Proportioning valves regulate the brake pressure that goes to the front and rear brakes. Proportioning valves meter the fluid pressure that reaches the front and rear brakes to provide vehicle stability during braking. Proportioning valves are important on vehicles equipped with front disc brakes and rear drum brakes. Front brake pads are always in constant contact with the rotor, and rear brake shoes are retracted away from the drum when not in use. Proportioning valves keep the front brakes from applying before braking pressure reaches the rear brake shoes.
Brake Master Cylinder – An understanding of how a proportioning valve works begins with an understanding of how the proportioning valve is related to the master cylinder. Master cylinders have primary and secondary circuits that lead to the two brake lines attached to the master cylinder. When you press the brake pedal, equal fluid pressure is forced into the primary circuit and secondary circuits. The two brake lines lead into the proportioning valve, which meters the fluid pressure to the front and rear brakes according a ratio set by your car’s manufacturer.