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Discussion Starter · #1 · (Edited)
Cayman S, GT3 LCA's, PSS9 just rebuilt, corner weighted and aligned.

Hey Guys. Not sure if this is the right section but looking for input to the Troubleshooting of a shimmy or vibration that occurs when taking sharp right at decent speeds >30km/h (loads up on left). Intermittently, a judder is felt on the left Front is felt through the steering wheel. I haven't been able to record this.

Separate to this, I found that I get this judder shake when turning the steering side to side on the spot.
eg.
https://www.youtube.com/watch?v=NIovd9o8bJU


While separate scenarios, the common factor is that vibration only occurs on the left front so I'm starting to think these 2 symptoms are related. It is triggered by the grip in the tire. I believe I can reproduce the judder when turning right on loose road surface like gravel (hard to find but like a round-about).

So far, 2 shops have said there is no play. I did have the inner tie rods replaced a 2yrs ago and drop links recently replaced.

Notes:
- It's only happening on the left side too.
- No noise or issues going straight
- I do get slight shimmies when turning a 90 degree corner at speed 30-60km/h. Slip angle of front tire seems to be a required parameter.
- Don't feel any issue on long sweeping corners. If I'm being picky, sometimes I feel a strange wobble on the left tire, like a tremor.

It could be the tire but then I think the suspension should be able to absorb any vibration instead of transferring it through the steering quite dramatically. I've read about ackerman effect but believe this shouldn't happen to this level.

What else can I check. Wanted to your experiences before I go for around of diagnostics or determine if I will go with a proactive remediation plan such as refresh components anyway. Also Happy to hear any recommendations on components I should consider refreshing at 93k kms!
 

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Cayman S, GT3 LCA's, PSS9 just rebuilt, corner weighted and aligned.

Hey Guys. Not sure if this is the right section but looking for input to the Troubleshooting of a shimmy or vibration that occurs when taking sharp right (loads up on left). Intermittently, a judder is felt on the left Front is felt through the steering wheel. I haven't been able to record this.

Separate to this, I found that I get this judder shake when turning the steering side to side on the spot.
eg.
https://www.youtube.com/watch?v=NIovd9o8bJU


While separate scenarios, the common factor is that vibration only occurs on the left front so I'm starting to think these 2 symptoms are related. It is triggered by the grip in the tire. I believe I can reproduce the judder when turning right on loose road surface like gravel (hard to find).

So far, 2 shops have said there is no play. I did have the inner tie rods replaced a 2yrs ago and drop links recently replaced.

Notes:
- It's only happening on the left side too.
- No noise or issues going straight
- I do get slight shimmies when turning a 90 degree corner. Slip angle of front tire seems to be a required parameter.
- Don't feel any issue on long sweeping corners. If I'm being picky, sometimes I feel a strange wobble on the left tire, like a tremor.

It could be the tire but then I think the suspension should be able to absorb any vibration instead of transferring it through the steering quite dramatically. I've read about ackerman effect but believe this shouldn't happen to this level.

What else can I check. Wanted to your experiences before I go for around of diagnostics or determine if I will go with a proactive remediation plan such as refresh components anyway. Also Happy to hear any recommendations on components I should consider refreshing at 93k kms!
Its been a long long time, but I think I had this like 6 years ago with a set of pss9's. If memory serves I pulled the coilover back off, and there was an issue with the camber plates / pillowball mounts. Something was binding (I think I had assembled the mounts and coilovers incorrectly.)

The other thing I've run into during the sway bar install process was having to loosen the rack a little. I forgot to retrq the two bolts holding it, and it cured a an issue with the steering. Again also 5 or 6 years ago.

I'd check the offending coilover and the rack (if you were doing something with your sway bar.) Again though - sorry this is from memory many years ago.....
 

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Discussion Starter · #3 ·
Its been a long long time, but I think I had this like 6 years ago with a set of pss9's. If memory serves I pulled the coilover back off, and there was an issue with the camber plates / pillowball mounts. Something was binding (I think I had assembled the mounts and coilovers incorrectly.)

The other thing I've run into during the sway bar install process was having to loosen the rack a little. I forgot to retrq the two bolts holding it, and it cured a an issue with the steering. Again also 5 or 6 years ago.

