Single-piston Wheel-cylinder Shoe-expander.
Single-piston wheel-cylinder units are normally used on front drum-brakes, to provide higher braking efficiency. Two single-piston units are fitted diametrically opposite each other. The single-piston unit expands one shoe against the drum and acts as the anchor abutment for the other shoe, thus performs the dual functions. If the outward movement of both the single-piston units is in the direction of forward rotation of the drum, the combination is known as a two-leading-shoe brake (Fig. 28.41). single piston wheel cylinder Similar to the double-piston units, the single-piston units are bolted to the back-plate. These units work in similar way to that of the double-piston ones, except that the cylinder has a blind end to form the anchor abutment for the other shoe. Either the ring-seal or the cup seal with a seal-spreader and retainer-spring is used to seal the piston.