one speed shimmy
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Senior User
Joined: Dec 2005
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From: Longwood, fl
one speed shimmy
Have a 55 F100 with new wheels and tires, balanced twice. New 3" drop axle, shocks, tie-rod ends, inner and outer wheel bearings , new king pins. Just had the drive shaft balanced and new u-joints. At 50 to 55 mph I get a shimmy that is driving me crazy. Old tires new tires it doesn't matter, have rotated the tires, did the same with the old tires and wheels. Only at that speed is when it occurs otherwise nice and smooth. I don't know what else to look at. ???
Lead Driver
Joined: Apr 2002
Posts: 8,813
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From: Littleton, New Hampshire
I assume you've had the front end re-aligned with all those new parts. Toe-in or caster is about all that's left. The last time I had a problem like that with a straight axle a toe-in adjustment fixed it. By shimmy, I assume you mean a vibration in the steering wheel. If it's some other kind of vibration the pinion angle could be off. Other than that I'm stumped... 
Roast em' if you got 'em
Joined: Mar 2005
Posts: 21,989
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From: Rio Rancho, NM
If the shimmy is felt in the steering wheel I'd make sure of the alignment settings, especially the toe-in. It could be a very slight version of the dreaded "death wobble"
The toe-in is easy enough to check in your own driveway. Measure from the front of one tire across the truck to the other tire, note the measurement, repeat the process across the rear of the tires, subtract rear from front and thats your toe-in measurement.
Bobby
The toe-in is easy enough to check in your own driveway. Measure from the front of one tire across the truck to the other tire, note the measurement, repeat the process across the rear of the tires, subtract rear from front and thats your toe-in measurement.
Bobby
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Senior User
Joined: Dec 2005
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From: Longwood, fl
Have an appt saturday morning to go over the alignment again. Haven't tried putting it in nuetral when the shimmy occurs but you feel it thru the entire vehicle not just the steering wheel. Am running drums all around and adjust evenly so don't think I have a warped drum. Will see what happens Saturday. Thanks guys for the info. Will repost after the next round.
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Fleet Owner
Joined: Jul 2004
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From: NM
Ask the tech what specs he's using for toe-in (that's all he can adjust without major work). If he is using the old (stock) spec for a '55, that is for bias-ply tires, and I'm sure you're running radials. Radials need less toe-in, ask him to look up some solid-axle specs from more modern trucks that would have come with radials, or to just set it to a real small amount of toe-in, like 1/16" total.
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Lead Driver
Joined: Apr 2002
Posts: 8,813
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From: Littleton, New Hampshire
Originally Posted by joe hoffman
Have an appt saturday morning to go over the alignment again. Haven't tried putting it in nuetral when the shimmy occurs but you feel it thru the entire vehicle not just the steering wheel. Am running drums all around and adjust evenly so don't think I have a warped drum. Will see what happens Saturday. Thanks guys for the info. Will repost after the next round.
Fleet Mechanic
Joined: May 2006
Posts: 1,696
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From: S.W. Florida
Ok, Ok. Another wild shot in the dark. You said you have new U-joints. I once had a severe vibe at a certain speed after changing u-joints because I had failed too tighten the bolts at the joints enough and the nut backed off to where I had daylight tween the u-joint and the yoke, allowing play there. (rear u-joint) No worries after tightening. Pinion angle very likely as well, like these knowledgeable gents have said. Good Luck!
Postmaster
Joined: Apr 2004
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From: Santa Clarita
Joe, I checked with my front end guru friend and he said the pinion has something to do with it, but usually starts to vibrate or what you call shimmy at the certain speed and continues vibrating past that speed. He said to check the transmission mount for loseness. Sometimes they come loose and can act like the driveshaft being out of line. I know my front alignment is so far out and I haven't got a clue what my pinion is? LOL.. And I don't have what you have despite lowering my truck several times, etc. He said to also check the wheel bearings for excess play. That could cause a shimmy effect at a particular speed. Did this happen with the old rims also? or do you recall what you did and when it started doing this?
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Senior User
Joined: Dec 2005
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From: Longwood, fl
Thanks for the responses and great info. I have never checked the pinion angle since I have owned the truck and it has had this problem since day one. I know the 9" rear was added by the po who may or may not have checked the pinion angle either. All other possible causes have been looked over and so far no remedy. Plan to get into it tonight and check the tranny mount, pinion angle which I am sure is off, and what I am reading by the way is to be set at something between two and three degrees to be correct, and recheck the toe will shoot for a 1/16". My local speed shop has 2 and 4 degree shims in stock so will pick those up at lunch and hopefully put this issue to rest.Will report back tomorrow, thanks again guys...
Lead Driver
Joined: Apr 2002
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From: Littleton, New Hampshire
Originally Posted by joe hoffman
Did not check the pinion angles or match the front and rear. But will do so tomorrow night. Would that only happen at a certain speed or at any speed.