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Mysterious Sound – Vacuum Leak? by gem1138
Started on: 12-24-2009 10:05 AM
Replies: 3
Last post by: 2farnorth on 12-24-2009 03:07 PM
gem1138
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Report this Post12-24-2009 10:05 AM Click Here to See the Profile for gem1138Send a Private Message to gem1138Direct Link to This Post
88GT w/Auto

Last night I was braking for a red light and my daughter comments that there’s something wrong with my brakes. I was listening to a sound that was like nothing I remember hearing from a car before. It was like a high pitched vocalization.

My first thought was that the diaphragm in the brake booster has a pinhole leak. The sound continued for almost a second after the car came to a stop, eliminating the possibility that the brake pads, just six months old, were responsible for this rude sound.

My second thought was that it might be the bearings in the circulating fan, 18 months old, producing this sound because of the forward thrust resulting from deceleration. I turned the fan from medium to low and the next time I stopped the sound repeated unchanged so I returned to my first thought.

It happens intermittently, not every time I stop. This morning I stopped at a light, engine cold, and while sitting there, foot on brake, in drive, the sound presents itself. So, as a test, I moved the selector into neutral and took my foot off of the brake to no effect on the sound. A few seconds later, the sound faded below audibility.

I am still thinking booster diaphragm or some other vacuum hose associated with the booster. The sound seems to be coming from somewhere up front but it is hard to pin point.

Does this sound familiar to anyone? Got any brilliant ideas?
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Phil
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Report this Post12-24-2009 10:35 AM Click Here to See the Profile for PhilSend a Private Message to PhilDirect Link to This Post
One of the tests for checking your booster is to step in the brakes after the car has been shut off for awhile, you should get about 3 or 4 pumps of the pedal before the pedal feels different. Then while still holding the pedal down start the car and the pedal should go down farther. OR start the car for a minute or two - shut it off wait a few minutes then VERY CAREFULLY remove the black plastic check valve on the booster and you should hear a big woosh ( meaning that the booster is holding vac).
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gem1138
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Report this Post12-24-2009 11:08 AM Click Here to See the Profile for gem1138Send a Private Message to gem1138Direct Link to This Post
Thanks Phil.
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2farnorth
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Report this Post12-24-2009 03:07 PM Click Here to See the Profile for 2farnorthSend a Private Message to 2farnorthDirect Link to This Post
My heater fan has a bushing going bad and will cause a high pitch whine at times. I notice the changes in pitch when braking, accelerating, turning left or right. The sound seems like it's directly in front of me when driving and that would fit the location also.
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