PSI. If so that only leaves a collapsed rear flex hose (way less likely)

If the distribution block on the frame rail is still the original one it is nothing more than a distribution block, no proportioning is done thru it.

How old is the rear hose from the body to the rear axle ? Do you have the correct master cylinder ? Front brakes do most of the stopping so they naturally have more bias built into the master cylinder.

Dont know for sure if its what came on the car but it does have a switch on it for a warning light. All the lines from the valve back look to be almost new with no crimps etc. The car was raced up to the week I bought it. I have hadit for about a year building motor, trans etc.

The original original block will also have a switch for the light , they look similar. Crack open a bleeder on a front wheel and put a line on it into a container and hit the brake pedal fairly hard , if the valave is stuck toward the rear causing a restriction, this might cause it to pop back ?

Sounds like you haven't eeven driven it , what is leading you to believe there are no rear brakes ?

another way to rule out the distribution block is to remove it from the system , a tee for the front lines and a coupler for the rear , the block is mainly to turn on the idiot light if one part of the system fails .

Yes I've driven it . Low gear bursts in the road in front of the house. Stopped alright then. Took the car to the strip on test and tune night. Did a half pass to make sure everything was working. Used every inch of the shutdown getting stopped. A&&hole is still puckerd!!! Believe me I got no back brakes!

Hopefully discs in the future, at least fronts. But need to get the drums right for the time being. I'll take the line coming out of the block running to the rear brakes loose and see what I've got. If not much pressure there, I'll do away with the block and run the lines as suggested. Also the hose at the rear looks to be almost new as is all of the hard lines coming from the box. Thanks to all that offered help.