start with basic's, tires all good? (same pressure n treads). if so its in the front end somthins loose or busted, balls joints and tie-rod ends are very likely suspects, check them all. but beyond that more info is needed to get the right help..............lift? tires?
"Severe" Death Wobble is something I've had and dealt with. The usual trigger for DW is a front tire that has either become unbalanced from losing a balancing weight, or the shop never got it balanced well enough to begin with. A big Jeep tire that isn't spinning true easily imparts the energy to cause the front-end to shake so bad you will see your life passing before your eyes.
I'd #1 go have the tires PERFECTLY balanced. Tell the guy doing the balancing that is usual "good enough" job won't be good enough for your TJ. The type of front-end the TJ and a lot of newer trucks have is especially sensitive to imperfect tire balance.
Then #2 I'd do as advised and do a "dry steer test" to see if something is moving that shouldn't be. Basically, with the tires on the ground, have a helper repeatedly turn the steering wheel back & forth while you closely examine the front-end and steering system for something moving sideways that shouldn't be. Especially make sure the track bar isn't moving back & forth sideways indicating a bad bushing.
My last Jeep was a Rubicon Unlimited Sahara 2 door TJ It had a 2" lift and I ran 32's. It developed severe death wobble.
It turned out to be one of the tires had a tread irregularity. You could not see it until it was spinning on the balance machine, one section of tread was considerably higher than the rest of the tire. It would have been covered under the tire warranty but I did not save the paperwork.
So give your tires a close look when you get them balanced in addition to the advice above.
I've had the Death Wobble maybe 2 or 3 times over the last 17 years ... and each time, it was alignment issues. So in Jerry's item #1 ... that was what I ran into ... stuff like that pissed me off to no end.
I just had my first Death Wobble yesterday. I had my wife wiggle the steering wheel while I watched underneath. The bolt holding the track bar on the suspension end was slightly loose. I tightened it up and no more wobble. I'm going to check if the hole had been elongated ASAP.
"Dry steer test," is a terrible name for what it is, but it's unique enough to bring up some good stuff when you Ask Jeeves...
Making sure all your wheels are balanced is a pretty good start, but going off my personal experience from solid front axle trucks like the Wrangler (or my Bronco...do you need to buy a Bronco??), I suggest that before you go spend money on ANOTHER balance, that you pull the front wheels and clean anything off of the inboard diameter of them. Grease and road grime can make some serious imbalance issues and I'd hate to see someone spend money to balance dirt on the wheels!
When I was diagnosing a death wobble on my wife's new-to-me '06, I found a TON of garbage stuck on the inside of the wheels and pulling it off was enough to cause the wheels to vibrate because they had been balanced with all that crap on them.
After cleaning, that "Dry steer," thingy can help you diagnose loose components that may or may not have anything to do with your death wobble. If stuff is worn, it needs fixing, even if it's not causing an obvious problem. That track bar of yours is probably worn if it's over a few years old.
Any other suggestions on top of all of that is looking into some search engine magic...this isn't a new problem and very little of it is hard to fix, especially if you've caught your problem early.
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