In motor vehicles a brake assembly is usually provided at each ground wheel. Sometimes disc brakes are provided on these wheels.
A conventional disc brake assembly comprises a circular disc connected to the road wheel, and a disc brake caliper mechanism encircling an edge area of the disc at or near the twelve o'clock position. A piston contained within a cylinder bore acts within the caliper mechanism on disc brake pads arranged along opposite faces of the rotating disc to exert a clamping force thereon when the motorist applies foot pressure to the brake pedal.
After a period of service the brake pads become worn, thereby necessitating their removal and replacement with new brake pads. One problem encountered during the brake pad replacement operation is retraction of the associated piston into the its cylinder bore. During service the disc brake pads become worn and thus thinner. When it becomes necessary to replace the pads because they have become too thin for effective operation, the brake cylinder piston is in an extended position projecting a significant distance out of the associated disc brake cylinder bore. Before new pads can be inserted into the caliper mechanism it is necessary to forcibly retract the piston back into the cylinder bore (because the new pads are appreciably thicker than the worn pads, and therefore take up more axial space in the caliper mechanism). Retraction of the disc brake piston into the cylinder is made difficult because the brake fluid in the piston is in a semi-pressurized condition. Also, the piston seals offer some resistance to disc brake piston motion into the disc brake cylinder bore. Occasionally, the disc brake piston-cylinder bore interface becomes corroded or packed with contaminants or sludge, thus posing another obstruction to retracting motion of the piston.
Conventionally, the changing of brake pads on a disc brake caliper assembly was accomplished through the use of a C-clamp or some device operating similarly to a C-clamp. Mechanics found the use of such a C-clamp to be somewhat difficult because of the lack of control associated with it. Such a clamp tends to wander from the center of the piston and could cause damage to the cylinder bore if excessive pressure is applied. Thus, the continual wandering or walking of the C-clamp or other device while trying to depress the piston into the cylinder bore required many resettings to perform the otherwise simple operation of depressing the piston into its retracted position within the piston cylinder bore. Much time and potential damage is associated with the present state of the art. Thus, there is a need for an easy to use, inexpensive, lightweight, compact, easily transportable disc brake piston retraction tool.