Adjustable Upper Rear Control Arms

[gnvair]

Have your rims and tires Road Force checked with a Road Force balancer.
Just because your driveshaft shows no signs of missing weights does not mean it is not out of balance. A lot of G body shafts were marginal at best. They were acceptable with the non over drive transmissions, but a lot of vibration complaints showed up with the advent of of over drive transmissions. Is the vibration a new problem of something that just recently showed up?

 

[ed1948]

I've owned it for over three years, now at 90K miles, and it's always had vibration.

 

[gnvair]

Ok, I stand by my previous comments. Find a shop with a Road Force balancer and have all 4 wheels and tires Road Force checked. If they are ok then find a drive shaft shop and have the driveshaft balanced.

 

[pontiacgp]

I've owned it for over three years, now at 90K miles, and it's always had vibration.

have you raised the rear end off the ground and used axle stands under the rear axle and brought the car up to speed where the viaration occurs to see if you can see anything that is causing the vibration?

 

[GuysMonteSS]

I sure would like to see you find out what is causing this vibration.
Mine never had any issues,even with the 450 HP LS-6 BBC and the stock driveshaft when I first bought it.
It still even had the original U Joints ...
Guy

 

[ed1948]

have you raised the rear end off the ground and used axle stands under the rear axle and brought the car up to speed where the viaration occurs to see if you can see anything that is causing the vibration?

I attempted that by videoing the rear tires while sitting inside. I'll need to repeat that test with someone else operating the throttle.

 

[Rt Jam]

Good to see you checked for tire run out. It is often overlooked and ignored after it passes balancing.

The driveshaft and drums can be checked by holding the rear of the car up on axle stands under the axle housing. Remove the rear wheels and find open center wheel nuts to hold the drums on, make sure the nuts do not stop from a stud shoulder. Then spin it up to speed.