Brake Proportioning/Combination Valve: Description and Operation

Proportioning Valve:

PURPOSE
A proportioning valve, where used, is integral to the master cylinder. It proportions pressure to the rear system.

OPERATION
The brake pressure control valve regulates the hydraulic pressure in the rear brake system. It is located between the rear brake system's inlet and outlet ports in the main valve. When the brake pedal (2455) is applied, the full brake fluid pressure passes through the brake pressure control valve to the rear brake system until the valve's split point is reached. Above its split point, the brake pressure control valve begins to reduce the hydraulic pressure to the rear brakes, creating a balanced braking condition between the front and rear wheels to minimize rear wheel lock-up during hard braking.

In case of the front brake system malfunction, the brake master cylinder fluid control valve has a bypass feature, which allows full hydraulic pressure to the rear brake system.