The fact that the vibration has changed from the steering to the seat tells me either you have a tire balance problem, bent rim, or a bad tire (belt shift, flat spots.).
Since the vibration is worse under acceleration turning right, then chances are it is (now) the left rear tire that is causing the problem. Think about it. When turning right, more weight is distributed to the left side of the car, so the vibration will be more pronounced.
I recommend checking that tire specifically, but it still could be either.
Let me know what you find.
Thursday, October 22nd, 2009 AT 8:39 AM