Death wobble

The JEEP is beating me.

I've got new main eye and shackle hanger brackets mounted. I was very careful to take several frame measurements, and the JEEP sits nice and level now. Unfortunately, it doesn't drive that way.

I've got this incredible bumpsteer at 30mph. The whole front end shakes violently and the steering wheel moves side to side rapidly. I've pulled it back in the garage several times, tried toe-in, neutral, and toe-out adjustments. Does the exact same thing in all three alignments. 25mph I can drive all day. 30mph it starts shaking. Once it starts, I have to slam on the brakes to get it to stop, then I can drive 25mph again. I've lifted the front end and checked for run-out, loose caliper bracket/hub, loose tie rods, loose spring hardware. Everything seems tight. I'm almost at the point of paying someone else to fix my JEEP. Any suggestions?

The really frustrating thing is, the JEEP drove and towed straight when it was leaning.
http://www.earlycj5.com/gallery2/v/trail/Randolph/LaborDay06/PICT0073.jpg.html

 

Probably an omen... I was your 666th post on a thread titled "Death wobble". I think I'll go buy more life insurance tomorrow.

No frame cracks that I can see (although there will be if the shaking continues).

Steering box is really good for a stock Ross setup.

Wheel bearings are relatively new and visually I see no obvious run-out. I slowly rotated the front tires and tried to shake to see if there is any play, but nada, nothing, zip, zero. The front end seems really tight.

I'm thinking about two different things at this point:

1) I've got a little gap between the bracket and the shackle. I used thick washers as a spacer before, and tightened the bolt down really gud. This time around, though, I used these fancy rubber bushings from Krage's. They've got a lip on them that fills the gap, so no washers. I'm wondering if this rubber might be too soft and is allowing lateral movement.

2) This is a reverse shackle setup, and I've got the shackles vertical now, or very close to it. I'm wondering if this is allowing my relatively soft springs too much front to rear movement (relatively small bumps allow the spring to compress and move further to the rear than before).

Neither one of these hypotheses account for this only occurring at 30mph.

 

Well, I didn't necessarily change the shims or anything, but now that I think about it, moving the hangers to their correct location did increase the distance between the frame and the rear of the leaf, which would have brought the knuckles closer to parralel with the ground. (can't remember if that is positive or neg direction)

King pins, drag link, TREs all seem good.

I used the same alignment procedure as before I went to Tuttle, but maybe I'll throw it on someone's rack tomorrow and see what it reads.

 

"Looking out the window at the frontend reveals the tires dancing back and forth like a couple of cancan girls."

That's me! Thanks for the link. I'll check it out.

 

I was driving home on the interstate a couple nights ago, and came up on a girl in a late-model Jeep. Her front wheels were thrashing so violently it scared the hell out of me, and I moved over two lanes because I was sure parts were about to start flying. I've never seen anything like it! I don't know late-model Jeeps, but it had rectangular headlights.

 

Ditto on the alignment. Fixed it for me in my XJ. First time it happened, scared me to death. I had just put on the new lift and was driving it home down the interstate. Once I got to about 60, hitting a bump just right would set it off and I'd have to come to a complete stop and start back again.

 

anything like this?

http://www.emotoman.com/videos/dw.mpg

 

I'd still start with the kingpin bearings and races... You've described speedy to the letter. Kingpin bearings fixed him right up

 

Correct, but all it took for my Kingpin bearings to show the death wobble was a new set of tires... It's an easy swap and it can be done in an afternoon. Peace of mind...

 

That is exactly what my JEEP is doing.

I am positive the kingpins are fine. With the front end on a jack, I have zero slop while grabbing the tires at 12 and 6 on both sides. I also have no slop when grabbing the tires at 9 and 3; as soon as I move one, the other moves. When I spin the tires, I get no grinding or visible wobbling.

This is something that literally happened overnight. Drove fine with the "jeep lean", death wobble with the new shackle position.

I am asking myself, what has changed?
1) The position of the shackle hangers has changed, but I am confident they are where they need to be now.
2) The toe-in has changed, but I have tried various different toe-in positions and get the same results.
3) The shackle bushings have changed; they are now a very soft rubber (I am going to try to swap these out for my washer arrangement just to reduce variables).
4) My castor has changed; I've got around a 6deg shim installed, but moving the shackles reduced my castor by a degree or two.
5) To my knowledge, the balance on my tires have not changed, unless I accidentally knocked a weight off without noticing. I am going to swap the rears to the front and see what happens.

 

In terms of stock suspension, every old jeep I ever drove would do this, and in every case it was kingpin bearings that finally really fixed it.

I realize you may have altered the alignment also, but new well adjusted king pins bearings can't hurt. IMHO.

Pete

 

One thing that has changed that I didn't previously consider is the crazy angle added to my tie rods:

I put on a massive toe-out and it was driveable. I thought that was an indication that perhaps my home-brew alignment skills were not entirely accurate, so I took it to a shop. The tech took one look at it and said "You will never cure bump steer until you fix these angles."

While I was there, the guy shook the front end, turned the wheels, etc. and confirmed to me that bearings/TREs/steering box/bell crank/hubs all seem good and tight.

I've got an extra set of knuckles I purchased from $sink sitting at the machine shop getting reamed out for a tie rod flip. I need to light a fire under his butt. I've got an AA knuckle-to-knuckle rod in the garage, and known good TREs. I think I am going to install the new parts, set the alignment, and see what happens. Looks like I won't be going to the trails this weekend, though.

 

My rig is also a 70 & I've gone through a few trials with dw.

Last year it turned out to be a worn out drag link. TRE's would be just as bad. Anything that will allow slop or play side to side can set it off.

In your case I think the bad angles made the effect much worse than normal but I don't understand how just a bad steering link angle can cause it. From my research death wobble is the newton thing with an action (force) getting an equal and opposite action. One tire pushes towards the other and the second tire pushes (bounces) back. Yes, it can be brought on by angles (toe, caster, etc.) but the bad angle is just what sets up the shaking. The actual death wobble needs some slack or slop to keep going. I think it could be a very small amount of slack that's hard to feel by jacking up the front end and grabbing the tire and pushing back and forth - it could be less slop than you can detect doing this.

I think you mentioned longer shackles? or that yours were straight up and down. It's possible that you're getting enough play in the shackles to get the shaking. Do your shackles have a cross bar? Don't know if that would help but it might. I think it's hard to detect slop in the shackles by jacking up the tires and turning by hand.

Keep us updated & good luck.

 

Forgot to post earlier that I've ruled out tire balance as well.

Been playing with it some more (way too much today considering I've got a big Physics test in a few hours). I think it's a combination of things, but AKCJ might be right about the shackles. I had a buddy shake the frame while I sat in front looking directly at both shackles. Know what I found? Those bushings that I let Krage's talk me into are so soft they're allowing the shackle bolts to move up and down within the hanger, which is translating into a lot of lateral movement. I am going to pull those out and stick in the piece of tubing with harder rubber, then put washers in the gap between the shackle and hanger like I originally had. Won't be able to do it today, but will post results when I get them.

With the massive toe-out I've got on there now (almost 3/8" or so), I think I can drive it on the trails. If I get a trailer, I might make it down to Kansas Rocks this Saturday.

 

Sonds very simple but it worked on my jeep - Toe out = front end alignment. In addition I installed a steering stabilizer which reduces road feedback and is nice off road dampening feedback in the steering wheel. My jeep had a bad wobble before the alignment.