The proportioning valve or the combination valve is an integral component in any automobile’s braking system. It is the part responsible for the ensuring brake balance or controlling the front and rear brakes. Because you cannot apply the same pressure at the same time on both the front and rear brakes which can result in the rear brakes locking up, the proportioning valve makes sure that only a specific amount of pressure is applied on the rear brakes. The proportioning valve is usually the part that connects the master cylinder to the entire braking but in some models, it is not necessarily dependent on the cylinder.

Proportioning valves are also important in ensuring brake balance in the vehicle. A faulty proportioning valve may be potentially dangerous because it pressure may concentrate on the rear brake when the vehicle decelerates hastily or too quickly. Heavy braking, which at times can be inevitable, can lock up the rear brakes of the vehicle so a functional proportioning valve in top shape is crucial.

The proportioning valve is loaded with a spring. It is activated once you press on the brake pedal through the build-up of fluid pressure. The plunger on the valve then dismounts and fluid flows into the calibrated range. Next, the spring in the valve is squeezed and the plunger deters any more fluid from getting through. For the safety of the driver and the passengers, it is important that the pressure is evenly distributed on the front and the rear of the vehicle.

It’s important as well to know which type of proportioning valve fits your vehicle’s brake system. This way, when the time comes that you’ll need to replace it, you’re more informed and the purchasing process is simplified.

1.       Master Cylinder-Mounted

This type of proportioning valve is mounted right above the cylinder. They are also hooked up on the fluid ports which are found in between the cylinder and the braking system.

2.       Load Sensing

This type of proportioning valve is found on the frame of the rear of the vehicle itself. It features a lever that connects to the suspension of the vehicle.

3.       Combination Valve-Mounted

This type of proportioning valve is a mere piece of the combination valve along with the pressure differential switch and the metering valve. You will find this valve either on the frame or on the inner fender right under the master cylinder.

1.       Two-way valves

These valves are identified by their roughcast housing. It may have a combination of either: a proportioning valve and a pressure differential switch or a metering valve and a pressure differential switch.

2.       Three-way valves

On the other hand, these valves can be identified by their aluminum housing which contains a combination of a proportioning valve, a metering valve and a pressure differential switch.

Because the proportioning valve is an integral component of the entire brake system, it becomes vital to be aware of certain symptoms once it starts to fail. Having knowledge of the signs of a deteriorating valve can save not just your vehicle, but the lives of the driver and the passengers as well.

1.       Car nose dives when you break

As mentioned, the proportioning valve controls the amount of pressure applied on the rear brakes. So a dysfunctional valve will throw of the optimal amount of pressure towards the rear brakes of the vehicle. The sudden inertia of the halt pushes the front part of the vehicle forward because of the sudden loss of momentum.

2.       Car does not halt immediately when braking

Again, a problematic proportioning valve will throw off the brake balance. Thus, the vehicle may not receive enough pressure once it does brake.

3.       Rear wheels start to lock up

Because the proportioning valve is responsible for decreasing pressure to the rear brakes, a faulty valve has the tendency to cause rear wheel lock-ups when braking. These are more common on wet surfaces and you’ll notice a different feel to the rear brakes even when you brake gently.

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