Intermittent Shimmy ?? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

BoxMann · 06-11-2019, 07:37 PM

Is that really possible? Just bought of new set of tires. Michelin Pilot Sport A/S 3+. Were balanced on a road force balancer and mounted at a top notch Porsche indy shop Car drives so much nicer. But occasionally I get this very noticeable shimmy at 75 - 85 mph. Most of the time it's not there, but it happens sometimes.

Any thoughts?

maytag · 06-12-2019, 03:27 AM

Loose steering gear?
Bad ball joint?
Bad tie rod?
Bad wheel bearing?

I'd be checking front end parts, is what I'm saying.

The other possibility: does this occur at the same place each time? (I have a specific spot in my commute where the grooves in the paving cause a front end shake)

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BoxMann · 06-12-2019, 07:47 AM

Quote:

Originally Posted by maytag

Loose steering gear?
Bad ball joint?
Bad tie rod?
Bad wheel bearing?

I'd be checking front end parts, is what I'm saying.

The other possibility: does this occur at the same place each time? (I have a specific spot in my commute where the grooves in the paving cause a front end shake)

I understand that those worn parts could cause a shimmy, but why would it happen intermittently? Wouldn't it happen consistently? And the shop (and PPI) inspected all of that and said everything looks good. And the car was aligned very recently. Those problems would have shown up on an alignment.

And it occurs on different roads.

maytag · 06-12-2019, 09:16 AM

Quote:

Originally Posted by BoxMann

I understand that those worn parts could cause a shimmy, but why would it happen intermittently? Wouldn't it happen consistently? And the shop (and PPI) inspected all of that and said everything looks good. And the car was aligned very recently. Those problems would have shown up on an alignment.

And it occurs on different roads.

Intermittent is certainly plausible. As a part wears, particularly parts that affect steering / alignment, they will respond unpredictably to any input which changes the balance of the car: throttle input, braking, steering input, camber in the road, bumps, etc etc. Intermittent is certainly plausible.

And to your comment below:

Quote:

Originally Posted by BoxMann

.....This is a top notch Porsche shop, not Midas Muffler.

I'd wonder how "Top Notch" they can really be, if they sent you on down the road with an "intermittent shimmy" that they can't diagnose?

PaulE · 06-12-2019, 05:59 AM

How was the car before the new tires were installed? If you had the shimmy on the old tires, and everything else checks out, it could be that one of your wheels is bent so slightly that it isn't visible to the naked eye but still results in a shimmy. The places that repair and true wheels use dial indicators to check trueness in both up and down and side to side. I had all 4 of my wheels trued while they were being refinished, and my car is now the smoothest it's ever been. Of course I went to an HPDE a couple of weeks ago and now my tires' treads are coated in race rubber with stones stuck to them, so that all needs to wear off to get the smoothness back!

BoxMann · 06-12-2019, 07:45 AM

Quote:

Originally Posted by PaulE

How was the car before the new tires were installed? If you had the shimmy on the old tires, and everything else checks out, it could be that one of your wheels is bent so slightly that it isn't visible to the naked eye but still results in a shimmy. The places that repair and true wheels use dial indicators to check trueness in both up and down and side to side. I had all 4 of my wheels trued while they were being refinished, and my car is now the smoothest it's ever been. Of course I went to an HPDE a couple of weeks ago and now my tires' treads are coated in race rubber with stones stuck to them, so that all needs to wear off to get the smoothness back!

Wouldn't a Roadforce balancer detect a wheel that's not true? And also, if that were the problem, why would it happen intermittently?

PaulE · 06-12-2019, 10:09 AM

Quote:

Originally Posted by BoxMann

Wouldn't a Roadforce balancer detect a wheel that's not true? And also, if that were the problem, why would it happen intermittently?

I don't know how a road force balancer works, so I can't say. I've had tires road force balanced and been told I had a bent wheel when the bend was clearly visible, but have never been told that a wheel that looked straight and true had slight bends. It's been my experience over 16 years with my Boxster that these cars are very sensitive when it comes to steering wheel shimmy. The amount of gas in the tank, tire pressure, tread pattern and road surface all can make the shimmy intermittent in my experience. When I had all 4 of my wheels trued and refinished the car became the best it's ever been in 80,000 miles of driving it.