I bought a used 06 tC with 85k on it, 5-Spd manual. Previous owner said she had both front wheel bearings replaced. I got new tires on it yesterday in hopes it'd alleviate this concern but to no avail...now I just notice it more since the bad tires masked it previously.
At speeds greater than 45 mph you start getting feedback in the drivers floor board and can feel a slight vibration in the steering wheel. If you have neutral steering i.e. no input left or right, just sort of floating the wheel the sensation is reduced. If you give minor input
to change lane either direction the feeling increases dramatically. If you give a sharp abrupt input such as apexing an on-ramp to the highway, the sensation goes away.

I'd say it's a wheel bearing issue if I didn't know the PO replaced them. Now I'm wondering if it's something half-shaft related? It is not a tire balance issue, the ball joints and tires are tight, wheel bearing feels fine spinning by hand both with the wheel on and off.

Please help!!

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Do you think it's not a tire balance issue because you just replaced the tires? I will bet that's a bad assumption if that's your only reason you say that.

If you just had the tires replaced and then the vibration simultaneously got worse... 10 out of 10 chance that the tire shop did a bad job balancing. Take it back to the tire shop and tell them there's vibration that wasn't there before.

 

I'm an engineer for Goodyear, I'm positive it's not a tire vibration. I'm leaning towards something w/the half shaft.

 

Well I replaced the half shaft and there was no change. I am at a loss, any input greatly appreciated.

 

Well even though the previous owner said she did wheel bearings this august i'm going to replace the drivers front wheel bearing. This is driving me insane not figuring it out.
I do think the car has been in a slight wreck as the lower control arm on the drivers side has junkyard paint pen writing on it. No apparent structural damage anywhere though and original core support etc. but maybe something is tweaked.

 

Did you try rebalancing the tires yet?

If you have a vibration in the steering wheel that starts around 45mph, about 99% of these problems start and end with a wheel out of balance, so that is the logical place to start... especially since the tire shop who mounted your tires will do it for free. The fact that it started immediately after you had new tires installed makes it even more likely that they just did a bad job of it.

Wheel bearings don't really cause this sort of problem unless they have so much play that you are experiencing other, more drastic symptoms too.

 

Warped rotors can cause serious vibration as well

 

Did you ever figure it out?

 

On a different car that I had that gave me a vibration between 50mph and 60mph, it turned out to be my front shock absorbers.