Terrible Frontend Shimmy

S

some mech 3

Member
My '31 coupe has a very bad shimmy. It occurs when I drive on secondary roads only. It never occurs on smooth pavement. The shightest bump the driver's side front wheel goes over produces the shimmy. The shimmy only stops when I apply the breaks. Some facts about the frontend: the tires are brand new; I installed a new front spindle bolt set for both wheels; the spindles have been reamed; the driver's side wheel has a new outer bearing with a new race; the passenger side wheel has only the new bearing; the radius rod bolt set has new bolts, springs, etc.; the balls on the spindles are not worn; there is no sloppy play in the tierod ends or in the draglink; the toe-in differs only by 1/32 inch from front to back. When I test the wheels for bearing ware after I snug up the wheel hex nut there is no play. I am at my wits end. Thank you in advance for your suggestions.
Sam
 
If you have jacked up the front end, placed same on jack stands, had a helper turn your steering wheel while you try to shake & test everything for looseness, & found everything to be OK & tight, then found camber & caster to be right on, sounds like it possibly may be a good idea to find:

1. A local Model A Club to ask for their trusted Front End person to visit you so he can "SEE" what you have; or,

2. Go to a front end alignment shop that has a gray haired old man or no hair old man to see if he can find anything.

3. Other than that, remove front axle & have it tested to meet Ford's original specs & have it corrected if need be.
 
1. toe in should be 1/8. 1/32 isn't much of anything
2. almost sounds like wheel bearings are too tight, but that wouldn't cause your problem. Adjust this way: with wheel spinning, torque hex nut to 15 #, then back off one full castellation and install cotter
3. be sure the pitman arm is very very tight to the sector shaft. Have someone gently turn the steering wheel back and forth a bit while you study the pitman arm attachment for lost motion...
4. how much play is in the steering wheel ? should be 2" or less at the OD. If more, do more gentle back and forth of the wheel while you check all steering attachment points for lost motion.

do these things and report back

5. Addendum. Are the lock pins for the spindle bolts really really tight? You do NOT want the spindle bolts shifting around in the axle at all.
 
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It might be your wishbone ball, or how tight you're "snugging" up your bearings, or your spring perches, or your front spring, or a bent axle or wheel, or out of balance wheels, or floatamotor mounts, or...? The geometry of the front end is a complicated thing. I fought this for years on my tudor, going through everything you've described and more, except the wishbone ball. I finally said t'hell with it and installed a front stabilizer bar. That ended the problem. I found a good wishbone and will install that this winter and try it without the stabilizer, but for now the shimmy is gone.

I set toe-in at 1/16" on all my cars, but there are many variables that can affect the accuracy of that. But my tires don't wear out prematurely, so I figure I'm pretty close.

Good suggestion from tbird about play in the steering box.
 
Check out the camber of your driver side wheel; axel may have slight bend up which would reduce camber.

On a good flat surface, lay a large metal carpenter square on the flat surface and move it up against the backing plate; it should touch the bottom of the backing plate and be about 7 degrees away from the top of the backing plate.

Ron
 
Checking everything twice does not cause problems.

However, no matter what is causing your shimmy, after checking 1,000 things, the remedy will always be found in the very "last" thing you checked.

WHY?

Because after finding the remedy, you quit checking!
 
have you had your front tires balanced? you need an old time shop that has the motor that spins the wheel on the car with the strope light attachment that goes under the axle, when the tire is spun if its out of balance the strope light will blink and show the heavy spot on tire, those old balancers are hard to find but are excellent for the model a tires
 
How tired is the spring and any wear in the shackles? If spring eyes are close to riding on the axle, things are worn. Snyder's sell a good replacement spring but I'm not sure on quality of shackles.
 
From your post, there is something still loose. And, it can be anything from the wheel bearings to the steering box and anything in between. How are the tie-rod/drag link springs and how tight are they ? The pitman arm has been mentioned, how tight is the box to frame ? How much steering wheel free-play ? Just too many things to mention and it doesn't take too much to cause it.
 
Are the nuts that hold the steering arms to the spindle REAL TITE??? A tiny bit of looseness can set up weird shaking. Bill W.
 
I don't think anyone asked you about the bolts holding the backing plates to the spindles, those should be tight as well.
 
As 700rpm said check your wishbone ball. You may need to put a concave washer to take up some slop.
 
Bill W you are so right. I constantly preach about the steering arms being tightened to the spindles. One reason I do this is because guys have a tendency to look at them and think, hmmm, those look like they couldn't possibly come loose. I chased a shimmy for a long time before I discovered they were loose on my car-and I had installed them AND tightened them using a long cheater. They were definitely tight when I assembled the front end, but driving a while loosened them up just enough to cause a slight and maddening shimmy. I must have had paint or something on them or the spindles when I installed them.
 
Greg Jones said:
Bill W you are so right. I constantly preach about the steering arms being tightened to the spindles. One reason I do this is because guys have a tendency to look at them and think, hmmm, those look like they couldn't possibly come loose. I chased a shimmy for a long time before I discovered they were loose on my car-and I had installed them AND tightened them using a long cheater. They were definitely tight when I assembled the front end, but driving a while loosened them up just enough to cause a slight and maddening shimmy. I must have had paint or something on them or the spindles when I installed them.
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Yep, Greg, they're easily overlooked, I never thought about them until Claude, our REAL GURU, told me about them. Vermin's nuts looked tight, but they tightened up by 2 nut slots.
Over the years, I've found that the REAL regular old shimmy is ALWAYS caused by SLACK somewhere in the steering & front end system. Many times it is caused by slack INSIDE the steering gearbox, either from wear, or from needed adjustment.
Vermin had all new tie rod ends, etc, but shimmied. The spring in the rear drag link looked NEW, but was about 5/16" TOO SHORT!! It looked SO loose that the ball might have even popped out!! (WHOA!!) Bill W.
(My smart a**ed Son asked me if I checked the Ackerman Angle?? He was surprised that I knew what the term meant, "And it's NOT adjustable, DUMB A**")
 
Is everything (springs and cups) in correct order inside the tie rod and drag link ends? And tight enough but not too tight?
 
I had that. The car was undriveable. It turned out to be everything!

I rebuilt the front end, new pittman arm, drag link, tie rods, steering arms, king pins, wheel bearings, brake drums, and tires.

Little by little it went away.
 
Someone once posted a pic about 1 drag link end that has it's parts loaded different than the others. Can you post that pic again, THANKS. Bill W.
 
I would look at front cross member where spring shackle is attached
to see if it is cracked in that area. I had that problem now resolved
by welding.

fredski
 
I had the same problem and it was the spring perch nuts. They have to be very tight.

Mike
 
H.L. Chauvin, tbirdtbird, 700RPM, Ron in Quincy, ford 3, gweilbaker, Patrick L., Bill Williamson, John LaVoy, Phil, Greg Jones, J Bill, fredski, and Mike: a huge thanks to all of you for your suggestions to cure the shimmy. I spent the last day and a half tightening the tie-rod and draglink endcaps, torquing the axle nuts to 15#, and checking looseness. I then drove the coupe over the bumpiest road in town and other secondary roads and did not get the slightest bit of shimmy. From reading all you posts the main thing that was mentioned was the importance of tightening everything that needed to be tight. You all are a Godsend. Thanks again.
Sam (some mech 3)
 
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