What is a Metering Valve?

Mary McMahon
Mary McMahon

A metering valve is a device found in the braking systems of vehicles with rear drum brakes and front disc brakes. The valve controls the distribution of pressure to the brakes to stabilize the car during braking, increase braking efficiency, and make braking safer. Metering valves are located at various points in the braking system, depending on the make and model, and may be part of a larger combination valve used to regulate pressure inside the hydraulic braking system.

The metering valve controls the distribution of pressure to the brakes when a person presses on their car's brake pedal.
The metering valve controls the distribution of pressure to the brakes when a person presses on their car's brake pedal.

When people apply the brakes in a car, they activate a hydraulic system that multiplies the pressure of their feet. A light tap on the brake pedal can translate into substantial pressure inside the braking system, allowing people to slow or stop the car. In a car with front disc brakes and rear drum brakes, if the pressure from the brake pedal went straight to the brakes, the front brakes would activate first, and this could make the car unstable.

If the front brakes kick into operation first, there is a risk that the rear of the car could fishtail or that other stability problems could develop. In a car with a metering valve, the valve diverts the initial pressure to the rear brakes, and once they kick in, pressure can be released to the front brakes and allowed to equalize. This happens within a very short period of time, and it can feel like the brakes are activating simultaneously.

Metering valves in cars compensate for the fact that disc brakes tend to activate more quickly and be more sensitive. In cars with other types of brake systems, a metering valve may not be necessary, or a different type of system will be used to control braking pressure so that the driver can apply the brakes safely. The metering valve works with a series of interconnected systems to keep the brakes working smoothly and properly when they are needed.

When brakes are checked, the mechanic may inspect the metering valve to confirm it is in good working order. If necessary, the valve can be cleaned or replaced. It is also important to remember to fully drain and clean the valve when the brake system is being flushed, and to properly reconnect all of the components of the braking system after work is finished. There may be special considerations with systems in individual cars as a result of unusual design features, including features intended to increase safety and efficiency.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


I know very little about cars, but I was just wondering whether the metering valve interacts at all with the anti-lock brake system?

I know anti=lock brakes are responsible for letting you turn the steering wheel and control the car while you are braking. I didn't know if the metering valve had to be able to accommodate this feature or if they are unrelated.

Also, is it possible for the metering valve to lose efficiency over time? Do they ever wear out to the point where brake pads might start to get used faster than they should because the metering valve is not operating at its maximum capacity?


@kentuckycat - Great question. While every car made today has disc brakes in the front, the rear brakes can be either disc or drum brakes. Basically the difference is that disc brakes use a rotor and press against the inside of the wheel while drum brakes use a set of pads that expand outward and push on the inside of a drum to stop the wheel from turning.

Disc brakes are usually considered more efficient since they are better at controlling heat and shedding water when it is raining. Drum brakes are cheaper, though. I assume the brake combination you have depends on the manufacturer and vehicle. I think most SUVs and trucks today use four sets of disc brakes.


I never realized there was so much involved after I pushed the brakes in my car.

First of all, what is the difference between disc and drum brakes? I always thought that most cars had four sets of disc brakes instead of discs in front and drums in back. I have had my brakes repaired and the mechanic talked about the rotors for all four tires. Do drum brakes also use rotors, or did my car just have four disc brakes?

How often do metering valves stop working correctly? I have never heard of it happening, but if it did stop working, would that mean you wouldn't be able to stop at all, or would you just not have the same amount of control?

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