hissing sound when releasing foot off brake
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2017 C63s converitble
hissing sound when releasing foot off brake
Lately my car has been making a hissing sound coming from the brake pedal when i release my foot off. its also been blistering cold here.
are these 2 things related? or....?
are these 2 things related? or....?
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Joined: Sep 2016
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From: Australia
⏱️ 700HP Facelift converted C63 S Coupe with Drexler 3.06 plated LSD
When you're at a stop, if you creep forward and slowly apply the brake can you hear any creaking? Wind down all windows and try and listen. Or is it just this "hissing" sound?
Thread Starter
Junior Member
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2017 C63s converitble
i will give it a go next time im in the car, temperature has been below freezing here for the past 2 weeks
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W205 C63 S
I also have that sound and honestly I didnt think much of it until I saw your post. You get the hissing sound after you quickly release the brake pedal as if the pedal is going back to its original position right? This is what AI had to say when I looked it up:In many cases, a brief, momentary hiss immediately after releasing the brake pedal on a 2017 Mercedes-Benz C63S AMG (W205 chassis) is considered normal operation, but a continuous hiss is a sign of a leak.
Here is a breakdown of how to tell the difference between the standard vacuum release and a potential failure.
Here is a breakdown of how to tell the difference between the standard vacuum release and a potential failure.
1. The "Normal" Sound (Vacuum Equalization)
The brake booster in the W205 C-Class platform uses engine vacuum to assist your braking.- What happens: When you release the pedal, the booster vents atmospheric pressure to equalize the vacuum chambers.
- The Sound: It sounds like a quick "whoosh" or exhale of air that lasts only a second or less as the pedal returns to the top.
- Verdict: If the noise is short, consistent, and your braking performance feels normal (not hard or spongy), this is likely just the booster "breathing" and is a known characteristic of this car.
2. The "Problem" Sound (Vacuum Leak)
If the sound differs from the description above, you may have a leak in the brake booster diaphragm or the vacuum line connecting the booster to the engine.- Symptoms of a leak:
- Continuous Hiss: The sound continues for several seconds or doesn't stop until the engine is turned off.
- Pedal Feel: The brake pedal feels unusually hard to press (loss of power assist) or softer/spongy.
- Rough Idle: Because the booster is connected to the engine's vacuum system, a leak can sometimes cause the engine to idle roughly or stall.
- Continuous Hiss: The sound continues for several seconds or doesn't stop until the engine is turned off.
Thread Starter
Junior Member
Joined: Feb 2025
Posts: 66
Likes: 0
2017 C63s converitble
I also have that sound and honestly I didnt think much of it until I saw your post. You get the hissing sound after you quickly release the brake pedal as if the pedal is going back to its original position right? This is what AI had to say when I looked it up:In many cases, a brief, momentary hiss immediately after releasing the brake pedal on a 2017 Mercedes-Benz C63S AMG (W205 chassis) is considered normal operation, but a continuous hiss is a sign of a leak.
Here is a breakdown of how to tell the difference between the standard vacuum release and a potential failure.
Here is a breakdown of how to tell the difference between the standard vacuum release and a potential failure.
1. The "Normal" Sound (Vacuum Equalization)
The brake booster in the W205 C-Class platform uses engine vacuum to assist your braking.- What happens: When you release the pedal, the booster vents atmospheric pressure to equalize the vacuum chambers.
- The Sound: It sounds like a quick "whoosh" or exhale of air that lasts only a second or less as the pedal returns to the top.
- Verdict: If the noise is short, consistent, and your braking performance feels normal (not hard or spongy), this is likely just the booster "breathing" and is a known characteristic of this car.
2. The "Problem" Sound (Vacuum Leak)
If the sound differs from the description above, you may have a leak in the brake booster diaphragm or the vacuum line connecting the booster to the engine.- Symptoms of a leak:
- Continuous Hiss: The sound continues for several seconds or doesn't stop until the engine is turned off.
- Pedal Feel: The brake pedal feels unusually hard to press (loss of power assist) or softer/spongy.
- Rough Idle: Because the booster is connected to the engine's vacuum system, a leak can sometimes cause the engine to idle roughly or stall.
- Continuous Hiss: The sound continues for several seconds or doesn't stop until the engine is turned off.
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MBWorld Fanatic!
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2019 AMG GT R
mine used to do the same and i can confirm it indeed is because of the cold. Nothing to worry about
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Newbie
Joined: Mar 2014
Posts: 5
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From: Orlando Florida
2020 c63 amg
My 2020 c63 had this same hissing sound when releasing the brake pedal briefly and at times it would continue hissing after it being released. It was considered a vacuum leak by the dealership and fuel trims were all over the place aswell. Brake booster was replaced through the extended warranty,fuel trims stabilized and my mpg’s improved.
