F 150 2WD Pickup V8-4.6L SOHC VIN W (1998)
Brake Proportioning/Combination Valve: Description and Operation
The brake master cylinder fluid control valve regulates the hydraulic pressure in the rear hydraulic circuit. It is located on the brake master cylinder and
is screwed into the rearmost outlet port. When the brake pedal is applied, the full brake pressure passes through the brake master cylinder fluid control
valve to the rear hydraulic circuit until the valve's split point is reached. Above its split point, the brake master cylinder fluid 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 lockup
during hard braking.
In case of 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.