My 2007 997 Turbo has an annoying vibration that I notice at speeds above 70mph. What’s strange is that the vibration is cyclic in intensity, alternating between a gentle shake and a stronger shake about once a second. Also, the vibration seems most noticeable when I’m driving on certain grooved stretches of road — Iike perhaps the grooves are contributing to a resonance.
The vibration is relatively mild — a non enthusiast might not notice — I feel it through the body of the car (not the steering wheel) and it visibly shakes the passenger seat (cyclically).
It’s a drivetrain vibration that’s speed dependent. Changing to a lower/higher gear and/or pressing the clutch doesn’t change it, nor does accelerating or decelerating. I don’t hear any noise, and driving in tight circles in either direction is quiet.
Things I’ve tried:
- New tires (MPS4S) that have been road force balanced three times, by different shops (no change)
- I pulled the drive shaft from the trans to the front diff to see if there was a bad u-joint (no change)
- New transmission mount and driveshaft guibo (no change)
- Played with tire pressures between 30psi to 50psi (no change)
- I can’t feel any play in the wheels or axles/CVs when checked by hand
I downloaded a vibration app last weekend and logged some readings. Each of the charts below was a 5 second log with me driving at ~85mph. Doing the math based on my tire size (305/30 R19) works out to about 18.5 wheel axle revolutions/second at that speed — and coincidentally, that’s my 1st order frequency. But I’m also getting 2nd, 3rd, 4th, and 8th(!) order vibrations too (with hints at the other missing orders too) which has got me scratching my head.
Also, FWIW, my engine RPMs for this test were around 2900rpm or 48hz — and interestingly there’s a peak (though smaller) for that.
Let me know what you think.
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