71 Cuda pedal feel

[wantone]

Ok - Just installed a Cardone/A1 master cylinder and booster.   First 1/3 of the brake pedal press feels like only a suggestion -  Once I press hard, the pedal engages and it feels like only the front is stopping.   

I'll be rebuilding the rear drum pads and getting the drums resurfaced but... what would it be worth it to save the money and look into a disc kit for the rear brakes?   This would allow me to get rid of the potentially faulty proportioning valve right?

[73restomod]

Hmm master cylinders need to be bench bleed properly, failure to do so results in sponge city pedal you describe. Next, drum brakes need to be adjusted properly, this is done by opening up the star adjuster until you cannot get the drum over the pads. Back it off until they just slip over the pads, than back it off 1 more tooth, and your done. Then make sure to rebleed your brakes, starting at the farthest point from master and moving to the next closest wheel as you go. Get some clear tubing and a cup, break lose the bleeder screw have an assist press and hold the pedal, than close the bleeder screw and the assistant may release the pedal. Wash rinse repeat until you have no air bubbles in line.