Abstract: An improved seal is disclosed for hydraulically sealing a piston-cylinder assembly used in activation of a floating caliper disc brake. The improved seal comprises an annular groove circumscribing the cylinder wall within which a ring type elastomeric seal is seated so as to sealingly engage the piston. The floor of the annular groove has a flat portion and sloped portion. By varying the ratio of the flat portion to the sloped portion a desired axial force resisting retraction of the piston into the cylinder may be pre-determined thereby preventing excessive brake shoe drag upon the rotor.