Is this normal? Hissing from engine bay
Thread Starter
Burning Brakes
Joined: Jun 2017
Posts: 876
Likes: 197
From: Denver, NC
Is this normal? Hissing from engine bay
So I had the hood up yesterday after installing a new CAI. Car was idling in the garage. I also swapped new brake pads in, so I presses the brake pedal a few times to get some pedal feel. All of a sudden I started hearing this hissing or electric noise every time I applied brakes. Longer I presses, longer it went for. I took car to dealership and they said the sound is normal.
I have a video but no clue how to post it here. It's pretty loud and sounds like it's coming from the driver front wheel well area.
Out of curiosity, can anyone try to replicate this? Pop hood, start car, after 30 seconds hit the brakes and hold for like 5-10 seconds. I just want to know if it's normal or if dealership is incompetent.
Thanks
I have a video but no clue how to post it here. It's pretty loud and sounds like it's coming from the driver front wheel well area.
Out of curiosity, can anyone try to replicate this? Pop hood, start car, after 30 seconds hit the brakes and hold for like 5-10 seconds. I just want to know if it's normal or if dealership is incompetent.
Thanks
Safety Car
Joined: Dec 2009
Posts: 4,194
Likes: 305
From: Lake Havasu City Arizona
SoCal Events Coordinator
St. Jude Donor '12
Two possible issues. First you had the ac on and the compressor lines were dripping water onto the exhaust causing the hissing noise. Or...
You have a vacuum leak. In the case of a vacuum leak the car would be idling at a higher rpm. Stepping on the brake and hearing the hissing would tell me that the brake power booster might have a vacuum leak.
Keep up posted on what you discover.
You have a vacuum leak. In the case of a vacuum leak the car would be idling at a higher rpm. Stepping on the brake and hearing the hissing would tell me that the brake power booster might have a vacuum leak.
Keep up posted on what you discover.
Thread Starter
Burning Brakes
Joined: Jun 2017
Posts: 876
Likes: 197
From: Denver, NC
Well according to the dealership this is normal. I can't imagine that's normal.
I did a search and found an old post where someone mentioned about the ABS and it's a test that it's working? Something like that.
Unfortunately I don't know anyone local with a c7 to test this out.
And no, the AC was not on.
I did a search and found an old post where someone mentioned about the ABS and it's a test that it's working? Something like that.
Unfortunately I don't know anyone local with a c7 to test this out.
And no, the AC was not on.
Safety Car
Joined: Dec 2012
Posts: 3,875
Likes: 1,874
From: St. Louis Metro East IL
The round shiny cylinder in front of the brake master cylinder is an electric vacuum pump. The vac pump runs when manifold vacuum is not sufficient. Multiple brake applications at idle would reasonably be a case where the vac pump runs.
I guess you could have someone apply the brakes while you feel / listen to the vac pump. Never noticed the noise, but I have not done any brake work nor pumped the brakes while parked.
I guess you could have someone apply the brakes while you feel / listen to the vac pump. Never noticed the noise, but I have not done any brake work nor pumped the brakes while parked.
