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Hissing noise when brake pedal is depressed Inspection Service

Brakes are the most important safety components on your vehicle. Despite that importance, it’s easy to take them for granted, at least until your car begins to do strange things. Ordinarily, pressing your brake pedal should result in only the car slowing down or stopping. If you hear a hissing noise when the brake pedal is depressed, it may mean there’s something that needs to be repaired in the system.

How this system works:

On many cars, the master cylinder works in tandem with a brake booster. The brake booster is mounted to the firewall, generally in front of the steering wheel position, and the master cylinder attaches to it. The entire point of the brake booster is to make it easier to press the brake pedal and slow or stop the car.

Your brake booster works on vacuum pressure. There’s a diaphragm inside that is responsible for maintaining pressure when you’re not pressing the pedal. However, when you do press the pedal, a push rod moves forward within the booster and into the master cylinder. The side of the diaphragm facing the cabin vents to atmospheric pressure, while vacuum is maintained on the other side.

This then equalizes with pressure on the other side of the diaphragm, providing the boost needed to make pressing your brake pedal easier. The hissing noise you hear when the brake pedal is depressed could be nothing more than ordinary operation, or it could be a sign of a deeper problem. There are a couple of different potential issues here, some more severe than others.

Common reasons for this to happen:

  • Leaking Vacuum Line: Your brake booster is supplied with vacuum from the engine via a vacuum hose. It’s usually located near the firewall. If this hose has a leak, it can be heard within the cabin.

  • Leaking Brake Booster Diaphragm: The diaphragm that’s responsible for maintaining pressure within the brake booster can fail, particularly if the master cylinder is leaking fluid into the booster. When this happens, you’ll hear a hissing sound when depressing the brake pedal, but the pedal itself will be much, much harder.

  • Damaged or Missing Foam Silence: Most cars equipped with brake boosters also have a foam silencer that’s designed to help prevent you from hearing that hissing sound. If the silencer has degraded or been damaged, you’ll hear the hissing sound.

  • Failing Master Cylinder: If you hear a hissing sound and suspect that the problem is the diaphragm in the booster, the actual cause is likely the master cylinder beginning to fail. Signs that the master cylinder is leaking into the brake booster include low fluid in the reservoir with no visible leaks.

What to expect:

A top-rated mobile mechanic will come to your home or office to inspect your brake system, including the brake pedal operation, the brake booster and listen to the hissing sound. The mechanic will then provide a detailed inspection report that includes the scope and cost of the necessary repairs.

How it's done:

The mechanic will need to crank the car in order to verify the hissing sound, and a test drive may be necessary to duplicate the complaint. Additionally, the mechanic will inspect the brake pedal operation, the condition of the brake booster, the master cylinder, the level of fluid in your system and more.

How important is this service?

Power brakes are wonderful things, making it far easier to work a brake pedal that would otherwise require significant force to activate. While the hissing sound may be a sign of nothing more dangerous than a failed piece of foam, it could be a symptom of something much more worrisome – a damaged brake booster and a failing master cylinder. You cannot afford to take chances with your brake system. One of our professional mechanics can inspect the entire system and determine if there’s cause for concern, and what needs to be done if there is a problem.

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Recent Hissing noise when brake pedal is depressed Inspection reviews

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YourMechanic Hissing noise when brake pedal is depressed Inspection Service

Average Rating

5/5

Number of Reviews

5

Rating Summary
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Chris

13 years of experience
150 reviews
Chris
13 years of experience
Chris quickly diagnosed my brake problem and will be back in two days to fix it. Very nice and professional. Good advice and recommendations as well!
2003 TOYOTA TACOMA - HISSING NOISE WHEN BRAKE PEDAL IS DEPRESSED - POWAY, CALIFORNIA

Richard

17 years of experience
43 reviews
Richard
17 years of experience
Richard was excellent! He contacted me in advance of the appointment to obtain more information about the problem in order to assist him in making a diagnosis, He contacted me a couple of hours prior to the appointment to see if he could come earlier. That worked for me because I had wanted an earlier appointment anyway. He explained the issue thoroughly and finished the job in a timely manner. I will recommend him to all of my friends.
2011 FORD F-150 - HISSING NOISE WHEN BRAKE PEDAL IS DEPRESSED - FORT WORTH, TEXAS

Breck

17 years of experience
314 reviews
Breck
17 years of experience
Breck was on time and very professional throughout. He inspected my car, identified the issue and then gave me background on the problem.
2010 MAZDA CX-9 - HISSING NOISE WHEN BRAKE PEDAL IS DEPRESSED INSPECTION - HOUSTON, TEXAS

Scott

33 years of experience
434 reviews
Scott
33 years of experience
Frendly, punctual, professional, and fast. Scott was a pleasure to work with and I'll definitely be using him as my mechanic going forward. Thank you Scott!
2005 HYUNDAI ELANTRA - HISSING NOISE WHEN BRAKE PEDAL IS DEPRESSED - PHOENIX, ARIZONA

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