Below is a modification of what I posted here:
http://www.ford-trucks.com/forums/12836 ... 40mph.html
The best thing about that post, was that one of the persons whom I most respect at FTE, Cleatus12r, agreed with me. He also made a comment about ladder bars, which may pertain to you.
OK, I will get flamed for what I am writing below. It is considered heresy, but it is based on my extensive personal experience with DW and how I eventually cured it.
First, don't focus on what "initiates" the DW. You can and should fix that (i.e., by replacing a warped rotor, replacing a warn bushing or ball joint, etc.). But if your set up has the propensity to "propagate" DW then something else will initiate it, and you will be chasing down that initiating event, rather than curing the DW from propogating. (I mean it is not a single isolated bump steer that scares you correct? It is the resulting "wobble" back and forth that can kill you going downhill into a turn on an icy road with a big rig coming towards you uphill or when you are going downhill pulling a tandem one yard concrete mixer. Both of which I have experienced with DW.)
Adding the Energy Suspension track bar bushing and tightening up the steering box (both of which I did) just makes the propagation more efficient and more likely
to oscillate more violently.
So here goes, IMO, "Death Wobble" is caused by one tire (e.g., the left) hitting a bump and pushing through the tie rod up against the rubber sidewall (which is, effectively, an undampened spring - it is rubber filled with air after all -- you know how a rubber basketball filled with air bounces?) of the right tire causing a "bump steer" to the right resulting in a reaction of the right sidewall springing/pushing back through the tie rod to the rubber sidewall of the left tire which repeats with increased violence until the vehicle stops or nearly stops rolling. This is best seen in your third video - Ultra Low Speed - where you can see that the tie rod is moving left and right while, as a reference, the differential immediately behind it is relatively stationary:
That is the oscillation commonly called DW. The steering wheel vibrates violently back and forth as the tires violently wobble side to side, one tire punching the sidewall of the other tire and that tire punching back through the ineffectively dampened tie rod.
The reason that tightening up my steering box or replacing the track bar bushing caused my DW to actually get worse is because those things actually increase the effectiveness of the bump steer by tightening up the suspension!
In my experience of chasing down Death Wobble, it has nothing to do with the track bar, ball joints, or caster. It is merely an undampened spring (with the air-filled rubber sidewalls of the two front tires being the springs). Yes, find and replace worn components, I am only saying some brand new
Fords and Dodges with coil springs and solid axles have DW right from the factory - brand new!
So, after avoiding DW for only one year after $3,000 of front end work and a set of brand new tires (Toyo Open Country AT's), at TurboStew's suggestion (see link to his post below), I installed dual opposing Bilstein gas PRESSURIZED SHOCKS (not stabilizers) using a Rough Country dual stabilizer bracket which I cut up and re-welded for a custom fit. And in thousands of miles all over the Western US and Southern B.C., I didn't have a DW since.
http://www.sportsmobileforum.com/viewto ... 9&start=15
BTW, the opposing gas pressurized shocks push against each other thereby cancelling each other out and, thus, do not put any pressure on the steering box while an opposing dual stabilizer set up (a stabilizer has resistence both pushing in and pullling out) would create tremendous resistence on the steering box (possibly causing premature wear and looseness).
In summary, for those of you who have had DW, you wouldn't drive your truck without vertical shocks at each wheel to dampen the sprung mass of the body, would you?
So why would you drive your truck without horizontal shocks connecting the tie rod to the differential to dampen the horizontal spring effect of the rubber on those big sidewalled tires you are putting on the front of your truck?
Finally, anyone who says that dual opposing gas pressurized shocks used as a steering stabilizer are just "masking" the underlying problem is . . . in polite words: "mistaken."
For those of you who believe that . . . , please take off the vertical shocks at each of the four wheels on your truck and see if you like driving it while it bounces uncontrolably up and down without the benefit of "masking" which the vertical shocks provide by dampening the vertically sprung mass of your truck's body.
On a stock van, the hydraulic steering box is the only tie rod dampener. It is marginal at best and cannot provide sufficient dampening with a larger than stock tires or with 4x4 hubs or larger brake rotors added to the wheels. Both larger tires and 4x4 lockout hubs and larger brake rotors add mass at the end of the tie rod which the stock steering box cannot dampen effectively.
You added hydro steering. I thought of that too. Because hydraulic steering is hydraulic it inherently provides extra tie rod dampening to that provided by the hydraulic steering box. (But hydro is from what I read great for slow speed rock crawling but can cause unpredictable immediate lane changes at highway speeds, so I passed.) I provided the required additional tie rod dampening as described in the sportsmobileforum.com thread above. Your set up is extreme and in my limited experience needs extreme tie rod dampening. So, you may want to add what Turbostew and I did to your set up as well.
As far as whether or not increasing the sidewall height of the front tires by going to a bigger tire would increase the likelihood of DW or not, I prefer not to speculate. The internet is an echo chamber of misinformation. I have read lengthy posts by people who have never had Death Wobble telling other people who have it that it is their track bar or their ball joints or their caster -- even on brand new F350's!
I already mentioned spending $3,000 with the 4x4 converter only to have the DW return in 2 years. The only thing that made it go away for a while was replacing the front tires (with half the tread left!) with new ones (Toyo AT's). I then bought a used 600lb. Snap-on torque wrench and checked my track bar bushings myself. They were fine (they were only 2 years old after all).
Then I found TurboStew's post on the opposing dual gas pressurized Bilstein shock absorber steering dampener set up and in the years since installing it, I have not had DW once.
How much you want to bet that if I drove my van without the opposing dual gas pressurized Bilstein shock absorber steering dampener that I would have DW immediately again?
Finally, IMHO, there should be a moratorium on people who have never had DW from suggesting to others how to fix it.
[Flame suit on, visor down...]