Used Brake Proportioning Valve

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A proportioning valve is a valve that relies on the statics to supply a reduced pressure to an output line.

A simple example is where spring load applies a reducing force so that the output pressure is reduced. Proportioning valves are frequently used in cars to reduce the brake fluid pressure to the rear brakes which are known as Brake Proportioning Valve.

The proportioning valve reduces the pressure to the rear brakes. Regardless of what type of brakes a car has, the rear brakes require less force than the front brakes.

The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.

If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force. If the proportioning valve were set to 70 percent and the brake pressure were 1,000 pounds per square inch (psi) for the front brakes, the rear brakes would get 700 psi.

Search for a junkyard that may have your Brake Proportioning Valve in stock! You can search in the USA by zip code for used auto salvage parts near you using our used parts request form.

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About Used Brake Proportioning Valves

The proportioning valve balances brake pressure between the front and rear to keep the rear from locking up, and a faulty valve can cause uneven braking or a warning light. A used valve is an economical fix.

What a Brake Proportioning Valve Does

The brake proportioning valve regulates how much brake pressure goes to the rear brakes compared with the front, preventing the rear wheels from locking up under hard braking. On many vehicles it is combined with the metering and warning functions in a combination valve mounted near the master cylinder.

Signs Your Brake Proportioning Valve Is Failing

Rear brakes locking up too easily, or braking too little
Uneven braking front to rear
A brake warning light from the pressure differential switch
A leak at the valve

What to Check When Buying a Used Brake Proportioning Valve

Confirm the valve is not leaking and the ports are sound
Confirm whether it is a standalone or combination valve
Check the switch and connector if it has one
Match the exact valve for your vehicle

Common Applications

Many vehicles use a proportioning or combination valve to balance the brakes. Internal faults and leaks are the common issues, and a used valve restores proper front-to-rear balance, matched to the vehicle.

Related Parts

Frequently Asked Questions

What does the proportioning valve do?

It limits how much pressure reaches the rear brakes relative to the front, so the rear wheels do not lock up first under hard braking. It keeps braking balanced and stable.

Do modern cars still have one?

Many older and mid-generation vehicles use a proportioning or combination valve, while newer vehicles often handle brake balance electronically through the ABS system. Confirm whether yours uses a valve.

Why is my brake warning light on?

The combination valve often includes a pressure differential switch that triggers the brake light if pressure is uneven, such as from a leak in one circuit. A fault at the valve can also cause it.