Racingswh

I am at Pocono right now and we are using the North course infield and the Main oval counter clockwise same as NASCAR. The car is stock. I am on Sport Cups 345/30/19. As I accelerate off of 1 or onto the front straight as I approach 120 mph under acceleration to 140 mph the car starts to wave or wobble from side to side oscillating back and forth and when I breath out of it it then settles down. It's a very uncomfortable feeling and honestly I have never felt anything like it before in any other car. Suspension is stock. Nannies are completely off. I just had it aligned yesterday. I have checked all suspension bolts and they are tight. Could it be bushings movement? O's something in the driveline out of alignment or balance? Does anyone have any thoughts?

Alignment is 2.1 negative camber front. 1.3 negative camber rear. 0 toe front. 7.6 caster both sides front. 1/16 toe in both sides rear.

95jersey

You could have lost a wheel weight on your rim (giving you a tire balance issue). One thing that will cause this is loose lug nuts. The unbalanced tire sound like it to me as it only happens at high speed.

Check to make sure your brake calipers are also mounted tight. and check your tie rods.

crease-guard

Bad or loose wheel bearing?

Jay

Painrace

Go to 1/32" toe out on each side and try it again!

Jim

Racingswh

Changed settings. Negative 2.1 camber front, 1.0 rear. Front toe out 1/32. So just a hair out in front. Toe in rear 3/32 both sides.

So we used the Tri Oval and I drove right out on track from the alignment shop at Kost tire near the track and the guys there took me right away and were awesome!! We checked everything we could think of. Tie rods, wheel bearings, bushings, hubs, etc and came up empty. The sport cups had pulled it out of alignment a little so we set it back to tue above specs. When I am at higher speeds and accelerating the car predominantly in 4th gear the car starts this side to side wobble which was noticeable to following cars and extremely noticeable to passengers who wanted to experience it as well. I then put the car in 5th and gently accelerated up to 150 mph and no significant wobble. Put it back in fourth to pass slower cars and roll into it the wobble comes right back.

Seems to me like it's driveline related. Maybe differential related? Biasing back and forth from one rear tire to the other? Is that possible?

Sidney004

Could be a tire; if you could swap some wheels and tires from another Z06 and run a session, that could rule that out.

Supercharged111

I got that death wobble in a Celica GT4 in Japan, thought at 60-80kph and more severe. The rear was massively toed in. 4th gear applies more torque than 5th, do you maybe have a bushing torn up out back that allows the wheels to toe in? It's odd that you don't feel it in the lower gears if this were the case.

brkntrxn

What you are describing is not a rare occurrence with Mustang Cobras with an IRS. In my experience with my 99 Cobra, the root cause is usually traced to the following:

- bad alignment (you have eliminated this)
- loose half shaft nut (not sure if you checked this or not)
- bad wheel bearing
- bad shock

-kevin

Racingswh

I will check the halfshafts but we were also thinking a bad shock as well. The bushings while stock and rubber really look just fine. None are pushed out and they are in good shape.

I am actually taking my friend who owns the local Chevrolet dealership for a ride on track this afternoon. We are going to try and get it fixed under warranty.

Bill Dearborn

If the car felt fine at 150 in 5th gear and felt good in 5th getting to 150 you have eliminated the following: Wheel bearings, rear axle shafts, differential, shocks, springs, tires, wheels and anything else that rotates at the same velocity at a certain speed no matter what gear you are in.

That leaves you the engine, torque tube and the transmission.

Bill

AU N EGL

on a banked track????

Bank tracks seems like they might be fun, but need to have the alignment changed before driving the banks to:

-1.0* left and 0.0* right front ( counter clockwise driven ) or there about depending on the banking degrees

0.0* rear both sides.

brkntrxn

Bill,

I respectfully disagree that just because it does not do it in 5th then the issue is something else. There isn't enough acceleration in 5th to force the issue to show itself. And te reason it is not felt in 1st, 2nd, and 3rd is because you blow through the speed range so fast. This situation occurred on my Cobra more than once and it would only show up in 4th.

Kevin

ghoffman

Lousy stock shocks?

Racingswh

Definitely some crazy sensations going on. Hard shift into 4th starts the wobble immediately. Ease into 4th and then to the floor accelerating past 130 and the wobble starts. Breathe out of it stops the problem and back to the floor gently in 4th no wobble all the way to 6500 in 4th which looked like an indicated 151 and then into 5th no real wobble.

We are thinking shocks or bushings or a bit of both.

The good news was the ACR worked great. Saw 170 mph on the front straight which was fun. So it's not a lost weekend at all. The weather is awesome and it's just great to be here with everyone. So far a great time!

SouthernSon

Generally true but the acceleration factor is loading the rear and unloading the front (although not to a great deal at 140mph unless 1000HP) so, perhaps, the suspension components could be affected if out of spec.

Racingswh

So I am back. This morning we weren't running the long course so none of the high speeds for extended periods but we did use the North course which allows me to get it into the 130's without any problem. I take my friend who owns the local dealership for a ride so he can try and explain it to his service guys. First session of the morning tires are cold second lap in. I know I have to make sure he sees it first hand because the warm up lap was fairly uneventful. I am rolling through the bowl down towards turn one at about 100 mph and I mash the throttle in 4th. The car wobbles left as it picks up speed, wobbles right and then back left again to require some opposite lock to stop the slide at about 120 mph with the Pocono wall immediately to our left and coming up quick. I gather it up and he screams screams "Your effin crazy, how the h___ do you drive this thing?" I bust out laughing all the way back to the paddock. As I am going around letting it cool down I ask him if he needs to feel it again and start laughing even harder!!

Now it's starting to do it in third gear as well even loaded up in the corners under hard acceleration. Breathe out of it and it stops.

Bruce is going to do some research and it will stay at his dealership until they figure it out and fix it.

My next question is if they can't find the issue do I go down the long slippery slope of changing and modifying everything on this car to fix the problem and voiding any and all warranties or do I sell this one and buy another car specifically a Z06? How fast can a GS be? Will it be as quick as a well driven STO car? I myself doubt it.


Thank you very much for all the replies. We will chase all possibilities and really appreciate all the advice given!!

1stz51

Had the same problem at Roebling... Ended up being being a left rear balljoint

larryfs

I've seen that on a C5. Never knew the cause.

2 GTOs

That is a good friend to have. If he needs a new customer, and another friend, please PM me details. Always nice to have a dealer that is fair and does not immediately put his hands up because you exceeded 55mph.

JimbeauZ06

I had a chance to experience this first hand and thought you were just exagerating because the car was too slow and you really didn't like it in the first place. Thought it might have had something to do with the two really fast STO Z06s running around out there.

I'm really curious what this ends up to be. I hope Bruce can figure it out even though I know you're going to sell it and get a Z06 because it's just too damn slow.

I've been in a number of different Corvettes and other cars and I've never felt anything like this before. We talked through it with several other experienced Corvette drivers and a couple of pretty good mechanics, ruled out the obvious and still couldn't figure it out.

Wobble is an understatement. This was a big side to side motion and even at lower speeds coming out of the North Course onto the bowl when the throttle was applied during passing the car moved side to side violently. It really did not feel like a suspension issue. Felt like drive train, like the rear wheels were receiving alternating applications of torque (I do realize suspension issue could have that effect) but after everything you did to rule those issues out, just couldn't make sense of it.

Keep us posted!