I’ve racked countless cars also and it’s not a common problem but does happen sometimes.
The strut that failed on my car had actually been replaced along with the other side and the struts had less than 40k miles on them.
It rode fine before the oil change and bounced like a ping pong ball immediately afterwards. It even failed the left front bounce test which is not always a true indicator of a strut’s condition.
The strut theory (and it’s only a theory) is the only thing I can come up with at the moment beause I’m having a near impossible time seeing multiple tires and balancings not curing a problem that did not exist previously.
The only other theory might be that the wheel balancer at the tire shop is out of calibration. A dealer I worked for bought a new Snap On balancer and that thing was nothing but a boat anchor from Day One. After several days every mechanic in the shop including myself refused to use it.
Tolerance was usually under a pound; at least in most cases. Seriously.
Did you ever find a fix for this??? I have just purchased a certified 2010 G37x coupe which has the exact same issue. The dealer had just put on 4 of the same Goodyear tires you had put on and has re-balanced them 4 times…each time it rides smooth for about 1-2 weeks, then starts shaking again over 70 mph. I saw where there was a service bulletin on vibration caused by the rear drive shaft which I will have them check next.
Just a comment on the shocks. I had the rear shocks go bad on me on my Riviera when it was hoisted up. I must have had 300K on them though but they were hard as a rock but didn’t have any vibration from them, just a bone jarring ride. The problem was that they were air shocks with the suspension system. Had to switch them out to manual air shocks. So it does happen from time to time.
Driveshaft has been changed along with one of the front CV shafts and re-balanced again to no avail… Now 2 different Infiniti Dealers in Houston have tried to fix it and have now said that some “shaking” is normal in the coupes… I simply cannot believe that… The 4 door loaner G37’s they have been giving me ride smooth as glass… This is enough to make me never want to buy another Infiniti… I have always had Hondas and Acuras before this and this was never an issue.
