Proportioning Valve
If premature rear wheel skid occurs on hard brake application, it could be an indication that a malfunction has occurred with proportioning valve portion of combination valve.
To test proportioning valve when rear wheels of vehicle slide (lock up) first, leave front brakes tubes connected to combination valve, and proceed to test proportioning valve for rear brakes as follows:
- Remove brake tube coming from master cylinder at combination valve. See Fig 2
. Remove brake tube going to rear wheels from combination valve.CAUTION: Pressure Test Fittings (Special Tool 8187) have different size tube fittings. Be sure pressure test fitting being installed in combination valve has correct thread sizes for installation in combination valve and installation of brake tube fitting.
- Install correct Pressure Test Fitting (Special Tool 8187) into port of combination from which master cylinder brake tube was removed from. See Fig 2 . Install correct Pressure Test Fitting (Special Tool 8187) into port of combination from which rear wheel brake tube was removed from. Install Pressure Gauge (Special Tool C-4007-A) into each of Pressure Test Fittings (Special Tool 8187). See Fig 3 .
- Have a helper exert pressure on brake pedal (holding pressure) to get a reading on valve inlet gauge and check reading on outlet gauge. If inlet and outlet pressures do not agree with values on following chart, replace valve.