2006 Legacy Vibration Through Gearbox & Driveline

Tell me this, if you can: did your car have impact to the underside recently? If so, then your Subaru may have a problem that is not apparent to you. Let’s say your Legacy struck a rock or log while you may been beating a trail in the outback. You may not have even felt it at the time, however, it may be that there could be a dent in bellhousing that is forcing transmission fluid to flow incorrectly. That said, it is possible this is the cause of your vibration.

I do agree with your technician’s general comment that your Legacy might fail today or it could go 200,000 more miles with the vibration thrumming through through the vehicle’s structure. It’s a true statement. Indeed, the chances are good, though, that you will have many more miles ahead before the failure.

As to the other possibilties, the still revolve around an impact that you may not have felt but which has caused the vibration. It is possible that the input shaft was forced out of round due to an impact on the input side gearing. If this is the case, then, your transmission will act exactly as you describe. It’s also possible that one of the half-shafts taking the power from the tranny to the wheels (front or rear it doesn’t matter in an AWD vehicle) has been forced out of round by an impact, as well.

It is also possible that the differential is out of round (there can be a lot of that going on in a transmission if an impact is big or hard enough) so that the output shafts are vibrating as well.

Finally, I’d have the technician take a close look at the gearing. If the gearing is again out of round, then you have a problem.

Since the problem could be in one of several areas, I would think an OBD-II diagnostic is the first order of business to start to narrow down the location of the problem. Since you do have a bit of time before anything serious might happen you can take your time and find out the exact problem before committing to it. Good luck and let me know what happens.