HELP NO REAR BRAKES

[kcandc]

I have converted my 68 over to power front disc brakes. I used the single piston calipers, a 11" Booster, 1968 Disc/Drum master cyl with the new style combo/porportion valve. Bled all the air out, (pushing in on the front button on the por. valve) and I have no rear brakes. The front rotors stop when you push on the brakes, but the rear's do nothing. Removed the drum and no movement at all. The wheel cyls are new too. Fluid came out while bleeding, but real slow. WHAT IS WRONG? Should I put a later model Master Cyl on???
Any help would be appreciated, Thanks Karl

[JohnZ]

Did you replace the rear flex line from the body to the axle? When they get old, they deteriorate and swell up internally, limiting or blocking fluid flow.

[kcandc]

Thanks for the input, will replace it as it is the original, Karl