Without ABS

Proportioning Valves For Non-ABS Vehicles:

CAUSES
If premature rear wheel skid occurs on a hard brake application, it could be an indication that a malfunction has occurred with one of the rear brake proportioning valves.

TESTING
One proportioning valve controls the right rear brake, and the other proportioning valve controls the left rear brake. Therefore, a road test to determine which rear brake slides first is essential. Once the wheel which slides first is determined, refer to procedures to diagnose the proportioning valve. The test procedure for a premature rear wheel skid is the same for both rear wheel proportioning valves. The pressure test fittings used for each proportioning valve though are different due to proportioning valve and brake tube nut thread sizes being unique for each rear wheel. After road testing vehicle to determine which wheel skids first, the proper test fittings required will have to be determined. Then refer to procedures for testing the required proportioning valve.