Death Shimmy

[dbdave26]

My car is a 1931 Model 866s sport coupe. I restored it about six years ago. It is a great car to drive and tour with. Late last fall while taking the boss for breakfast, we hit  a rough patch in the road. The steering wheel began to shake violently. Only way to stop the shaking was to stomp on the brakes real hard.  We went a little further down the road and it happened again.  We went home and put the car up for winter. this winter I jacked her up and checked tie rod ends , kingpins, draglink ends, and all parts related to the front end. I tightened the draglink ends as the manual talks about. I was able to tighten up the steering box. I also removed the front wheels and drums to check wheel bearings. I replaced the front brake shoes.( was planning to do that anyway to improve braking). First outing yesterday, brakes much improved, steering play much better, but had the shimmy show up on any rough patches in the road at about 30 mph. Any ideas of what I may have missed? 

Thanks Dave

[Guest]

Caster, Camber and toe in.  Spring shackles (all of them both front and rear).  Is your back axle square in the frame (wheelbase the same on both sides).  Are your wheel bearings adjusted properly, have your wheels been  balanced recently (they do go out of balance with use).

Death Shimmy is caused by something loose AND something out of adjustment or vice versa.

Edited May 5, 2020 by Guest (see edit history)

[21raceabout]

Last year had front end shimmy problem at a discrete speed in one of our antiques (not Buick).  In our case it turned out to be non-OEM sized wheel bearing on front passenger side was loosening up (slightly).  Unfortunately OEM size bearings are no longer available so stuck with the cobbled solution; just need to keep an eye on them now that they stay "tight".   Agree with comment above that could be any number of things are slightly loose and/or out of alignment.

[edinmass]

Set the castor to 1/2 degree positive, 1/8 inch toe in, and run 40 pounds of air pressure. If the front end is tight, the 1/2 degree positive will stop the shimmy EVERY time.

[Marty Roth]

18 hours ago, Tinindian said:

Caster, Camber and toe in.  Spring shackles (all of them both front and rear).  Is your back axle square in the frame (wheelbase the same on both sides).  Are your wheel bearings adjusted properly, have your wheels been  balanced recently (they do go out of balance with use).

Death Shimmy is caused by something loose AND something out of adjustment or vice versa.

 

Death Shimmy/Death Wobble is caused either by something loose OR something out of adjustment,

Or Both,

at least in my experience - it could be one or the other, or both,

Wheel balance and tire pressure surely can be contributing factors, but the above are more likely

[edinmass]

Placing the Castor to 1/2 degree positive stops the oscillation and has little effect on the steering. Most cars call for 2-3 degrees. If you read factory service bulletins from the 30's you will se the solution to the death wobble is tight steering components, 1/2 degree positive castor, and high air pressure. Fixes a car every time. We had a very low milage Model J that had a steering damper on it for over 50 years. Remove the damper and it shook like hell. Did the alignment the way I posted, and it was smooth as glass to 90 mph. I didn't touch the from end, as it was tight. 

[Brian_Heil]

Check your tire pressures too. 
 

I only get it when the tires are low. 

[edinmass]

50 minutes ago, Brian_Heil said:

Check your tire pressures too. 
 

I only get it when the tires are low. 

 

Not accurate..........you can get it under many different circumstances, read my post, I said to run 40 pounds in the tires.

[dbdave26]

Thanks guys.  I'll try to get my local tire guys to get it up on the lift to check further. I have asked about wheel balancing,and they tell me there is no way for them to do it. I know about the wheel studs for that purpose, maybe I can get them to spin balance on the car. I assume that is still possible.I'll keep working on it.

Dave

[Brian_Heil]

1 hour ago, edinmass said:

 

Not accurate..........you can get it under many different circumstances, read my post, I said to run 40 pounds in the tires.

Thank you, but please re-read my post.  
 

I said I only get it when my tire pressure is low. 

[Brian_Heil]

Lots of people read this Forum.  Trying to help others. 
 

A first check for solving death wobble is to check tire pressure.  Cheap and easy.  

[edinmass]

7 minutes ago, Brian_Heil said:

Thank you, but please re-read my post.  
 

I said I only get it when my tire pressure is low. 

Agreed...........my fault. I was distracted while reading and typing.