American Motors: Gremlin brake problem, differential valve, shoe return springs

Question
I have a 1972 Gremlin that I upgraded to front disc brakes and V-8 when I swapped out the front cross member from a 1974 with disc brakes. I changed out the master cylinder to one for front disc w/no power and rear drum. It all seemed fine until about 3 months of driving it and recently the front calipers were starting to bind seemed to be building up and holding pressure. I simply opened the bleed vavle and all was fine. When It did it a second time I replaced the calipers. Now it has once again done it with just one of my front disc brakes. Is there a reason that it is holding the pressure ? does the proporting/differential valve restrict flow or cause it to maintain pressure ? Just trying to figure out how to get the gremlins out of my gremlin !!  I appreciate the help. Thanks, Gordon

Answer
The disc brake set up should have a combination valve. It does three things:
1) Proportioning valve splits the pressures between the front & rear.
2) Pressure differential valve and switch activates the warning light in case of fluid loss.
3) Metering valve reduces front brake pressure until rear brake pressure builds up enough to overcome the brake shoe return springs.
Try replacing the combination valve. Make sure it is one for your donor vehicle with disc brakes. Also make sure your master cylinder is for disc brakes.