[Shawnqa800720]

I have a mystery for the forum to solve. Under full throttle acceleration I am experiencing a strange shimmy /pulling feeling starting around 60MPH through at least 90MPH. It feels like an auto-steering / lane-change correction, but more significant than that. It is pretty dramatic and feels very unsafe. It should not be breaking loose at that speed and the TC lights do not come on to indicate that is what is happening (and it doesn't feel like that - it is more of a pulling than a sliding out).

Car set up is 1SS with the GM lowering and sway bar kit, BMR rear cradle lockout kit, and BMR front sway bar end links. The tires are Dunlop Race Maxx front (295/30R20) and Race Maxx 2 rear (305/30R20) (both Porsche spec for the GT3 RS).

The BMR kit was installed by a shop and the torque to yield bolts were replaced. Everything seems tight.

I have a few guesses, but I'm not going to color your thoughts yet. Who is our resident sleuth?

[rshelar]

Had the same prob on my 15 SS that I bought used. 4-wheel alignment did it.


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[Shawnqa800720]

Originally Posted by rshelar

Had the same prob on my 15 SS that I bought used. 4-wheel alignment did it.


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Strike 1 - car was recently aligned - thanks for bringing it up though!

[Gunkk]

Originally Posted by Shawnqa800720

Strike 1 - car was recently aligned - thanks for bringing it up though!

So.... you modded your car and now it's not working right. Then poo-poo'd the first suggestion which is also the most likely cause of the problem? Let me guess, the shop that did the BMR mods also did the alignment. Might want to try back there first.

In order of probability (high to low):
1. Alignment.
2. Tires.
3. Driver & road surface/conditions.


There are many forum threads on this topic and almost all of them come back to these 3 root causes:
https://www.google.com/search?q=cama...d+acceleration

[MrChrisLS3]

So is it a "shimmy" or is it "pulling". Post is a little confusing.

The above post is pretty accurate in what may be the cause. But there are still some unknowns to play this game.

Is the suspension kit a fresh install?
If not, how many miles on it?
If it was done some time ago, did this just start?
If above is true, can you recall any pot hole, speed bump, curbing events?
Does it shimmy/pull every time regardless of the road you're on?
Does pull to one side or the other under hard braking?
If it's a shimmy, do you feel it more in the steering wheel, or the seat?
If it's a pull, do you seem to have to consistently fight it, or does it stop when you stop accelerating?

Lowering the car will stiffen the suspension and you will get more feedback from it. So if this was the first pull you've done since install, it is possible that you are just feeling more of what happens naturally when accelerate hard. Unless, of course we are talking about a shimmy, a.k.a. wobble, that's always bad.

Also, about the alignment, was the last one done right after the installation, or has another one been done since? When doing an aftermarket suspension like this, many shops recommend bringing it back after 500 miles or so to check the torque and realign.

Regardless, the correct answer to your question is to take it back to the installer with a clear description of what it's doing, and have them check torque on the bolts, and fine tune the alignment. This should just be part of the deal. I know that the shop that does all of our lifts on our trucks and Jeeps for our dealership will call the customer that bought it and tell them to bring it in after 500 miles so they can check everything. I know a lift and lowering are different things, but the principle is the same.

[95 imp]

Just because it was recently aligned doesn't mean it was done right....

[Move'n Up]

Possible cause;
If a "Track" alignment was performed and you are on an imperfect road that is slightly rutted the car will want to hunt. This is common with large front tires and a track alignment at high speed.

[Shawnqa800720]

Originally Posted by MrChrisLS3

So is it a "shimmy" or is it "pulling". Post is a little confusing.

The above post is pretty accurate in what may be the cause. But there are still some unknowns to play this game.

Is the suspension kit a fresh install?
If not, how many miles on it?
If it was done some time ago, did this just start?
If above is true, can you recall any pot hole, speed bump, curbing events?
Does it shimmy/pull every time regardless of the road you're on?
Does pull to one side or the other under hard braking?
If it's a shimmy, do you feel it more in the steering wheel, or the seat?
If it's a pull, do you seem to have to consistently fight it, or does it stop when you stop accelerating?

