Abstract: Actuating piston of disk brake is provided with self-retracting 3-element control unit carried, typically, in surrounding annular piston recess with one element in frictional or tensioned registration with wall of piston chamber. Elements are (a) radially tensioned anchorage ring which frictionally abuts chamber wall at piston-extension position, (b) axially compressible/resilient co-axial ring such as elastomeric O-ring, compression spring, or corrugated metallic washer which is compressed by piston extension, (c) positioning and limit bracket which locates a and b and provides axial channel for reciprocation of piston in response to fluid pressure from brake pedal. Upon relief of fluid pressure, expansion of compressed co-axial ring b "lifts" piston to retracted position. Unit may be installed as original equipment on vehicles, etc. or existing piston assemblies may be modified to incorporate such.