Abstract: A hydraulic disc brake for a vehicle comprising a rotatable disc adapted to be coupled to a wheel for rotation therewith and a frame having a pair of cylinders in which are located pistons for moving brake shoes toward the disc for engagement therewith when fluid is admitted to the cylinders. A flexible cup is slidably located in each cylinder between its piston and its rear end for forming a movable seal between the cup and the wall of the cylinder. The cup comprises a forward wall having an annular side wall extending rearward therefrom; a central hub spaced inward from the annular side wall; and a plurality of angularly spaced webs extending radially between the central hub and the annular side wall.