Rear brake lockin up HELLLLLPPPPP!!!

[78cut]

I have a 78 cutlass supreme and last week I noticed that my front brakes seemed to be fadin away. About 4 months ago I replaced the master cylinder and the two front calipers and it was cool until last week. I thought maybe it was the brake booster so I went to pick and pul and grabbed a booster and master cylinder from a 84 Cutlass. The car still stops but when I apply hard pressure to the pedal at about 35 mph the rear locks up bad. The pedal is hella mushy. I ran about a bottle of brake fluid through the front calipers and there were still bubbles comin out of the front right wheel. The driver's side was fine. I assume there is still air in the line but sh*t man how much fluid do I need to run through it. I didnt bench bleed the master cylinder could that cause the lockup and mushy pedal? Also there is no loss of fluid so I doubt there is a leak anywhere. Bad combo valve?

 

[1980Gbody]

i would bench bleed the master cause u have to do that with a new one if that dont work check the rear wheel cylinders but that wouldnt cause bubbles in the front

 

[pontiacgp]

if you don't bench bleed the master you'll never get the brakes working right.....and check the proportional valve ..there is a button on the valve to reset it and if that doesn't work I found backing to car up and slaming on the brakes reset mine... and when your bleeding the brake lines make sure you start from the wheel furthest from the master