Death Wobble - Possible Resolution

[BajaSportsmobile]

Originally Posted by UJOINT

I would recommend more castor, +5-6 degrees is ideal.

I would agree with this.

More caster will cause your steering to want return to center - DW's are the steering turning away from center, so it makes sense that more caster will help.

[REF]

[emoji106], my rig will be there week after next. I'll post up the results with pics, looking forward to having things reworked on the front end for proper clearance and sway control, I hope I'm not opening up a can of worms with this one, haven't had the notorious DW, and don't want to start now! See you around....

[sidetrak06]

Originally Posted by REF

[emoji106], my rig will be there week after next. I'll post up the results with pics, looking forward to having things reworked on the front end for proper clearance and sway control, I hope I'm not opening up a can of worms with this one, haven't had the notorious DW, and don't want to start now! See you around....

Whether you know it or not...you opened the can of worms a long time ago. You just don't know how bit that can is yet...

[E350]

BajaSportmobile and Ujoint: You two are the people whom I wanted to draw out to critique my analysis of my cure for my DW. I write long posts so that I can put out my understanding for criticism so that I can learn from you guys. This is a subject matter that I have personal experience with and which I personally cured after the 4x4 converter failed to cure it despite work under warranty, $3,000 in extra work, and new tires all around (merely a temporary fix). See my responses in blue, below.

Originally Posted by BajaSportsmobile

You are suggesting that the "horizontal shocks connecting the tie rod to the differential [s:1u8wx8cu]to[/s:1u8wx8cu] dampen the horizontal spring effect of the rubber on those big sidewalled tires" - again, nothing dampens that except the tire itself. As can be shown on the last two pages of "Quadvan Death Wobble" which I linked in my post above, the dual opposing gas pressurized Bilstein shocks connect to the differential then eachconnect to the tie rod. I installed them and I assure you that they provide resistance to quick movement of the tie rod from side to side.

What the "horizontal shocks" dampen is the rotation of the steering knuckles on the ball joints steering axis - and the transfer of that rotation to the other steering components. At first I had trouble visualizing how the steering knuckles rotate on the ball joints, but I get it now. In fact, Turbostew said the same thing with respect to king pin axles below. But since the steering knuckles are attached to the tie rod and with the dual opposing shock set up the tie rod is attached to the differential aren't we saying the same thing? I.e., that the shocks are dampening the tie rod movement laterally?

Death Wobbles are the uncontrolled rapid rotations of the steering knuckles on the ball joints steering axis - for whatever reason. Whether that rotation is caused by design constraints, worn components, alignment issues or "tire spring" the steering damper are just "masking" the "problem". Again, since this phenomenon also occurs on some brand new unmodified Ford and Dodge trucks with stock tires, can't we say that steering geometry can sometimes not be part of the problem and in those (albiet relatively rare) situations, dual opposing shocks used as a steering dampener are not "masking" a steering geometry problem but are merely providing the necessary lateral dampening as I described?

Look to gyroscopic inertia around an ever changing spin axis for an understanding of DW's - that is why DW's are rotational speed sensitive (speeding up or slowing down the vehicle will stop DW's) and steering angle sensitive (turning will stop DW's). I have never had this thought before and I get it.

Bigger tires have greater gyroscopic inertia, worn components, a different scrub radius due to wheel offset, and other designed in factors create an ever changing spin axis all contribute to Death Wobbles. Yes, I am aware that my wheels have a larger wheel offset and that can contribute to DW as well. But again this is cured by dual opposing shocks used as a steering dampener while I bet dollars to donuts that paying for regular offest wheels would not cure it.

I like the term "dampening" better than the term "masking." For the simple reason that it actually describes (obviously we disagree) physically what the dual opposing gas pressurized shocks used as a steering stabilizer does to quick lateral movement of the tie rod.

Sometimes, after repairing everything that can be repaired and replacing everything that can be replaced, Death Wobbles still exist because of design characteristics that you cannot change - then "masking" with Steering Dampers is totally acceptable.

I totally agree. This is what that engineer Turbostew said in the Quadvan Death Wobble thread:

"I don't believe you will ever get rid of the DW without changing some mass some where or dampener some where on the 05-0? Superduty setups. Lowering caster to 0 will do it but it will drive like $#&@. Sometimes changing backspacing on the wheels will change the "mass" adding more rational inertia about the kinkpin axis. Tires might do it. Vehicles with more angle from horizontal on the track bar or more bump steer (like the 05+ Fords) seem to be more prone to it. Just add more dampening and be done with it. Thats the way it works, you think you got it fixed, then at 2:00 AM on some road in BFE while you half asleep and there is a 500 ft drop-off the DW will hit you, screw that, if I learned anything in 15 years of engineering, it is dampening in mechanical systems is good thing!"

Finally, Bajasportsmobile and Ujoint what do you think of hydro steering on freeway speed passenger rigs?

sidetrak06: Thanks for making this thread. Thanks for the great pictures and video. Please keep posting your results and experience. The only thing I would say (as a non-engineer and not a suspension expert) your radius arms are stronger than your frame. So I would expect that your frame is repeatedly flexing and will eventually fail at the attachment point. Maybe post up some videos to see if I am right about frame flex there?

