308 steering shimmy

What about the various splined "squeeze" connections, u-joints, telescopic joint, etc. in the path from the steering wheel to the rack input pinion shaft -- all OK and tight? Seems you checked most everything else.

 

Shimmy in normal use is ONLY caused by either of 2 things.

1 wheel/brake disc balance
2 tyre/wheel not round.

Loose wheel bearings, worn shocks, alignment etc will not cause it.

Under braking, shimmy can be caused by warped brakes, but this will go again when you get off the brakes. A warped disc could vibrate while off the brakes, but only at very very high road speeds. Way over 100 mph.

 

Check #2 particularly. I've been chasing a vibration above 80 MPH for a while, and just recently tracked it to the front passenger wheel being out of round. It balanced, but it's physically just a bit ovoid and will have to be replaced.

 

Check the tyres for ply seps.

 

The passenger side bush on the end of the steering rack is known to develop play, so passenger side 3o/c-9 o/c. Maybe this would encourage or allow a wheel vibration.

The bush costs 40$ and can be replaced with some effort and skin loss.

 

Not even the slack bush will cause it. The shimmy is the result of transmitted vibration.

But, yes, the bush should be kept in good condition as a matter of course, but it won't cause or exaggerate the shimmy.

 

Sometimes tires just go bad, without looking bad.
If they are balanced and the alignment is good, try new front tires.

 

You might check to see what kind of balance the shop gave you. I had the same problem and it turned out to be I had the wrong kind of balance done. The weights are now on the outside vs the inside of the wheel. The NTB that did it explained the different types of balance but I can not remember the details.

 

When I used to use Pirelli's, they had a nasty habit of rotating slightly on the wheel and causing a vibration at 90mph. Not below or above. Cheap and easy recommendation....have them rebalanced again. Before driving, draw a line from the wheel onto the tire. 1/4 " rotation was enough to cause the vibration. Solution? Have the shop use less soapy water when mounting. Drive easy for the first 100 miles or so.

This problem was eliminated when I went to Continental Extreme Contacts. They must fit tighter on the wheel.

Hope this helps.

Tom

 

Try wheels/tires from a buddy's car that doesn't have the problem. you can do one at a time or all at once. one at a time takes longer but you can pinpoint it down to one wheel/tire combo.
hth,
chris

 

If the general opinion is that it's the tyres, then you could swap front to back and it should go away....