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Random Hiss under braking

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Old Apr 11, 2018 | 10:02 PM
  #1  
Lowkey918's Avatar
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From: California
Random Hiss under braking

Hi everyone,

I just picked up a 2014 Evo X GSR with 45k miles on it and I've heard this hiss twice in one day and was wondering what it could be. I tried searching the forums but couldn't find any threads that match what I heard.

When I am applying light brake pressure I would hear what sounds like air being released when I'm nearly stopped. The sound reminds me of a BOV or a semi truck engaging it's parking brake.

However, the sound doesn't consistently happen and I couldn't replicate it when I tried, but I have heard it twice in one day.

The only thing that remained consistent was that I was driving the car for some time. First time it happened was after cruising on the freeway for 30 miles and the second time was cruising on the freeway for 8 miles.

Any help is appreciated.

Thanks.
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Old Apr 11, 2018 | 11:54 PM
  #2  
DeweyD's Avatar
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From: IL
Could be a brake booster vacuum line or maybe an issue with the booster itself.
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Old Apr 12, 2018 | 03:16 PM
  #3  
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From: l
Just gonna throw this out there, but have you checked the brake pads for wear? Foreign object? Does the pedal require a lot of force to bring the car to a stop?
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Old Apr 12, 2018 | 10:04 PM
  #4  
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The brake pedal does feel very stiff, it doesn't travel far and requires a lot of pressure to press down further...could it be air in the hoses? The car stops very well still and doesn't require much pressure to come to a complete stop or for the brakes to bite hard.

I brought the car into my local dealer for inspection and the tech noted that the brakes will need to be changed soon, there isn't a lot of meat left on the pads.
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Old Apr 12, 2018 | 10:14 PM
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DeweyD's Avatar
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From: IL
If the pedal is stiff then it's not air in the lines. If that were the case then the pedal would be mush and the car would barely stop. Still sounds to me like a brake booster issue, either vacuum lines going to it or the booster itself. This is what gives you the power braking. Does it basically feel like you have no power brakes?

this would also account for the pressurized hissing noise you described
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