Help!!! Bleeding brakes

[lucifer]

Need some help and this forum is the place to get it.

I have installed 4 wheel disc on my 64 with new master cylinder and proper proportioning valve from CPP. I have properly bench bled the master and gravity bled the calipers,,,then power bled the calipers...then did it all again and I can't seem to get any pedal. Brake rod is correct and so in the master to booster rod. Proper stroke with about 1/4 inch clearance on the pedal to booster. All components are new and properly matched. I can get a partial pedal with three pumps and it will hold. Just can't get a hard pedal!
This should be so simple and I have done it more times than I care to admit.
WHAT AM I MISSING?????????????

Luc