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What Is a Brake Proportioning Valve?

A brake proportioning valve underneath a brake master cylinder

The brake proportioning valve is a key part of your brake system. It’s responsible for ensuring that brake force is properly applied when you step on the brake pedal. If it doesn’t work, your car will not slow down as expected. This problem requires immediate attention.

Here’s how a brake proportioning valve works and how to determine if yours needs to be repaired.

It’s All About Brake PressureBrake Proportioning Valve

Each time you press on the brake pedal, there are four wheels that need to be slowed. It might seem like they all respond at the same rate, but equal pressure can’t be applied to all the wheels at once because it would cause the rear wheels to lock up.

The brake proportioning valve controls the pressure between your front and rear brakes to make sure a rear lock up doesn’t happen. It does this by regulating the amount of pressure that goes to your rear brakes. Those brakes still engage when you press the brake pedal, just with less force than your front brakes. This ensures smooth and even stopping every time.

Signs of a Problem

The biggest symptom of a failing brake proportioning valve is your rear wheels locking up when you apply the brakes. This might be something you feel, or you might hear it if the rear wheels squeal when they lock up.

One way to test for this problem is to find an empty parking lot or flat surface and ask a friend to watch your car from a safe distance as you make a few medium-to-hard stops. If the rear wheels lock while the front wheels keep spinning, then the problem is confirmed.

Get the Issue Fixed Quickly

Brakes that function properly are an essential part of your car. They keep you and everyone around you safe. If you think your brake proportioning valve is failing, you should seek repairs immediately. Whether you take this on yourself or call on your local mechanic, you’ll want to handle the job quickly to ensure everyone’s safety.

Check out all the brake repair products available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information about brake repair, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy Wikimedia Commons.

Nicole Wakelin View All

Nicole Wakelin covers the automotive industry as a freelance journalist for a variety of outlets. Her work includes news pieces, podcasts, radio, written reviews, and video reviews. She can be found in The Boston Globe, CarGurus, BestRide, US News and World Report, and AAA along with lifestyle blogs like Be Car Chic, The Other PTA, and She Buys Cars. She is active on social media with a large following on both Twitter and Instagram and currently serves as Vice President of the New England Motor Press Association.

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