Piston anti-knock back assemblies

In a disc brake assembly having a brake actuator comprising a piston slidably mounted within a cylinder bore having a side wall and an end wall, said actuator being operable to urge a friction surface into contact with a rotary disc surface upon supply of hydraulic fluid under pressure to said cylinder bore, said cylinder bore having an enlarged stepped section therein adjacent the end wall of the cylinder bore, a piston anti-knock back assembly comprising:

• said piston having a conical frustum formed head facing the cylinder bore end wall and an annular groove adjacent said head;
• an expanded resilient split ring in frictional contact with a main portion of the cylinder bore side wall, and loosely axially located in said annular groove by expanding said ring over said conical frustum piston head until said ring snaps into position in said annular groove;
• said ring, when unexpanded, being a sliding fit within the main portion of the cylinder bore and having abutment spacer means on one side of the ring which, when the unexpanded ring is inserted in the cylinder bore as far as said stepped section of the bore, contacts said cylinder end wall and maintains the plane of the ring far enough from the cylinder end wall to allow said conical frustum piston head to be thrust through the ring to locate the ring in position in said annular groove, said ring frictional contact with the main portion of the cylinder side wall acting so that said ring may be movable by said piston during piston actuated movement but not during piston retractive movement.