The dual proportioning valve, located between the rear brake system inlet and outlet port, controls the rear brake system hydraulic pressure. When the brakes are applied, the dual proportioning valve reduces pressure to the rear wheels and provides balanced braking.
If the rear brakes lock-up during light brake application or do not lock-up under heavy braking the problem could be with the dual proportioning valve.
- Check tires and tire pressures.
- Check the brake linings for thickness, and for contamination by fluid, grease etc.
- Check the brake system hoses, steel lines, calipers and wheel cylinders for leaks.
- If none of the proceeding checks have uncovered any problems, suspect the proportioning valve.
Take the car to a qualified service center and ask them to do a pressure test on the valve. If a pressure test is not possible, replace the control valve.