[sidetrak06]

Thanks for making this thread. Thanks for the great pictures and video. Please keep posting your results and experience. The only thing I would say (as a non-engineer and not a suspension expert) your radius arms are stronger than your frame. So I would expect that your frame is repeatedly flexing and will eventually fail at the attachment point. Maybe post up some videos to see if I am right about frame flex there?

When I get the van back I will mount the GoPro in another location behind the front axle so we can see what is happening at the radius arms. Should be interesting...

[BajaSportsmobile]

Originally Posted by sidetrak06

I have tried this approach since day 1, attempting to repair, replace and improve every component so that it would not fail or at least not for a while. Now I am dialing in the alignment and I have decided that I will not sacrifice tire wear by scrubbing with "toe-out" alignment just to prevent or hide the death wobble. After this I will be looking at the radius arms. If all else fails...dual steering shocks.

Does anyone see something that I am missing? Is there something else that needs to be modified or inspected?

From your original post: "I did not trust the alignment so I brought it to High Country Performance to check it out. They said the castor was maxed out at -3.7 deg (good), the camber was 0 deg (good) but it was toed out 0.25" (not good). This was done to hide the death wobble."

First, having toe out is not necessarily a bad thing, and 0.25" is not a lot on a 35" tire - you would not sacrifice tire wear "scrubbing" anymore than with comparable toe in.

Are you saying that the caster was -3.7 deg as in NEGITIVE CASTER? You do not want negative caster you want positive caster. Just want to clear that up...

[sidetrak06]

Originally Posted by BajaSportsmobile

Are you saying that the caster was -3.7 deg as in NEGITIVE CASTER? You do not want negative caster you want positive caster. Just want to clear that up...

Good catch, it is positive caster. I will change the post. I must have a lot of angles in my head.

[E350]

Oh yeah, one more thought. To my mind:

"Death Wobble" is merely "Bump Steer" with push back.

The dual opposing shocks used as a steering stabilizer dampen both the initial "push" and the resulting "push back."

[BajaSportsmobile]

Your response indicates that I am not making my case clear to you, or I was not understanding your original post.

Yes, the dual opposed steering dampers, do damp the rotational movement of the steering knuckles - whether attached directly to the knuckle or to the tie rod attached to the knuckle.

They are however damping (masking) the osculation - whatever the cause. It could be "fixed" with out dampers by correcting the cause - change wheels, tires, caster, steering inclination (something built into the axle and not adjustable) or some other design problem.

By the way dampen is to make something slightly wet by dampening it. When something is dampened it is made wet.

Damp - control, restrain, or reduce mechanical vibration.
Damped - is the past tense.
Damping - a decrease in the amplitude of an oscillation.
Damper - a device for reducing mechanical vibration or oscillation.
Knowing this, it is still easy to use the wrong word.

Originally Posted by E350

BajaSportmobile and Ujoint: You two are the people whom I wanted to draw out to critique my analysis of my cure for my DW. I write long posts so that I can put out my understanding for criticism so that I can learn from you guys. This is a subject matter that I have personal experience with and which I personally cured after the 4x4 converter failed to cure it despite work under warranty, $3,000 in extra work, and new tires all around (merely a temporary fix). See my responses in blue, below.

sidetrak06: Thanks for making this thread. Thanks for the great pictures and video. Please keep posting your results and experience. The only thing I would say (as a non-engineer and not a suspension expert) your radius arms are stronger than your frame. So I would expect that your frame is repeatedly flexing and will eventually fail at the attachment point. Maybe post up some videos to see if I am right about frame flex there?

[E350]

Dude, this was totally worth the price of admission...

Originally Posted by BajaSportsmobile

Yes, the dual opposed steering dampers, do damp the rotational movement of the steering knuckles - whether attached directly to the knuckle or to the tie rod attached to the knuckle.

They are however damping (masking) the osculation - whatever the cause. It could be "fixed" with out dampers by correcting the cause - change wheels, tires, caster, steering inclination (something built into the axle and not adjustable) or some other design problem. OK, then to cure DW (on a van which was originally designed as 2WD which has been lifted and converted to 4x4 with big tires, yadda yadda yadda) without damping, to my mind there are only two options available to the OP: 1) return the vehicle's suspension to the OEM 2WD as Ford designed it; or 2) have someone like yourself actually redesign the suspension in a fashion so as not to propogate bump steer (i.e., DW). From my experience with Salem Kroger as a 4x4 converter and apparently the experience of others (i.e., "Quadvan Death Wobble") when a rig is prone to DW, the normal 4x4 converter does not have the suspension redesign skills necessary to eliminate the DW by suspension design alone. Just sayin' based on my personal experience with my personal 4x4 converter...

By the way dampen is to make something slightly wet by dampening it. When something is dampened it is made wet.

Damp - control, restrain, or reduce mechanical vibration. I am embarrassed for sure, but happy to learn now (albiet after looking stupid in a number of long posts I made on this issue on various threads over the years... So, uh, thanks!).