vibration problem
 

the car is my 2015 RS,just back from the body shop last week.it rides good at speeds under 65 but when you take it to 70 or beyond it get a shake in the steering wheel and the passenger side seat vibrates.it has 4 new tires on stock wheels.not a huge lets depart the road and crash kind of shake but it wasnt there before.suggestions on my next step? i have already emailed my insurance adjuster.

That and contact the people that did the actual work on the car.

yep...

Something is bent that probably wasn't visible

im thinking axle shaft,the car was pushed sideways by a semi for about 1/4 mile.called the body shop.since 3 new tires were mounted and balanced last week they want me to have the tire shop check balance and alignment first.im thinking that they could put it in gear and run it up to 70-75 on the rack while its there and find the culprit.(which i still believe to be axle shaft.the body mechanic visually checked the underside of the car but it wouldnt take much of a wobble to cause vibration.

Yours doesn't have a solid axle shaft like the older cars do. You have CV axles and a hub mounted to a knuckle. Possible for one of the hub flanges to be bent but I would think you'd have bearing noise if that were the case. Most likely it tweaked a wheel which may only be found by measuring runout. If it's only happening at around 70 the run out would be minimal. Also, one of the new tires could have a internal problem....not unheard of

Right, the half shaft CV’s only spin at wheel speed. Being almost completely machined and relatively small in diameter, they shouldn’t cause a problem - unless bent badly. Fought many an out of round tire. You could put a SQUARE tire on a balancer and it would balance out fine. But it wouldn’t roll very well. If ya know wut a mean.

so how would the shop find a bad tire?

There are pretty sophisticated vibration analyzing tools as you are no doubt aware of, 45, but when someone complains of steering wheels and seats shaking, those are typically associated with larger, lower frequency (wheel speed) inch-ounce vibrations than say a driveshaft (or torque converter/ differential) spinning at 2-3000+ RPM. It would be more up to a tire shop to diagnose a tire problem but…in my experience, it has been difficult getting them to admit that it is indeed their tire problem.

I’d be willing to bet he could ‘drive-through’ the vibration where it might go away at say, 80mph or higher. The ol harmonic thing. If more than one tire is out of round, I have seen them get ‘sync’d up’ and cancel the vibration where the it goes away but comes back as the vehicle turns and the relative position of the tires change due to the differing radius’ of turning. If that happens, it’s definitely tires.

If you have a buddy with a camaro, swap wheels and see if it goes away.

You could look for a shop that can check tire runout. I had one tire with excessive runout and it would vibrate above 70. The tire would balance fine but still vibrate.

When i had the vibration i made a list of possibilities and went through them from cheap and easy 1st and worked my way toward hard and expensive. I had a combination of issues.

the car was fine until it was hit by a semi truck.drivers side rear wheel and tire were replaced and i thought i noticed vibration on the way home but figured it was from at least one of the other tires being flat spotted.3 new tires later...problem is still there.im thinking its got something to do with drivers side rear .@fz4k98...was it the wheel or tire that was defective?oh yeah,took it out of gear into neutral at 75 and vibration was still present,wouldnt that rule out drivetrain?

I did a rotor job but can’t recall. (give an old man a break!) Isn’t there a 5-bolt hub that the rotor bolts to? Seems a hit there could tweak the hub. That would wobble the hell out of a tire and wheel. Remember, what looks like a little bit of face-of-hub runout on a 4” (or so) dia hub is much, much greater by the time it reaches the OD of a tire and wheel bolted to it.