shimmy at 55 mph

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gbhrps

Well-known member
Joined
Nov 24, 2002
Messages
285
Location
Ontario, Canada
Gentlemen,
Newly frame off restored 55 Tbird with all new suspension parts, has a shimmy at about 55 mph, which is repeating in nature. It quickly vibrates 5 times or so, pauses, quickly vibrates 5 times or so, pauses, and so on. It doesn't appear until about 50 mph, and I've not had the car much above 55. (No need to hurt a 50 year old legend is there?) I've had two brand new sets of tires AND wheels on the car in the last year. At present Coker radials are installed. Today I had the car aligned. I watched the job being done and even the technician said that it wasn't far off to begin with, and is darn near perfect now. In the short drive home (say 5 miles at 55) the shimmy is still there, but seems somewhat less in severity. The only other thing I can think of is to disconnect the propeller shaft and turn it through 180 degrees and refasten, thinking that its original balance indexing was mismatched during assembly. Anyone have any other ideas? I'm at a loss here.
 
I'm open to all ideas on the subject , and I will certainly check those out in the near future, and report back. Thanks! As an update, today I went back to where the alignment had been done to say that the repeating shimmy at about 55 mph was still there, not in the steering wheel, but could be felt in the accelerator pedal, the floor and the back of the seat. Up on the hoist we found all 8 rear spring u-bolt nuts loose. When tightened up, that in itself made a huge difference in the car's handling when you backed off the gas, the rearend no longer sidestepped. But ... the shimmy remains. I'll report back.
 
G_lower,
I checked and retightened the rear universal bolts, and checked the tranny mounting bolts. The shimmy remains. I'm at a loss. I think I'll try turning the prop shaft through 180 degrees and refastening, and if that doesn't do the trick, I'll change garages and have the entire driveline inspected and retightened front to back, and then redo the wheel alignment.
 

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