On some model vehicles, a Metering Valve may be installed to balance the pressure between the front disc brakes and rear drum brakes on vehicles with front disc brakes. On some model vehicles, a Proportioning Valve may be used to reduce the hydraulic force applied to rear drum brakes during rapid braking, preventing rear wheel locking and skidding. A Warning Sensor turns the brake warning light on during a hydraulic brake malfunction. If not working, this switch should be serviced or replaced. Damaged lines should be replaced.
Cracks can form from temperature variations and aging.
Inner surfaces can become clogged. Leaks can occur at end fittings. New hoses should be installed for any of these reasons. The frictional contact of the Brake Shoes slows and then stops the drum. As brake shoes wear down from normal usage, cylinder pistons are spaced out farther than usual in the chamber.