US Patent 7343741 Vehicle master cylinder

A master cylinder (1) having a bore (3) fitted with at least one piston (4, 5) and at least one seal (19, 20, 21, 22). The seal (19, 20, 21, 22) is partially stiffened by a reinforcement member (25). In order to retain the piston (4,5) in the bore (3) a groove (31) is located on a circumference of the piston (4,5) against which the sealing member (25) bears with the piston (4,5) in a rest position to retain the piston (4,5) in bore (3).