Help with tracking down a mild steering wheel shimmy?

1950StangJump$

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2008 GT. Been unable to be rid myself of a slight highway steering wheel shake for years. Doesn't really manifest itself until 50+ MPH, and it doesn't go away as speed climbs. IT IS ROAD DEPENDENT, i.e. glass-smooth roads produce virtually no shake in the steering wheel, while bumpy roads seem to make it considerably worse. At times, I have rationalized that it was nothing more than increased vibration from the lowered suspension and low profile tires but, in the end, I don't think its "normal." I have noticed no bump steer issues.

Here's the changes as succinctly as possible. Most of the changes were not specifically to address the shimmy, but lots has been done:

  • Purchased the car 2+ years ago. Stock suspension but 20" rims. Found one of the rims bent, so I replaced all rims (with new 20" Foose rims) and and installed new Nitto tires. Everything roadforce balanced then (and multiple times over the past two years), but the shimmy didn't change.
  • About 18 months ago, installed Pedders adjustable coilovers to lower the car. At the same time, I installed camber bolts and a BMR adjustable front sway bar. Car aligned within specs. No change in the shimmy.
  • A year ago, I decided to build up the motor. In the process, I found the A-arm bushings were bad, so I replaced both A-arms with the upgraded GT500 A-arms. I thought I might have stumbled upon the true shimmy problem, but it had no effect when replaced and car aligned.
  • With the new motor installed, I put in a BMR lowered K-member, radiator support, cross brace, etc. Car aligned within specs. All tires roadforce balanced again. Still no change.
So, as you can see, most of the front suspension, wheels, and tires, have been replaced over the years, with no real change to the shimmy. At this point, I'm down to the steering rack and tie rods, and those can be changed out for $300 in parts (plus alignment). But, I do have a car lift, and with the car up, I can get ZERO play in the rack or tie rods when I grab and tug on them, so it feels like replacing them would be a shot in the dark.

I'm at a loss.
 

stkjock

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if you have a square set up have you rotated the tires to see if it changed at all?

I realize you said new tires/wheels + roadforce... but it's a simple test
 

1950StangJump$

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if you have a square set up have you rotated the tires to see if it changed at all?

I realize you said new tires/wheels + roadforce... but it's a simple test

Thanks for the input . . . but it's a staggered setup . . . 235/35/20 on the front, 295/35/30 on the rear
 

1950StangJump$

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Good thought! I should have mentioned that I explore that possibility also, but they are the correct bore size
 

Laga

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Just throwing out ideas here. Since it is road and speed sensitive, check center hanger on driveshaft. It could be worn out and causing a vibration. Also, how are your front brakes? See if a caliper is not releasing or a rotor is warped. Then check for play in front wheel bearings.
 

1950StangJump$

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Just throwing out ideas here. Since it is road and speed sensitive, check center hanger on driveshaft. It could be worn out and causing a vibration. Also, how are your front brakes? See if a caliper is not releasing or a rotor is warped. Then check for play in front wheel bearings.

Thanks for the ideas.

In the last two years, I have also put in a Magnum XL and one piece driveshaft. Both have been out a couple times over the course of the build. No difference.

Have also put in new brakes, Brembo style calipers, and rotors .... no change. Also, no change in the shimmy when I hit the brakes, like you'd expect is the rotor was warped and dragging.

but ... I haven't not the wheel bearings. What's a good way to check them? They make no noise, if they matters, and I can get no wobble by grabbing the wheel and shaking when on the lift
 

MrBhp

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I chased a shimmy in mine. Turned out to be a tie rod end.
 

Laga

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Thanks for the ideas.



but ... I haven't not the wheel bearings. What's a good way to check them? They make no noise, if they matters, and I can get no wobble by grabbing the wheel and shaking when on the lift
Not the wheel bearings then.
 

OX1

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What correction was required during roadforce? If a lot, maybe the tires were just not round.
Would be odd two sets of tires had this, but I've had many new tires not round in the past 8 years.

Way more than you think there would have been. I was allowed to work OT as much as I wanted for 9 straight years. I went crazy with multiple sets of tires for almost every car I own (IE, mustang had winter, summer, drag, and road course sets), which is the reason I had so much experience with out of round new tires (plus I have my own machines, so it's kind of easy to spot spinning on balancer, especially when it wants a bunch of weight with news tires).
 

1950StangJump$

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What correction was required during roadforce? If a lot, maybe the tires were just not round.
Would be odd two sets of tires had this, but I've had many new tires not round in the past 8 years.

