I get the same shimmy on my F15. It usually happens immediately after bounding out of a moderate pothole, of which we have MANY around my area. Have not had a chance to crack open the steering box yet, just learnt to tolerate the problem for now. I find the shimmy worsens quickly if I don't make a correction immediately. If a little steering force is applied L or R, then the wobble can be stopped in it's tracks. The first time it happened, I nearly pooped myself, because it was VERY violent. I hadn't learnt how to stop it at that stage, and because it was an isolated country road, I went for the brakes! It sure stopped the wobbles, because the truck literally came to a screeching halt. The silver lining was that I discovered the braking system is extremely good.
Curiously, I have not had this problem at a reasonable speed! In fact, once I go over 40-50km/h I can relax. Perhaps centrifugal force stops the problem occuring at higher speeds?!?! I do know the springs are good, so they shouldn't be an issue. Can't speak for the steering linkages, except they have no play which can be induced, or which is observable with movements of steering wheel back and forth. In fact even minor movements result in that movement being visible right through to the wheels. Can't feel any play in steering box at all, so the almost continual but very minor corrections needed to keep on course has me intrigued. For now, I am trying to resist the urge to disassemble the steering box, because I know it will become a full rebuild that I can't really spare the cash for just yet. Besides, I wouldn't be able to enjoy the challenge of driving a CMP.
The tyres I have on, are almost new. They are, however, Indian imports. If left sitting for some time (>1-2 days), they develop a flat spot that takes a couple of km driving to disappear. Once tyres are warmed up, they are fine. I think they have a bit of road noise, but can not really tell. The diesel engine is too noisy for me to be certain.
In near future I will be swapping the current tyres for a set of new NDBT ones. I will be curious to see if that change makes much, if any, difference to the wobbles. I will get the new ensemble professionally balanced before they are put into service. The current tyres/wheels had been balanced too, so I assume that isn't contributing (how's that for optomism!).
I am following this thread very closely. While certainly no comfort to know others are suffering same scenario, the suggestions are very, very, valuable to me, and if the tyre change doesn't fix the issue, the suggestions will assist me to know where to look next.
Thanks, to all contributors here
