Delco-Moraine Single Piston Rear Disc Brake

Fig. 1 Typical Delco-Moraine rear disc brake cross sectional view:

Fig. 2 Rear disc brake caliper exploded view. Eldorado, Firebird, Riviera, Seville, Toronado & 1982---86 Camaro:

Upon application of brake, Figs. 1 & 2, the cone and piston move out as one part. The nut remains stationary on the high lead screw and a gap develops between the cone and nut. When lining wear occurs, the cone and piston do not return to their original position, thereby leaving a small gap equal to the lining wear between the nut and cone. The adjusting spring causes the nut to rotate on the high lead screw to close the gap and adjust the caliper.
Upon application of parking brake, the lever rotation causes the high lead screw to turn and the nut to move down the screw, thereby loading through the cone and the cone-clutch interface of the piston, resulting in a clamp load on the linings. When the parking brake is released, the cone rotates on the clutch interface to adjust the caliper. The clutch interface prevents the cone from turning when the parking brake is applied.