Way more than you think there would have been. I was allowed to work OT as much as I wanted for 9 straight years. I went crazy with multiple sets of tires for almost every car I own (IE, mustang had winter, summer, drag, and road course sets), which is the reason I had so much experience with out of round new tires (plus I have my own machines, so it's kind of easy to spot spinning on balancer, especially when it wants a bunch of weight with news tires).

Thanks for the input.

The front has 235/35/20 Nitto 555 G2.

I don't remember how they road balanced the first couple times. This last time, they showed in the low 20s (not sure the unit of measurement?), which I know is not ideal, but I was told it wouldn't cause vibration. Ideal is less than 15?

The machine told them they only stood to lower the number by 1, so they let it be and just ensured the balance of correct. Thoughts?
 

Sterling

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Could be a tooth broken in your rack and pinion. Have you ever had the steering shaft out? You could have put the bolt in backwards when you reconnected it. I'm talking about the bolt that locks the steering shaft into the rack and pinion. On one side there are threads, on the other side there are not. If you put the bolt in backwards the bolt really doesn't tighten anything. Easy thing to overlook.
 

1950StangJump$

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The bolt for the shaft has been out several times, but it is definitely in the correct way . . . yea, the bad rack-and-pinion is as good a theory as any. Sure hate to just drop the $ for a new one when I don't know the old is bad, but I'm sick of this shit . . .
 

Sterling

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The bolt for the shaft has been out several times, but it is definitely in the correct way . . . yea, the bad rack-and-pinion is as good a theory as any. Sure hate to just drop the $ for a new one when I don't know the old is bad, but I'm sick of this shit . . .
LOL. You're telling me. Working on my car has always been difficult and frustrating. I had sort of the same issue as you and did the EPAS swap from a 2014.
 

DieHarder

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By chance do you have star washers holding your rotors on? On original wheels they often put on one or two on the studs to hold the rotor. I had them on mine and didn't realize when I changed wheels that they were now interfering with the back of the wheel sitting flush to the rotor. Couldn't get rid of the shimmy no matter what I tried. Finally put the front up on jacks and checked the run out. When I pulled the wheel the old star washers were still on. Removed them and never had a problem since.

Couple of other possibilities: 1) Out of balance rotors. 2) Tie rod/bushing and tie rod end. Just had mine replaced when the shop found they couldn't align the car properly. Since yours aligns okay I would look at the other issues first. 3) Bad rims. Unfortunately, my experience with wheels hasn't been ideal. I've purchased at least three sets that were out of round. One set I had repaired so they're serviceable. The other I just sent back and the third were brand new out of the box. The entire face of all of them were offset from center about an 1/8". Can't make this stuff up. Moral of the story. Avoid cheap aftermarket wheels.
 

1950StangJump$

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By chance do you have star washers holding your rotors on? On original wheels they often put on one or two on the studs to hold the rotor. I had them on mine and didn't realize when I changed wheels that they were now interfering with the back of the wheel sitting flush to the rotor. Couldn't get rid of the shimmy no matter what I tried. Finally put the front up on jacks and checked the run out. When I pulled the wheel the old star washers were still on. Removed them and never had a problem since.

Couple of other possibilities: 1) Out of balance rotors. 2) Tie rod/bushing and tie rod end. Just had mine replaced when the shop found they couldn't align the car properly. Since yours aligns okay I would look at the other issues first. 3) Bad rims. Unfortunately, my experience with wheels hasn't been ideal. I've purchased at least three sets that were out of round. One set I had repaired so they're serviceable. The other I just sent back and the third were brand new out of the box. The entire face of all of them were offset from center about an 1/8". Can't make this stuff up. Moral of the story. Avoid cheap aftermarket wheels.

Great thoughts, thanks. The star washers are gone, and the rotors have been changed three times over the years (for different reasons) with no change in the shimmy.

The Chip Foose rims were brand new. I realize that doesn't necessarily mean they are absolutely true. But, not one of the 3 times I had the tires rebalanced did anyone mention they observed anything .... which I also recognize is not an absolute guarantee.
 

msvela448

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If you can... Temporarily (like for an hour) borrow a set of wheels and tires from another friendly Stang owner and see if the problem goes away... If it does then it's your wheels and / or tires. If the problem persists with a different set of wheels and tires then it's something in your steering or suspension.

Sent from my SM-N975U using Tapatalk
 

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