Hi-speed shimmy on a straight axle-39 Ford

[manyolcars]

I got my front wheels balanced but still have a shimmy that shows up about 55mph and I cant remember what causes it. Any suggestions? bad wheel bearing? toe-in? what else is there? Thanks guys

[C9]

Loose front end components and possibly not enough caster.
More than likely you've thought about that.

One trick the old timey alignment shops did with the Ford front axles was to run 3/32 - 1/8" toe-out.
Sounds strange I'll admit, but it was probably used when the front end was a touch worn.
I understand the car handles just fine and the shimmy does go away.

Keep in mind if you're doing the alignment bit at home, most garage floors are 1 degree + so as to drain water out.
If you're running say 4 degrees and adjust caster with the nose of the car to the inside of the garage you may have less than 3 degrees positive caster.
Positive being defined as kingpins tilted to the rear of the car.

Keep in mind the rubber rake as well.
A change in tires can make quite a change in caster.

[C9]

One other one I thought about, get the wheels off the ground, set up a pointer and spin the tire/wheel combo by hand.
You may have a seriously out of round tire.
Been there, done that and it drove me nuts for a while.

[deuce]

try switching the front tires side to side.

[manyolcars]

I should have said I've looked at all the tierod ends--all good. The kingpins are low mileage, The spring shackles are excellent, tires are low mileage with no wear showing,I've been driving this truck about 10 years and the caster has not changed. It has split radius rods, I checked those tierod ends, too. Its the left front wheel, I just had it balanced last week--I hope the guy looked to see if it was out of round--they usually will tell you they cant balance it. Its not the shock absorbers. It used to run straight with no hands at 70. Several years ago, a shop set the toe-in at 1/8th inch and it 'darted'. I increased toe in and it has been fine for years. Surely toe out would not be good, but I have wondered if I should increase toe in. Could the right wheel cause the left to shimmy? Its nagging at me that I am supposed to know what causes this --I cant remember. I wanna go to the Sherman Denison show this weekend but 500 miles of shimmy aint no fun.

[DrJ]

Check the alignment... again.
Did the guy put all the weight on the inside so the wheel would look clean?
That's ok on the rear but on the front it'll give you a lateral inside to outside imbalance, and make it shimmy.
I had some wheels that were computer balanced that would shake at 70 but be ok at 75..
The guy at the Firestone store told me I shouldn't drive so fast. I told him to preach to the wife about speeding and please put them back on the machine.
They both took an additional 1/4 oz weight in a totally different location fromthe other weights and that cured it!

On the toe out. when you have the typical Ford 6º caster the weight of the vehicle is pushing forward on the tires more than road drag is pushing them back so toe out keeps them pointing straight.
Yes it's backwards thinking to a car with 0º-1º caster. Road drag is making those cars want toe in.

[manyolcars]

1 oz outside, 1/2 inside I guess I will experiment with toe in tomorrow.

[manyolcars]

I spent a while yesterday expermenting with toe in and toe out. Any toe out causes the truck to 'dart'. More toe out causes 'darting' that will scare you bad! 1/8 toe in keeps the shimmy to an unaceptable minimum. I'm gonna drive it to Sherman/Denison anyway. Better give me a wide berth if you see me coming.http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[flt-blk]

Did you meet another cinder block on the highway like you
did in the 57??

I'll keep an eye out for you on the road.
TZ

[manyolcars]

I dont want to admit how much I tore up my 57. I turned off 360 onto the sidestreet that led to the swapmeet in Arlington Tx. I stayed in the turn lane, had no reason to go to the left lane. It was early in the morning, still dark. There were no signs, painted lines or anything to indicate my lane would end dead centered on the concrete curb. As soon as I saw it, I whipped to the left which was good. Instead of smashing my crankcase and ripping the transmission up thru the floor, I hit on the right front bumper, pushing it back into the fender, pushing it back into the door so it wouldnt open. Then the right front tire burst, the front rim bent waay too much to ever repair and the right rear tire burst and ruined that rim too. I put the spare on the front and drove 2 miles to the swapmeet on the rear flat. At the swap I bought another wheel then realized how bad the front end was bent. I bought an idler arm bracket and ran the toe in out to where it looked ok and drove 190 miles home at 60 mph. At home I found the lower A-arm badly bent and the 2 week old lower ball joint stud had stretched and bent. Some Hambers helped me fix my car in the parking lot and I sure appreciate them!

[Missing Link]

I am going to show my inexperience with suspension by axe-ing this question:
What is a good way to check the front suspension for worn parts? Tie rods, etc. I have a similiar straight axle setup and seem to have the same issues. Although I do believe that the roads in my area have something to do with it, I would like to know what the best way is to check the front suspension components correctly.

[safariknut]

You didn't say when you first began to experience the shimmy or why the need to re-balance the tires.What type of tires are on the car now?Has the car been sitting for a period of time?Have you had to make any panic stops lately?Hit any potholes or curbs?
It really doesn't take much of an impact to damage a tire.I can recall my cousin having some low speed shimmy problems on his 32 roadster but that was caused by the tierod flexing when going over a bump(such as railroad tracks)about 15 mph and setting up an oscillation in the front wheels that could only be stopped by coming to a complete halt.A steering shock from a Jeep on the tie rod solved the problem.
As far as darting goes,you didn't say how much you weighed but I recall when I worked at the dealership we had a car that we aligned the front end,tech took it for a test ride and was fine(he weighed about 140).The owner picked it up,drove out the door and drove right back in complaining it pulled violently to one side(he weighed 300+).We finally wound up aligning the front end with him sitting in the car!Worked great!
Just some thoughts.

[deuce]

i once had some really crappy www radials on the front of my coupe that would start that oscillation problem after going over a small bump in the road, and would only stop when the car was stopped. i checked the tech section on fordbarn.com and found the answer- rotate the tires. since i have big and littles, i just swapped the fronts side for side. problem solved. i then got rid of the crappy tires and replaced them with bfg silver town radials, and haven't had a bit of problem since.

[Flat Ernie]

Don't know what's causing it - sounds like you've checked all the right things and gotten good advice here. Probably tires, but steering damper should do the trick...

http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

[Nads]

DrJ, I hear you about balancing with weights on the inside only. I did that the first time around for cosmetic reasons. I had a vibration at 65. This time around when I put on the new wheels I had them properly balanced. The vibration's gone. It's just not worth it to take risks over cosmetics.
Have you considered a Panhard bar?