The car is a 2006 Outback XT, 5 speed manual, 90k miles, stock except Cobb DP and Stage 2 tune. These symptoms started several thousand miles ago and have gotten worse:
- Very noticeable shaking of the shifter when driving 20-25 MPH regardless of which gear is selected, can also feel shaking in the steering wheel and seat
- Roughness (higher frequency vibration) when driving 60 MPH
- Roughness when accelerating hard, immediately smooths out when releasing the accelerator (no power loss - car pulls hard).
The symptoms are not tied to engine speed, so I figured it was related to a driveline component. The wheels/tires are fine, no misfires or other engine codes. The symptoms are present, but much less noticeable, during the first mile of driving when the car is cold. The transmission mount looks normal (no cracks/tears), the engine doesn't budge when I try rocking it (can't get a good visual on the engine mounts). The driver side front halfshaft is an OEM Subaru shaft with around 30k on it, the passenger side is a rebuilt aftermarket shaft with around 40k on it.
Thinking a bad U-joint was the most likely culprit I had the driveshaft replaced with a new OEM shaft. There was no improvement. So now I'm wondering if the passenger side halfshaft is bad, the transfer case/viscous coupling is bad, or there's some other cause. I need to visually inspect the rear diff mounts but I didn't notice them being torn previously.
Any reference I've found on the forums with similar symptoms ended up being fixed with a new driveshaft or front halfshaft. I mention the transfer case since that first mile isn't as bad as when the car warms up.
Thanks for any suggestions,
Zack