Your braking system relies on hydraulic pressure to operate. When you depress the brake pedal, brake fluid is pushed through the system to the wheels. Fluid pressure is responsible for actuating both disc brake calipers, as well as drum brakes. However, there are numerous components in line between the brake pedal and the brakes themselves, including the combination valve. The combination valve is responsible for metering fluid to disc brakes, as well as fulfilling tasks done by both the pressure differential switch and proportioning valve (which is responsible for reducing the fluid pressure in the lines leading to the rear drum brakes). This is necessary because of how brakes work in terms of lockup – the more weight there is on a wheel, the more force can be applied without locking up the brakes. In rear drum brakes, the weight on the wheel is comparatively small (the weight of the engine on the front wheels is considerable).
Follow your automaker’s recommendations on brake system service to ensure that the fluid remains in good condition and free of debris. Have your braking system maintained by our expert mechanics to ensure that any potential problems are caught as soon as possible. Driving with a failing proportioning valve puts you at increased risk.
While it is still possible to drive with a failed or failing proportioning valve, it’s not recommended because it decreases your safety while increasing the risk of being involved in an accident because your rear brakes lock up under even light loads. Have the entire combination valve assembly replaced immediately.
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