Help with shimmy

[Medsker]

I have a shimmy. This is on my new Rubicon. It has under 5000 miles. This is the story. It started when I put on 33X10.50R15 BFG Mud Terrains. I believe these are balanced correctly as I worked at Sears Automotive for nine years and was present when they were done and the balancer was calibrated right before they were balanced and since the balance has been checked three times. The shimmy happens at 55 MPH. I have checked the alignment. Caster was at 6.5-7 degrees. I have installed adjustable LCA and adjusted them longer and shorter with no affect. This would have lowered my caster to about 5 and raised it to about 7.5. I have installed a rancho steering stabilizer which made the shimmy less but is still quite violent. I have checked all the torque on the bolts on the track bar, upper and lower control arms, ball joints and tie rod ends. I checked the track bar to make sure there wasn't any movement on it. I have replaced the long adjuster on the tie rods thinking it might be bent a little. I am at my wits end. It has a 2" puck lift on it with BPE on the stock shocks.

So any ideas?

Help?

Thanks Medsker

 

[Milner]

Have you checked the toe? These frt ends seem to be very critical when it comes to toe. The larger diameter of the new tires could have changed it just enough. My other suggestion would be to raise the trac bar higher on the axle. As the angle gets steeper the axle moves further side to side and things become exagerated. I know this helped a great deal on several XJ's that had shimmiy issues.

 

[Hickey]

Ditto on the toe. The 2" pucks would make you toe in a little.

 

[RockMonkey]

How much shimmy are we talking about? A little at a certain speed, or so much violent shaking that you have to nearly come to a near stop to get it to go away (death wobble)? If it's a shimmy, and not death wobble, I would try moving your front tires to the rear and the rear to the front, then drive it and see if there is any change. The wobble on my TJ was due to unbalanced front tires. Yours could be that, or a slighty bent wheel, or an out-of-round tire. I've seen brand new wheels wobble an incredible amount.

 

[Medsker]

It's definately not death wobble, its more of a shimmey like when your tires are way out of balance. It stops when you slow down or speed up 5-8 mph from where it is happening. I did try rotating the tires and it had no effect, I also tried rotating the spare to the front left and then to the front right with no effect. The alignment was just done twice. The first time is where I thought the tie rod adjusting sleeve might be bent (the one that goes all the way across) so I replaced it with a heavy duty one and re-aligned it. My left toe is sitting at .14 (spec is between .09 and .21 for both sides) and my right is at .13 with my total toe at .28 (spec .18 thru .42) I haven't tried raising the track bar. I have a complete 4" ultimate full traction lift that has a fairly heavy duty track bar on it but you have to lift the jeep 4" to use it. Since I'm only 2" right now it won't work. I really don't want to go 4" high since I believe in lower is better but that may be the next step is to put on the whole lift and see if it goes a way although I can't imagine it would since the only change to the front would be the track bar, springs and shocks since the UCA and LCA are already on it.

 

[RockMonkey]

Mine did that right around 45 MPH, and it went away totally when I got the tires balanced. You could try swapping on a completely different set of tires and wheels (of the same size) and see if it does the same thing, at the same speed. Then at least you would know if it's something about your tires/wheels, or if it's something about your steering or suspension that has been exacerbated by the larger tires.

 

[PierCed_3]

Mine did this for a while right after I bought brand new tires/rims. Come to find out that the tire had a "heavy spot" in it but it wasn't a factory defect so there was really nothing I could do with it. I also had a bad rim (it too had a heavy spot where the rim is welded together). When they were put together and the heavy spots were opposite of each other it helped significantly. IT is still cannot be on the front of the Jeep but it does what it is supposed to do so I don't care .

 

[Medsker]

Mine did that right around 45 MPH, and it went away totally when I got the tires balanced. You could try swapping on a completely different set of tires and wheels (of the same size) and see if it does the same thing, at the same speed. Then at least you would know if it's something about your tires/wheels, or if it's something about your steering or suspension that has been exacerbated by the larger tires.

This is a good idea to eliminate the possibility all together. Although unlikely all my tires have the same type vibration I've definately seen stranger things. My friend has a yj with 32" tires that I'll have to have come over and we can swap out and both go for a test drive and see what happens. Like you said it would either eliminate or get me a new set of tires, one or the other.

Medsker

 

[Milner]

What sort of air pressure are you running? try a little more or a little less and see what happens.
Also, in my experience .28" is a little too much too in on these setups. I know it is "within spec" but those specs are for a stock vehicle with stock tires....

 

[Medsker]

I'm running 30 psi on my air pressure. I'll try upping and lowering it. I'm up sledding at Bear Lake for the week but will have to play with the alignment spec a little more when I get back.

Medsker

 

[Badger]

another question is did they balance one side of the rim or both sides.if just the inside edge is balanced you are not truely balanced .

 

[Medsker]

They are dynamically balanced not statically.

Medsker