Brake Proportioning/Combination Valve: Description and Operation

EXCEPT AEROSTAR, BRONCO II & 1983---87 RANGER
These vehicles use a pressure differential valve, a metering valve (1980---84) and a proportioning valve which are combined in a single unit. These valves sense unbalanced pressure between front and rear brakes.
Loss of pressure in either the primary or secondary brake system causes pressure differential valve to move off center and illuminate brake warning light. After system is replaced and brakes are bled, the valve centers itself, turning off warning light. The brake warning light switch is mounted on top of the valve body casting above the pressure differential valve tapered shoulder groove. When the valve is centered, spring loaded switch plunger fits into the tapered shoulder groove. The switch contacts are open, interrupting electrical continuity to the brake warning light on the instrument panel.
The metering valve is located in the front end of the control valve housing between the front brake system inlet port and the right and left front brake outlet ports. This valve regulates hydraulic fluid pressure to the front disc brakes.
The proportioning valve used on some models is located at the bottom of the housing between the rear brake system inlet and outlet ports. This valve regulates rear brake system hydraulic pressure. A plug and tube seat is pressed into the rear end of the central bore. A hole through the center of the plug and tube seal directs hydraulic fluid from the valve to the rear brake system outlet port.