Brake Systems - Hydraulic System Control Valves: Description
All vehicles have some type of hydraulic system control valve or warning switch within the brake hydraulic system. Unit is usually mounted on frame or firewall adjacent to master cylinder. The front and rear brake lines are routed through this valve to their respective caliper or wheel cylinder. Vehicles with drum brakes only use a pressure differential brake warning switch only. Vehicles equipped with disc brakes use a combination pressure differential warning switch with a proportioning valve, or a metering valve, or both.