Reiver

and it drives me nuts. '83 SC.
Have new tie rods, ball joints, and shocks and no slack or wheel wobble with the front end up checking the bearings ( no noise either)...and I've readjusted them for the hell of it.

Ay 73, or so, mph I get a very slight shimmy...below that nothing.
I've had the wheels balanced twice.

All I can figure (relatively new set of tires) is a bad tire...

Can bearings exhibit that kind of issue even tho they have no 'play' or noise?
That's the only thing I've not changed out.

Steering is very tight and responsive and no play in the steering wheel column.

Amber Gramps

Wheels can balance out perfectly on the machine and still have bad harmonics at various speeds. I believe the balance machines spin at about 55 miles per hour, so traveling at a speed above that will throw off the balance.

You may need to break the bead, spin the tire a quarter turn from its current point on the wheel and start over.

I have even had to remove the tires from the rims and swap them side to side, keeping them spinning the same direction, but wearing the opposite side. Our negative camber causes more ware on the inner tread.

Any chance your yellow or red dot wasn't lined up with the valve stem? The dots show the lightest point on the tire. If your tire s ores a red dot, you definitely want it at the valve stem.

Reiver

Amps I suspect you are correct on that....I'll check my dots....

race911

Simplest thing would be to just swap the wheels back-to-front. Yes, it would look funny. But you're just going to go a few miles up the road and back.

Reiver

That's a damn good idea...I've had sports cars for 50 plus years and never had this issue.
Dumb luck but that's why it's been giving me fits, been trying to fix the unfixable.
I'll do the swap and try that out.

The Brewmeister

There could be a runout issue with one of the tires. What brand and spec (speed rating) tire are you running?

Reiver

They are Firestones Y rated.

cal44

I had that same issue on a '84 911. They balanced the tires three times before it got straighten out.
The prior owner had purchased a lesser brand tire. I should have put on Michelins and would have been the last of it.................

Derek911

How about moving further up the chain. Steering rack, bushings right up to the steering wheel. There are threads with steering shimmy caused by worn or loose steering components.

Reiver

Steering is tight and spot on...no wobble in the wheel bushing either...that's all good.
I suspect the Firestones have an issue.
The shimmy is very slight, feel it not so much see it in the wheel....as Lamps said I thin it is a harmonic from a cheaper tire, or one that was poorly made....I'll be working there I think, prob is they are pretty new with little wear.

MUSSBERGER

Flat spot?

ron mcatee

Do you have a friend with the same size tires/wheels? Swap and see what that does.

Reiver

Good idea, race911 suggested I swap rears to front and was contemplating that but have 225/50 16's on the rear and don't think that would be a fit up front on the SC.
There is not another 911 in my small town btw.

race911

Ran 225's on all my cars over the decades.

Again, look at it this way--you're just going to leave your driveway, through the neighborhood, and out to the highway for a few miles. All you're trying to do is take a variable out.

Reiver

I'll try it then...doesn't bother me to drive it like that btw....I'm only 1/2 mile from a 65 mph State rd.

As to the flat spot suggestion...only if it came that way, I drive it too much for it to develop one from sitting still, 12k or more a year.