Patent ID: 7530227

Claim:
A brake apply master cylinder comprising: a) a brake-apply-master-cylinder body including a bore, wherein the bore has a longitudinal axis, a closed front end, a primary fluid outlet fluidly connectable to a primary brake circuit, and a secondary fluid outlet fluidly connectable to a secondary brake circuit; b) a piston assembly including a single brake apply piston disposed in the bore; wherein the piston assembly fluidly divides the bore into a primary fluid chamber in fluid communication with the primary fluid outlet and a secondary fluid chamber in fluid communication with the secondary fluid outlet, wherein the primary fluid chamber has a first chamber volume and the secondary fluid chamber has a second chamber volume, and wherein longitudinal forward movement of the single brake apply piston reduces the first and second chamber volumes; and c) a return spring assembly disposed in the bore and extending from the closed front end to a return-spring seat of the single brake apply piston; wherein the return spring assembly includes a front spring stop member contacting the closed front end, a rear spring stop member contacting the return-spring seat, and a coil spring having a first end contacting the rear spring stop member and a second end contacting the front spring stop member, and wherein the return spring assembly includes a hollow pin extending between and limiting outward longitudinal movement of the front and rear spring stop members, and further wherein the front and rear spring stop members each include an annularly cylindrical wall having at least one through hole.