The rear brakes do not work well

try adjusting the rear brakes first I am assuming they are drum brakes.

Yes Sir,
Everything is as it should be. It just appears that I get little or no fluid from the master cylinder to the rear brakes. But I do get fluid when I bleed them. Could there be a problem withe the master cylinder or could there be a problem with the proportioning valve?

sometimes rear brakes have to be readjusted after a few applications if you are getting fluid there is nothing wrong with master or pro valve. most of your braking is done on front so check adjustment once more.