350350

I've had a lot of cars (most of them junk) and I've never had any vehicle do this.

At about 110mph, it starts wobbling like a trailer that's not loaded right. It quickly escalates and if you don't back off, it would completely go out of control. left/right/left/right/left/right rapidly. The steering wheel feels solid while it does this. Pavement makes some difference... if it's grooved asphalt, where there are ruts from use, it's likely to start doing it sooner, like about 90. But even on a perfectly flat smooth road it'll do it at some speed.

It's a 97 SS with C6 wheels on it. The last time I drove it over 140 was some time ago, and it had the stock 17x9's on it then. Point being, it was stable at that speed at that time. Since then though, I've had the K-member out twice and put the C6 wheels on it.

So I had it aligned a couple weeks ago, all is well, at least nothing wildly loose or broken, and while it was a little out of alignment, it wasn't waaaay out or anything. Still same results.

The only part of this suspension that's new to me is the rack. Only rack and pinion vehicle I've ever had. How do I know if that's worn out?

The other wildly speculative guess I have is that with the C6 wheels, the car is about 1/2 *taller* than stock, and it's on the original shocks. Is it getting too much air under it, with nothing to dampen it?

Feenix

Are the tires good? Any deformations like flat spots in a tire rear their heads at higher speeds usually. Severe tire issues you'd feel at any speed and it'd get worse the higher you go.

I had some flat spots after the car sat for awhile but the car felt totally normal until I reached 75+ then I started getting alot of feedback like vibrations, wobbling etc.

350350

I don't think so... definitely no vibrations at all, even when it's wobbling, and no obvious odd wear patterns or anything by visually inspecting the tires anyway. Like I've seen a tire with a slipped belt before, but you can usually see an odd wear pattern. A little thin on tread, but still legal.

CharlzO

Just a silyl question...but have you double-checked the balance on all the tires?

Procharged94Lt1

Another silly question..where are you driving over 110 and 140?

Injuneer

The side-to-side alignment of the rear body over the rear axle is controlled by the panhard rod. Check for worn bushings, loose or damaged bar.

350350

You know, I didn't even consider that the rear end might be the problem... with the 10" wheels on the back, it's very obvious just standing behind the car that the rear end is NOT centered perfectly under the body. I'll get under it tomorrow and check it out!

jmd

In the front, wheels that put tire tread further out gives the tread further mechanical leverage over the suspension.

Wider tread will follow ruts more.

The stock alignment isn't likely to work well with your C6 setup.

Generically speaking, more toe-in keeps a straight line better and more toe-out helps turn-in for corners. Your car might benefit from a little more toe-in.

Caster changes the steering angle on which the spindle pivots. Some added negative might help your setup.

Camber shouldn't be a primary issue for the instability of the car. The rear probably isn't either.

I don't know the 4th gen alignment and I find it a real hassle to find a shoppe that will work with anything outside of stock without completely giving me doubletalk, lies and showing incompetency. So good luck and hopefully you can find others running bigger treads who have some ideas on alignment specs.

350350

Well, first I did crawl under it just quickly today and I don't see anything obviously damaged or missing under the rear suspension. However, I did see that the *inside edge* of the *driver's side* tire is worn to the cords while the rest of the tire is fine. (And by fine I mean 5/32"-ish... not bald, not awesome) Best guess is that it slipped a belt and is wearing oddly on that inside. Both rear tires have always been rear tires, so it's odd that it's worn like that.

But also I posted this link in the 'C6 wheels on a 4th gen' thread to see if anyone else had issues with alignment. Way back in the old days I put 16x8" Corvette wheels on a lowered 78 Malibu and had all sorts of issues until I finally found a shop that would align it 'not stock'...

punkslapper

+1 I too had the wooble I replaced the panhard and while I was at it the rear lower control arms, and hot dam what a difference it made. Gone is the wooble feels nice and firm on take off . Heck I even lost most of those pesky rattles and squeaks.

350350

OK so I learned a couple of things... punkslapper, do you mean you replaced your stock bushings, or you replaced the panhard and control arms with aftermarket units?

First of all, recall that I had it aligned recently and the alignment guy said the front end all 'looked good'. Well, I got it up in the air today and looked it over carefully, and the passenger side tie rod end is so loose that simply grabbing it with my hand made it 'clunk' and I can literally rattle the rod end. That wheel be floppin. So much for the alignment guy having a clue. In fact, I don't know how he managed to get it aligned.

Secondly though, while there is nothing obviously broken in the *rear*, nor are any of the bushings completely disintegrated in the control arms or panhard rod, I was amazed at how soft all those items are. I can move them around by hand. I can twist the control arms, and the panhard rod flexes of course if I grab it in the center. As stock pieces, these had to be absolute crap even when new. I don't see any point in putting stock bushings back in them. I'll save my pennies for aftermarket units.

*sigh* I foresee it up on blocks for the winter after the first snow.

Dear Santa:

punkslapper

yes I replaced them with aftermarket units from Founders Performance they are very cheap on Ebay.They have poly bushings and grease fittings, they are very well built and priced right.But like I said they made a world of difference for my wobble .But know I can hear all the work I need on the front end. heres the site www.foundersperformance.com. I would definatly remedy that tie rod issue I promise its no fun when they break or come loose

350350

Dayum, that's some reasonable pricing... I know I want the adjustable panhard rod, but if I'm going to lower the rear an inch do I need the adjustable control arms too? I can't remember the 'fix' for the change to the geometry...

punkslapper

You might or maybe even the relocation brackets I am not sure. I just went the non adjustable.Hopefully somebody will chime and give us both the answer. I have tossed around lowering mine too.

350350

Yeah I'm kinda lowering and I'm kinda not. The 18/19" Corvette wheels are an inch taller than the stock wheels, so 1/2" of ground clearance. So, lowering the car 1" only drops the ground clearance to 1/2" lower than stock ride height, while still dropping the axle centerlines an entire 1".

Anyone?