72 brake issues

[72chevylwbmo]

Now to the next problem. Brakes. I put all new brakes, bearings and seals up front. Went to work on the rear and there isn't any brakes back there. Tried to bleed them and I don't get anything but a drip out of the bleeder screw. You know how when you bleed the brakes and you pump them up, hold, crack open the screw that the pedal goes to the floor. Mine doesn't. So my question is, is it just bad wheel cylinders or could it be the proportioning valve is bad? I have also put on a new master cylinder and booster.