I have a 69 cutlass I have put rear disc brakes on and cannot get any pedal on car, let me re say that, You can get a good pedal from pumping the brakes, leave it alone a minute and goes away, But can be pumped up, It was a kit, have also replaced the master cyl and prop valve twice, have stainless hoses, from what I can tell is the brackets on the rear must be a little off to where pushing the caliper pistons back too far, I have tried dragging the parking brakes on the lift to try to seat the rear pads in to no avail, have completely blocked rear brakes and have a great pedal, Any one ever run across this situation?

 

What does the manufacturer say that you bought the kit from? They must have run into this before

 

Did you use a residual pressure valve to maintain some fluid in the calipers when the pedal is released?