As the title says.... I have noticed that my sons GTA shifts from side-to-side once in a while while driving. I noticed this a few days ago when I was driving behind him. AND I noticed yesterday that the outter treads on the rear tires are wearing unevenly.

And ideas, suggestions ???

 

Sounds like axle-walk. Could be bushings in the rear too.

 

Bushings ??
LCA's and panhard bar, correct ?

 

Yes. Check all bushings holding that rear end on. Lower Control Arms, Panhard Bar (check brackets too) Sway Bar End Links.

 

Push sideways on a rear fender. If the car moves sideways at all and maybe clunks then most likely the PHB is loose but check the other stuff too.

 

Put a big feather in the backhatch and turn up the music

Seriously,
Most likely bushings: panhard bar, lower control arms, shocks can get sloppy, and torque arm. Those are the only attach points.
Worse case: axles.

 

Okay so I went out and pushed on the fender.... the entire car shakes, no noises at all. The back of the car seemed very tight.

Could it possibly be something as simple as bad shocks ??

 

Put a big feather in the backhatch ???

 

I had once not used a tiny bit of thread locker on the Panhard bolt, and it had backed off enough to allow about a millimeter worth of play.

I could FEEL it the minute it backed off. Crossing over a crown in the road, or any time the camber of the road changed the back end of the car would shift.

Needless to say I used a bit more thread lock on it. The thought of losing the PH bar at speed scares the crap out of me. If that happens no amount of skill will control the car, you are going along for the ride.

Make sure all the suspension stuff is tight.