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The Hummer Knowledge Base

Possible Causes of a Shimmy:

There are a couple of other things that can cause balance problems. If the tire shifts on the wheel, if the runflat or beadlock shifts ( if you have these in your wheels), and normal tread wear. I was a bit surprised at this, but I should not have been. Since the rubber compound is tires is not 100% uniform, the balance of a tire changes slightly as the tread wears away. This is one reason for periodically re-balancing the tires. Checking the tire/ wheel balance is part of the "A" service (every 3,000 miles).

If you put the truck in N (T-case), and lift one tire with a jack, you should be able to spin it by hand enough to see if there is an out-of-round problem, and probably also be able to tell if the wheel is bent.

I have used a pile of 2x4 scraps and a screw driver as a crude runout gauge - create a stack of scraps and balance the screw driver on the top. Position it close to the edge of the rim or various locations on the tread and see if the gap size changes as you turn the wheel.

The other things to check, as you already know, are: idler, pitman, tie rod ends, and ball joints (including mounting bolts). You should also check to make sure that the control arm (A-arm) mounts are secure, and the holes are not elongated.

Dave B.

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