Hydraulic wheel cylinder assemblies and drum brakes incorporating same

An internal shoe drum brake comprising a pair of brake shoes, a hydraulic wheel cylinder assembly interposed between one pair of adjacent ends of the shoes and a mechanical expander and fixed abutment means interposed between the other pair of adjacent ends of the shoes, the hydraulic wheel cylinder assembly comprising:

• a cylinder body having a through bore therein;
• a pair of piston assemblies slidable in said bore;
• an inlet port in the cylinder body which opens into said bore for supplying hydraulic pressure to urge the piston assemblies away from each other;
• an automatically adjustable variable length tappet assembly incorporated in each piston assembly, each tappet assembly comprising a rotatable screw-threaded component interengaged with a non-rotatable screw-threaded component;
• a one-way drive mechanism associated with each tappet assembly and comprising a driven member which is rotationally fast with the rotatable screw-threaded component and a driving member which is rotationally fast with the cylinder body;
• a spring connection between the driven member and the rotatable screw-threaded component allowing relative axial movement therewith;
• and stop means on the driven member for limiting movement of the driven member in the direction of the other piston assembly, the arrangement being such that the spring connection yields during continuing movement of the screw-threaded components in the direction of the other piston assembly when the driven member is arrested by said stop means.