Combination (Proportioning) Valve

If premature rear wheel skid occurs on hard brake application, it could be an indication that a malfunction has occurred with the proportioning valve portion of the combination valve.
To test the proportioning valve when the rear wheels of the vehicle slide first, leave the front brakes tubes connected to the combination valve, and proceed to test the proportioning valve for the rear brakes as follows:






1. Install one gauge and (TEE) from Special Tool C-4007-A between the brake line from the master cylinder secondary port and the combination valve.
2. Install the second gauge from Special Tool C-4007-A to the rear brake outlet port on the combination. Gauge is to be attached to the combination valve using an adapter tube made from a short piece of brake tube and (1) 3/8 x 24 tube nut, and (1) M10 x 1 tube nut. Connect the hose to the valve. Bleed the hose and gauge.
3. Have a helper exert pressure on the brake pedal (holding pressure) to get a reading on the valve inlet gauge and check the reading on the outlet gauge. If the inlet and outlet pressures do not agree with the values on the following chart, replace the valve.





PROPORTIONING VALVE PRESSURE SPECIFICATIONS