Jungle Rot comes back to TN!

[glenn]

Caster will cause death wobble as will any worn or loose components. Check the kingpins for looseness. I'm wondering if having your ram hooked up might make the death wobble go away, kind of like a steering dampner.

[Stavesacre]

Ok so I went through and didn't several things to attempt to eliminate the death wobble I was experiencing at low speeds. I did all of them at one time and I didn't check the ride after each one, so I'm not exactly sure which one had the greatest impact, but the difference is night and day.

• I got my hydraulic ram in from West Texas Offroad and got it installed
• Rotated and inflated my tires as they were a little low
• I went through the whole front end and tightened every connection. I found one or two that they pretty tight, but probably not as tight as they should have been.
• I adjusted the tow to a little over 1/16" tow-in.
• I tightened the springless kingpin preload. The standard procedure for setting the pre-load seems a bit, well, open-to-interpretation. I found somewhere that as a general rule of thumb, the preload should be roughly around 15-30 ft-lbs on the set screw. Mine was much less than that. So I tightened it up.

So after doing these things here's what I noticed:
The whole front end feels more solid and stable.
The front tires don't seem to be wondering like they were before. Previously, it felt like I was giving the tires a general direction that I wanted the truck to go, but they had some free-will in how to get from A-B. I think I had my toe in set too much (or too little) which was causing the wondering feeling and the excessive tire wear (it was noticeable wear within ~100 miles )
I tried hitting bumps at various speeds and I never once got it to go into a death wobble. It still feels like there is much more side to side movement in the suspension than their should be. I suspect that the damper is preventing the death wobble from propagating, but the root cause may still be there.
I notice that if I push straight up and down on the leaf springs on the M715 they seem much stiffer than the springs on my Ram 1500. But if I push side to side on the M715, there seems to be much more movement than on my Ram. I'll do some closer inspection when I get a chance, but it appears that the bushing between the shackle and the springs is allowing a lot more movement than I would have expected.

[Stavesacre]

So after 3 months of everything working perfectly and the truck driving great, the low speed death wobble has come back all of a sudden. I've done lots of research and poking around and have some ideas of what MIGHT be going on. But I want to see what everyone else thinks!

It happens whenever I hit a bump with only one wheel below about 20 mph. Above 25 mph or so, you can hit anything you want with either wheel and it doesn't feel even remotely unstable. Also, for most other people, DW happens at higher speeds, but I've had it up to 75 mph (according to my phone) and it felt completely stable....just lots of wind noise. I went through all the heim joints and they all seem tight with no play. The steering box is new and there doesn't seem to be any play in the steering column. I'm also running a 6" x 1.5" hydro assist ram (which I think was just masking the real problem). And I'm running high steer with cross over steering with the drag link about as parallel to the tie rod as you could ask for.

I stuck a GoPro under the truck to see what was going on. I was a little shocked by what I saw. The whole axle is moving back and forth several inches. It appears that the shackles are allowing an excessive amount of play. My first thought was to start by replacing all the bushings, but after some research, I'm wondering if putting a panhard bar on would be a better solution. The problem is self propagating. As the axle moves to the right, the drag link pulls the wheels to the left which then starts the axle moving to the left and so on and so on.

Any thoughts or suggestions?

https://www.youtube.com/watch?v=7q1zHNsyAWg

[ray steadward]

Could be all of the spring/ shackle bushings. You could try swapping to poly bushings. My CJ does that when the rubber bushings are shot. I didn't see where the caster was set?

[Mikel]

Everything is going to flex when death wobble occurs, as the loads are immense. What is interesting is what happens before the death wobble.

I would check that caster is in the 5-9deg range. Then look for slop anywhere in the steering/axle.

If the axle (looks like a kingpin D60) is old, it may help to shim the kingpins or replace them, as well as the springs.

Good luck.

[Mikel]

I hope you don't mind that I took the liberty to post the video at POR. Hopefully you'll get some useful feedback.

http://www.pirate4x4.com/forum/gener...ble-video.html

[Subybaja]

Axle movement was going to be my guess. My truck is on an F350 chassis that came with a trackbar. The PO lifted it 4", and left off the bar. I had terrible DW, added a bar to the existing brackets, and it went away entirely.

Is 1/16 enough toe? I remember 1/8 being the standard recommendation, and with your big tires it wouldn't take much linkage flex to end up at zero or negative toe...

How do you like the OX? Next time I have $1100 laying around, I want one.

[Mikel]

If caster and toe are OK and there are no sloppy components in the steering, a steering damper would probably help. It won't stop death wobble when it is underway, but it will probably help prevent it. Your axle should already have the mounts for it. If the axle has a lot of miles, shimming or replacing the upper kingpins will help too.

I had some bad death wobble in my friend's M715 with a GM D60. We fixed every sloppy area and shimmed the kingpins. It went away.

[Stavesacre]

Thanks for all the replies everyone.
I'll check the caster angle when I get home and see if that might be a culprit.
1/16" toe in might not be enough. Initially I had it somewhere around 1/4" and it chewed my tires up like there was no tomorrow, so that's why I went with only 1/16". It might be worth increasing to 1/8" and just keep an eye on tire wear.
I agree that the bushings appeared to be shot. At the start of the video, you can see how much lateral movement there is when simply turning. Those long shackles and the SOA setup generates a lot of torque at the bushings.
The kingpins are suspect in my opinion. I have Artec high steer arms that use a springless design that rely on a set screw to set a preload. I'm very suspicious that after some driving time, the kingpin bushings settle and the set screw needs to be tightened. And the more you tighten it, the more load you put on the bushings and the quicker you wear them out. Kingpin rebuild kits are fairly cheap, so this might be worth my while.

Mikel, thanks for posting that to Pirate. For some reason I can't log in right now, I'll try again later today and post up on there too.

Subybaja, I haven't gotten to try out the OX yet cause I don't currently have a front drive shaft! It's next on my list after I get this DW sorted out. I did have some issues with getting the locker to engage and disengage with the manual cable, but I've read online that it requires a bit of fine tuning to get it dialed in, so hopefully that won't be an issue.

[Mikel]

I didn't notice the hydro steer. Never mind my comment for a damper.

Are your tires balanced? Sometimes weird things cause death wobble. I had a truck with warped front rotors that would start DW'ing when I stepped on the brakes at a certain speed...