Les-10

Thanks for your responses - yeah when i hit the bumps (or drops in pavement) you can distinctivey hear the front just normally absorb the impact & then the rear scrub or make contact with what sounds like the rotating rear tires. One of the spots where I hear this is just a block from my home, so I got a friend to stand on the street & watch me approach & hit the bump - he says the tires recoil up into the wheelwell a 1/4 inch maybe. When you push down on the rear bumper it's impossible to get the car to move down more than 3/8 of an inch or so. I am obviously overlooking something!

Bill Dearborn

Have you checked the wheels to see where they are laterally located in the wheel well? C6 widebody cars have one alignment adjustment point on the LCA and two adjustable dog bones on the UCA. You can literally move the wheel laterally in the wheel well and still maintain alignment. In other words, change the number of shims behind the UCA dog bones and then make a corresponding cam change on the LCA and the wheel will move in or out while maintaining the same camber, adjust the tie rod to maintain the toe setting you want. The left rear tire on my 08Z was slightly rubbing against the edge of the quarter panel opening and I was able to move it inward a 1/8 inch to get the tire to clear the quarter panel. Depending on the camber and toe settings you have there may be some rubbing on one side or both sides.

Bill

Les-10

Very interesting and logical. Will be digging into possibilities. Was not aware lateral positioning was adjustable. Thanks!

MswmSwmsW

This is great info! I have a tiny bit of rubbing on the front upper corner of the quarter panel on the left rear. I'll pass it on to the alignment shop when i have the rear tires changed in the next month or two.

Thanks!

Jfryjfry

Get the rear up in the air and use a Jack under the rlca to lift one side and turn the wheel to see if you can hear it.

You need to find witness marks to see what is being hit.

you could also possibly put a pair of front wheels/tires temporarily on the rear and see if it persists.

Les-10

Was excited about your easy to do suggestions:
1) Placing a floor jack under one side lower control raised the suspension such that the fender gap above the tire increased big-time, so no contact.
2) Borrowed a pair of fronts (285s) from a friends C6Z & there was absolutely no rub/scrub nothing at my rear, so there's that!

Thought I saw a slight witness mark on passenger side top front of fenderwell where the panel goes in to a point, put some chaulk on it, no transfer to tire. SO I do have contact
somewhere & I have just not been smart enough to find witness marks which is a necessity I know. Thanks

Les-10

First,Thanks to all that offered suggestions. After unsuccessfully using paint sticks & shoe polish to help find some witness marks of rubbing, I thought about the possibility of the sway bar bushings as the source of the noise. When I disconnected the end links I could hardly get the bar to budge. I removed the swaybar assy & lubed the inside of the bushings with dielectric "grease". After re-assembly the noise was finally gone. I have done a lot of reading about sway bars & it seems there are 2 different schools of thought as to lubing them. So in summary I'm not sure if the noise was the result of insufficient lube or the bushings are worn which allows the bar to rotate within the rubber causing the noise. Either way, I'm in much better shape than I was. I apologize for mistaking the sound as tire scrub but I swear it sounded like 2 distinct contacts in the wheelwells. The only thing I don't understand is why I did not hear the noise from the smaller 285s from the front of my friend's 08Z. Thanks again, Forum is Great!

Apocolipse

Great to know - thanks for the follow up!

Jfryjfry

The bar turns within the bushings, it’s how they work. There are different schools of thought based on the bushing material but generally you want the bar clean and smooth and the bushings in good condition. You shouldn’t have any issues if this is the case.

if you have a larger rear bar than what came with it, make sure the bushings are matched. I could see someone mistakingly using stock bushings with a larger bar which would result in binding , assuming you could even get it all assembled.