You sure you have the right master? The piston changes between the years for power/manual operation. Maybe you have the 7/8" piston and you need the 1 1/8". I stole the disc's off of a 75 A-body along with the prop block and suspension. I loved my manual disc brakes. One less thing in the engine bay of a 70 Dart. Slant 6. Also make sure your brake lines don't have a bubble where the banjo is, might have fluid escaping or sucking air in with every pump. I use the stainless braid on brake lines.