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?

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.

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.

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 :)

axle was my guess also...had a similar problem on a van once though at lower speed....

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.

Don't go below 95 mph...

<Hagar voice on > “I Can’t drive....... 95!”