Front end shimmyi

Chris H

Chris H

Senior Member
Hello, all. It has been a while since I posted anything here. I am having an issue that has me puzzled. When driving my '30 Tudor, every now and again I get a little shimmy in the front end at low speed. I can usually stop it with a quick turn of the steering wheel, back and forth. When I carry passengers though it is much more pronounced, especially with someone in the back seat. The shimmy occurs at speeds of about 5 to 15 MPH. It is also much more difficult to stop. It also happens when breaking when I get near these speeds.

I have checked the king pins, front wheel bearings, replaced the tie rod end and pitman arm springs and cups, and removed the wishbone rubber ball and went back to the original configuration. All of this seamed to help, including rebuilding the 2 tooth steering box. The shimmy was reduced with just me in the car, but alas, it has never been eliminated, and has always remained with passengers in the car.

I have gone back and done searches thru this site looking for similar issues, but have not found a solution, yet. I am at my wits end on this. Any thoughts or suggestions? Thanks for looking.

Chris
 
Everything needs to be tight, all of the springs compressed at least 25% on the tie rod and drag link. The other cause is the steering box being loose on the frame. Check the two bolts that attach it to the frame, if not tight it will cause that exact problem.
 
Excuse me as I am probably stating the obvious...With passengers you are changing the caster angle and that is making your steering problem surface. Cause though, I am not sure. A couple things you could check yet would be toe-in and caster angle. I know if I have almost no toe-in on my Phaeton, it will get "squirrely" if I have passengers in the rear. A weak rear spring could be causing the problem with the caster angle...if the car is already riding a bit low, adding the weight of the passengers will change the caster angle to positive from its ideal or maybe already marginal setting and that will likely cause a shimmy.

I know you stated "low speed" and the info below refers to high speed...so I don't know.

Another check: If you can, lift the front and place two stout jack stands under it well spread so the front tires are off the ground 2 inches. Now grab each wheel and try to rock/twist the wheel hard...sideways...and look for areas of movement in the links, arms and steering gear. I think you may find your problem.

I found this online...ignore most of the info but look for the info on excessive positive caster angle.

Good Day!

Wheel Alignment: Caster Angle

caster-chart.webp

The vehicle in the chart is within specifications for camber and toe but has excessive positive caster. This excessive positive caster will cause a shimmy at higher speeds and excessive steering wheel snapback. This is why vehicles that specify high positive caster usually have a steering dampener attached to reduce any adverse effects.
Caster is read in degrees. It is the forward or backward tilt of the steering axis viewed from the side of the vehicle. Vehicles with SLA suspensions use the upper and lower ball joints to create the angle and vehicles with struts use the center of the upper strut mount and the lower ball joint as the angle. It is compared to an imaginary line down the center of the tire or zero caster.
Zero caster is when the tire is true vertical. Negative caster is when the lower pivot point (ball joint) is toward the back of the vehicle compared to the upper pivot. Positive caster is when the lower pivot is toward the front of the vehicle and upper pivot leaning away from the front toward the rear. Most vehicles have positive caster because it provides greater feel and stability, helps the wheels track straight and provides steering wheel return after taking sharp turns.
 
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Have you checked for out of round wheels. I do this by jacking the wheel up just enough so it is off the floor just so that it will clear the floor. Then turn the wheel and see if it stays off the floor the same all the way around. If not, you may have an out of round wheel which will have you floating up and down at slow speeds down the road.
 
Chris my car did the exact same thing. I rebuilt the front end but finally got around to replacing the steering knuckles. I could not tell if you did that or not. Now my car does not do it any more.

Mike
 
Have someone sit in the car and rock the steering wheel back and forth. While they are rocking the steering wheel start at the steering box and work your way through EVERYTHING checking for slop. It doesn't take alot of movement to set up a shimmy.
 
Make sure that wish bone ball is still round and it fits tight in the caps. Any little slop in it will cause a huge problem. Same for all of the steering and front end pivot points there needs to be no slop that you can feel by pulling, pushing......
 
Please check the SPRING PERCH TAPERED NUTS !! Many cars come into my shop and the 2 nuts are loose, also check spring shackles, wheel bearings, spindle arms, steering box loose etc. All of these items need to be checked

Mike
 
You could try (if you haven't already) switching wheels front to back. This might at least help you determine if a rim or tire is at fault.
 
Thanks a lot, guys. It gives me plenty to think about and check. I am making a list, as I am getting ready to put away for the winter. Yes, I did replace the worm & sector. (The original had been brazed & machined). As usual, this is the best resource for information. You guys & gals are fantastic and I appreciate all the replies. Thanks again!

Chris
 
1crosscut said:
Have someone sit in the car and rock the steering wheel back and forth. While they are rocking the steering wheel start at the steering box and work your way through EVERYTHING checking for slop. It doesn't take alot of movement to set up a shimmy.
Click to expand...
Right on, Crosscut!
It's usually caused by SLACK in the steering system. Have weight on the wheels when doing the above test. Turn it firmly to "lock" & back off a little & do it again, while you observe & FEEL each connection! Pay attention to the nuts that hold the steering arms to the spindles, a SLIGHT amount there can cause it! Vermin shimmied, with ALL new parts, one of the repro springs in a tie rod end was TOO SHORT! Make sure the pitman arm clinch bolt is TIGHT, TIGHT! TOO much SLACK in the steering box is also a common culprit, also! I've corrected MANY old Datsun & Toyota truck shimmys, with a simple sector shaft adjustment!
Bill W.
 
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