Why Is There a Hissing Noise When I Brake?

  • Jun 16, 2021
Image of vehicle brakes Image of vehicle brakes

Snakes hiss. So do cats. But why are your car brakes making a hissing noise? Chances are, a mechanical issue is causing the hissing. Fortunately, in most cases, it’s an issue that can easily be fixed!

What’s Behind the Hissing Noise?

Cars can make many noises, and a hissing noise when braking can be among them.

You may hear a hissing noise if there’s a disconnected or leaking vacuum hose around the engine  or an issue with your vehicle's serpentine belt. But if you hear a hissing sound when pushing down or letting up on the brake pedal, it usually is caused by the brake booster leaking air, which could mean there’s a leak in the booster diaphragm, master cylinder gasket, or vacuum hose.

The brake booster relies on vacuum pressure to do its job. Inside the brake booster is a diaphragm that controls the pressure when the brake pedal isn’t pushed down. When the pedal is depressed, a rod moves into the brake booster and master cylinder. This step creates vacuum pressure on one side of the diaphragm to support stopping power. 

If something goes wrong with that process, it could lead to a hissing noise. The cause may be:

  • A hole in the vacuum hose that works in conjunction with the brake booster.
  • A problem with the booster diaphragm triggers the failure of the brake booster.
  • A leak of air from the master cylinder gasket into the brake booster.
  • A missing or damaged foam silencer. Many vehicles that have brake boosters come with a piece of foam that blocks the hissing sound. If the foam is missing or damaged, you may hear the hissing sound.


What Should You Do About a Hissing Noise?

If it seems that the hissing noise is connected to braking, don’t ignore it and hope the sound just disappears. Your car’s brake system is complex, so it’s best to take your car to the nearest Firestone Complete Auto Care where one of our technicians can perform a diagnosis to pinpoint the hissing noise, and recommend any necessary repairs. 

Our technicians can help determine whether the hissing can be blamed on something as simple as a missing or defective piece of foam or whether you’re dealing with something more serious, such as a brake booster or master cylinder that needs to be repaired or replaced.

It’s wise never to put off taking care of an issue with the brakes since the brakes are among your car’s most important safety features. Taking care of your brakes can ultimately lead to taking better care of yourself and your passengers.

When it comes to your car’s brakes, you should get regular brake maintenance before a hissing noise or anything else becomes a problem. According to a survey by research company IMR, at least one-third of motorists wait until some sort of brake failure happens before seeking brake service. At that point, the price tag for ensuring your brakes are working properly could be pretty hefty!

Your engine might be purring, but if your brakes are hissing, then your vehicle isn’t as road-ready as it could or should be! Visit your nearest Firestone Complete Auto Care to get a free brake inspection and high-quality car care.

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