Transient Vibration - Dorkiphus.net

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Old 07-09-2018, 11:05 AM
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Default Transient Vibration

On my 996 Race Car I have been chasing a vibration/shaking issue to no avail. The vibration comes on only between ~85-95mph then goes away. It started about a year ago but i cant correlate it to any changes in the car and it has not gotten any worse over the year. From the drivers seat it feels like its coming from the body of the car - not the wheels as the steering wheel isnt shaking.

- problem occurs at these speeds regardless of gas/brake/coast
- braking is smooth without shudder and replacing rotors had no impact
- problem occurs regardless of which wheels I have on the car
- all four wheel bearing have been replaced this year
- all suspension parts are tight and i dont see any worn bushings.

Ideas?
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Old 07-09-2018, 11:46 AM
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Quote:
Originally Posted by BikePump View Post
Ideas?
Go see Charlie
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Old 07-09-2018, 11:51 AM
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Go see Charlie
in classic Charlie fashion he told me to "stop complaining and drive the car" last fall. i am taking it in for another issue next week but if I can troubleshoot and deal with it myself thats a good thing.
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Old 07-09-2018, 12:06 PM
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You could try putting a dial indicator on each wheel hub. Maybe you have one that is slightly bent.
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Old 07-09-2018, 12:22 PM
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Quote:
Originally Posted by BillC View Post
You could try putting a dial indicator on each wheel hub. Maybe you have one that is slightly bent.
we have checked to make sure that the hubs are straight (sorry left that off the list). it seemed like an unlikely candidate given that the vibration only appears in that one narrow speed window.
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Old 07-09-2018, 01:25 PM
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You appear to have eliminated almost everything with your testing - good job. I'm going to say axle(s). They appear to be the only thing spinning that would only appear at a specific speed (as opposed to Engine RPM). Coming from the car (and not your hands) would further indicate the rear of the car.

Otherwise I will go with Pucker Flutter
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Old 07-09-2018, 01:31 PM
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axle was my guess also...had a similar problem on a van once though at lower speed....
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Old 07-09-2018, 02:05 PM
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Check all the plastic under trays and fasteners. Check the 1/2 shafts. Check all the motor and trans mounts for both bolt tightness and condition of the rubber/ isolation system.
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Old 07-09-2018, 02:37 PM
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Don't go below 95 mph...
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Old 07-09-2018, 03:02 PM
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<Hagar voice on > “I Can’t drive....... 95!”
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"There is grandeur in this view of life...." Darwin.

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“The earth has music for those who listen”
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