I'd check the offending coilover and the rack (if you were doing something with your sway bar.) Again though - sorry this is from memory many years ago.....
Thanks G.T! No worries if you can't remember the details! I'm still learning about what components could come into play so any inputs are appreciated! Leaves me with a few avenues to explore :)
 

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PCA Nat'l DE Instructor
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You could swap tires front tires from one side to the other, to see whether or not the issue moves with the tires. A simple check, to help isolate one variable...

Sent from my XT1650 using Tapatalk
 

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Discussion Starter · #5 ·
You could swap tires front tires from one side to the other, to see whether or not the issue moves with the tires. A simple check, to help isolate one variable...

Sent from my XT1650 using Tapatalk
Thanks mate.

Summary of things to look into, including the things I've already done. Will re-order later.


Possible causes
- Play in Inner or outer tie rods
- drop links
- Sub frame
- Tires (tire swap)
- Power steering (fluid?)
- Play in Ball joints
- play in spherical bearings
 

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Thanks mate.

Summary of things to look into, including the things I've already done. Will re-order later.


Possible causes
- Play in Inner or outer tie rods
- drop links
- Sub frame
- Tires (tire swap)
- Power steering (fluid?)
- Play in Ball joints
- play in spherical bearings
This sounds and looks like the Ackerman effect to me and it's quite common and normal on sports cars. Certain tire brands and lower temps can also cause it to be more noticeable for some vs. others. Sports cars are not set up with the same steering geometry as regular cars to help prevent this issue due to performance reasons, so there are some compromises and this low speed wheel hop can be one of them. A Toyotas steering is not optimized for a race track any more than a Porsche is optimized slow speed turns a parking garage.

The result is when moving slowly with the wheel at or near full lock such as in parking garage, one wheel is taking a different arc than the other is, so what you hear and feel is one of the tires being pushed and "skipping" across the floor. As stated, this might get worse in the winter when the tire is colder.

There are a dozens of threads just like this for the same symptoms in multiple sports car forums, but the good news is there is likely nothing at all wrong with your car. http://www.planet-9.com/981-chat/136297-low-speed-wheel-hop-ackermann-effect.html
 

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Discussion Starter · #7 ·
This sounds and looks like the Ackerman effect to me and it's quite common and normal on sports cars. Certain tire brands and lower temps can also cause it to be more noticeable for some vs. others. Sports cars are not set up with the same steering geometry as regular cars to help prevent this issue due to performance reasons, so there are some compromises and this low speed wheel hop can be one of them. A Toyotas steering is not optimized for a race track any more than a Porsche is optimized slow speed turns a parking garage.

The result is when moving slowly with the wheel at or near full lock such as in parking garage, one wheel is taking a different arc than the other is, so what you hear and feel is one of the tires being pushed and "skipping" across the floor. As stated, this might get worse in the winter when the tire is colder.

There are a dozens of threads just like this for the same symptoms in multiple sports car forums, but the good news is there is likely nothing at all wrong with your car. http://www.planet-9.com/981-chat/136297-low-speed-wheel-hop-ackermann-effect.html
Thanks ICNU! I've read about the ackerman and will stay open to it as there is a high probability, I'm experience a mix of symptoms. I'm still suspecting there's something else at play because I only get the vibration on the left. There are scenarios where I get a subset of this shudder during sharp corners and it needs 30+ km/h to induce it (something I haven't been able to capture on video)

It's getting under my skin when the car shudders in a corner, it's like a metal knocking effect, which I think shouldn't be so pronounced.

I remember this one time, when I drove around this "round about" which was under road works with a loose gravel surface, I would experience what I perceive as the same juddering as the youtube video. Is it the same? not sure but I think it should not be happening to this extent. I thought this would eliminate the correlation with "the sticky tire/surface trigger". I wish I had gone around it a few times to make sure it was reproducible but it was manned by road workers :)

Feel like I'm chasing a ghost and it's going to cost me. Diagnosis continues!
 

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Yes, if you are experiencing this during normal driving, then it's likely something else. The Ackerman effect typically shows itself in very slow moving tight places where near full lock steering in any direction is used such as moving in or out of a parking space in a garage. I've never experienced this driving the car under normal circumstances such as in roundabout with normal steering at higher speeds
 
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