Brake Proportioning/Combination Valve: Description and Operation

The brake pressure control valve proportions the pressure to the rear brakes.
^ When the brake pedal is applied, brake fluid pressure passes through the proportioning valves to the rear brake system until the valve split point is reached.
^ Above its split point, the proportioning valve begins to reduce the hydraulic pressure to the rear brakes, creating a balanced braking condition between the front and rear brakes.