Lowering the car will stiffen the suspension and you will get more feedback from it. So if this was the first pull you've done since install, it is possible that you are just feeling more of what happens naturally when accelerate hard. Unless, of course we are talking about a shimmy, a.k.a. wobble, that's always bad.

Also, about the alignment, was the last one done right after the installation, or has another one been done since? When doing an aftermarket suspension like this, many shops recommend bringing it back after 500 miles or so to check the torque and realign.

Regardless, the correct answer to your question is to take it back to the installer with a clear description of what it's doing, and have them check torque on the bolts, and fine tune the alignment. This should just be part of the deal. I know that the shop that does all of our lifts on our trucks and Jeeps for our dealership will call the customer that bought it and tell them to bring it in after 500 miles so they can check everything. I know a lift and lowering are different things, but the principle is the same.

It is definitely more of a pull, but it pulls to one side then the other then the other and so on, so it is like a wide sweeping shimmy. But definitely more pull - it feels a lot like a very exaggerated "lane change fix" on cars that have that. It does seem to go away or at least become less noticeable when not accelerating. Someone mentioned "hunting" which described the motion well.
I haven't tried the hard braking, but I don't remember it happening on the track when braking.
The lowering and sway bar kit were done from the "factory" prior to my taking ownership. Currently about 7K miles on the car and upgrades. And no major events. I do not recall it happening earlier, but somewhere around the time I put wider tires on the car at about 3K miles and the BMR upgrades at about 4K. One of the problems here is that I didn't do a lot of hard accelerating before the 3K miles.
The car gets aligned almost every time I switch the tires between my track shoes and my street shoes.
(another poster) It does get the track alignment, but the pull seems to happen on any surface, including a very clear highway.

I have taken it back to the shop, and he went for a ride. Said he hadn't felt anything like it before and asked me to canvas the forums to help with the sleuthing. He is a very good mechanic and does work on other race cars (but admittedly not a ton of 6th Gen Camaros).


My guesses are the tires which are Porsche spec, so spec'd for a car that is almost 500lbs lighter than my car, so likely a thinner sidewall, combined with the new rear end stiffness from the BMR lockout kit exaggerating the feel of the tires squirming with the track alignment on hard acceleration. I find it strange that the squirm doesn't show up until over 60MPH though. That is still messing with me. I've had it up to 131 on a straight at a local track and it felt very "floaty", which was a little disconcerting. If it pulled at 130 like it does at 60-90, I'd likely wreck, so really want to solve this. I'm not going to rule out the alignment, and will have it more fine tuned. Maybe I need to find a race dedicated alignment shop.


Thanks for all the suggestions so far. Hopefully my answers above help to fine tune or narrow down the answers.

[95 imp]

If the alignment is good, it could be ball joints, worn suspension/steering.

That all should of been checked prior to an alignment though...

[Shawnqa800720]

Originally Posted by 95 imp

Just because it was recently aligned doesn't mean it was done right....

So we have several solutions that seem to have been at issue.

The alignment was done recently, but as @95imp noted, that doesn't always mean it'll be done correctly . The toe on the rears was pretty far off, and was adding to the "hunting" noted by another poster.

In addition, these tires (Dunlop Sport Maxx Race and Race 2) are not the best for our cars - they are a Porsche spec so built for a car ~700lbs lighter. When run at normal Camaro inflation pressures, they are a little flimsy (thinner sidewalls). So they need to be run higher (40PSI cold for regular driving and the occasional hard acceleration; 38 front, 37 rear cold for the track due to higher operating temps).

Car feels much better getting the pressures dialed and the toe fixed. I ran at NHMS this weekend, and most of the hunt was gone and the car felt much more stable overall.

Thanks for playing my investigative game.

[Move'n Up]

Great news, glad to hear you got it sorted out.

[Mighty Mouce]

Shimmy shimmy? I couldn't resist.

[MrChrisLS3]

Come to think of it, I had similar issues with my '96 Vette, when put on a rear tire that was a little wider spec for the wheel width. While it looked cool standing still, at speeds it would "hunt" as described. Since the wheel wasn't wide enough, it pinched the tire and reduced the contact patch, not to mention compromising the sidewall. Not proud of that mistake, but putting it out there for anyone thinking of going wider on the tire without going wider on the wheel, don't do it.