What to know about the Proportioning / Combination Valve:
Your braking system relies on hydraulic pressure to function. When you depress the brake pedal, brake fluid is pushed through the system to the wheels. Fluid pressure is in charge of actuating both disc brake calipers, as well as drum brakes. However, there are numerous parts in line between the brake pedal and the brakes themselves, including the combination valve.
The combination valve is in controlof 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 essential 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).
Facts to Note:
In modern cars that employ combination valves, changing the entire valve body is necessary if the proportioning valve fails.
There is no way to check operation on this type of valve unless it has failed completely.
The valve may have failed due to many reasons, including debris in the brake fluid.
How to Fix:
The faulty proportioning combination valve brake lines are disconnected
The faultyproportioning combination valve is removed from the vehicle
The new proportioning combination valve is fixed and the brake lines are connected to valve
The brake system is bled and purged of air in the system and the brake fluid is refilled
The vehicle is road tested for proper brake operation
Follow your automaker’s recommendations on brake system service to make sure that the fluid is in good condition and free of debris. Have your braking system maintained by your expert mechanics to make sure that any potential problems are caught as soon as possible. Driving with a failing proportioning valve puts you at increased risk.
Common symptoms indicating you may need to change the Proportioning / Combination Valve:
Rear brakes lock up easily, particularly on wet pavement
Importanceof this service:
While it is still possible to drive with a failed or failing proportioning valve, it’s not recommended since it reduces 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 straightaway.