Diagnosing Death Wobble and Fixing Non-DW Shimmies and Wobbles (TJ Version) - JeepForum.com
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post #1 of 380 Old 04-25-2014, 04:10 PM Thread Starter
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Diagnosing Death Wobble and Fixing Non-DW Shimmies and Wobbles (TJ Version)

Speed dependent, easily repeatable, always-happens-at-a-given-speed wobbles and shimmies are nearly always tire or wheel related.

Death wobble is a random, violent oscillation of the front end and steering system that requires a trigger (like a bump, pothole, bridge expansion joints, or severely out of balance tires), and it requires coming almost to a complete stop to cease the violent oscillations.

Death wobble is violent enough that even a few episodes will damage ball joints, tie-rod and drag link ends, front upper axle side control arm bushings, unit bearings, and most importantly, front trackbar bushings, ends, and bracket bolt holes.

Nonetheless, diagnosing non-death wobble shimmies and wobble can be similar to diagnosing and fixing sources of death wobble.



Death Wobble doesn't have to be a mystery.
It is usually caused by loose bolts, imperfect tire balance, damaged components, or improper
installation.



Look at the picture below and follow along:


First, the tie rod (yellow) has ends that attach to a knuckle on the driver side and the drag link on the passenger side. As you could imagine, if either ends of the tie rod were broken or bad, that could be a culprit for a shimmy (not Death Wobble). A common place to damage the tie rod is on the driver's side at the adjusting collar (not in the picture). That collar/sleeve allows the width of the tie rod to be expanded or contracted. There are threads on that end that can be damaged, causing play on that driver's side and allow an up and down, or circular play movement. Again, this would cause a shimmy, not Death Wobble.

Next, look at the drag link. On one end, it attaches to the pitman arm (light green), that attaches to the steering gear box. On the other end, the drag link attaches to the passenger side knuckle. When you turn your steering wheel, a shaft turns that goes to the steering gear box. The steering gear box turns the pitman arm, and the pitman arm pushes or pulls the drag link, which pushes or pulls the knuckle. Your steering wheel is straitened by loosening the two nuts on the sleeve/turnbuckle on the drag link and rotating the sleeve/turnbuckle to lengthen or contract the length of the drag link. If either end of the drag link is damaged, this would cause a wobble or shimmy, sometimes, a really bad wobble, but I wouldn't call it Death Wobble.

Next, look at the trackbar (aqua). It attaches to a bracket on the frame on the driver's side and to the axle on the passenger side. The purpose of the trackbar is to center the axle on the frame. With the axle centered on the frame, it provides some resistance to the steering system to allow you to turn. If there was no trackbar and you turned the steering, the whole front frame would shift. As a result, there is significant force applied to the trackbar in driving and steering.

Now, imagine that the bolt and end that holds the trackbar are loose in their bolt holes, or that the axle side bolt holes are wallowed out (oval) and the end at the frame side is damaged, or that the bushings at the axle side trackbar end is damaged, or that the bracket at the axle side has come loose because the weld has broken/cracked, or that the axle side bushing is all twisted up because the rig has been lifted without the installer loosening the bolt and then retightened them at the new ride height and the bracket has pinched the bolt sleeve in the bushing at a different ride height--twisting the sleeve away from the bushing. All these things would allow play in the front trackbar. When you steer or go around a corner, these loose or broken things would allow the axle to shake or slide side to side. If you hit a bump in the road, it could knock the trackbar towards the driver's side. Then, the rest of the suspension (springs, etc.) would try to bring the trackbar back to the passenger side. If you were going at any sort of speed, you could develop a kind of harmonic resonance as the axle more and more violently slide/rocked/shaked from side to side. It would feel like your whole front end was being voilently torn apart. You would have to bring your vehicle to a complete standstill to stop the harmonic resonance. This is Death Wobble.

Also, look at the picture of how the frame side of the trackbar has something similar to a tie rod end. When the suspension droops in a TJ or XJ, the design of the frame side ends binds the end and can damage or break the end--leading to the scenario described above.

Even one incident of violent Death Wobble related to the front trackbar can cause significant damage. The voilent harmonic resonance of the back and forth shaking is more than the trackbar bushings, trackbar frame side end, bracket bolt holes, and brackets and welds are designed to handle. A severe Death Wobble occurance can crack or break the welds on the axle side trackbar bracket, or the bolt can wallow out the bolt hole in the bracket, or the bushing can be permanently damaged.

This is the most common source of Death Wobble because inexperienced installers either do not remove the bolt from the trackbar when they install a lift--leaving the bushing pinched in the bracket and bound up, or they do not properly torque the bolts after the lift has been installed with the tires on and the full weight of the vehicle on the ground at ride height, or (maybe the most common) they do not retorque the trackbar bolts after the first 50 miles, after every heavy wheeling trip, and at every oil change interval.

Next, look at the lower control arms (orange) and the upper control arms (purple). In the picture, they are stock arms. The stock control arms have a rubber bushing at each end. When the control arms are properly torqued, the bushing is somewhat pinched in the mounting brackets on the axle and the frame. Sometimes, an installer will make the mistake of not loosening the bolts for the control arms when they install a lift. What happens sometimes is they really bind up the bushings because they are pinched/sandwiched at stock ride height, but then forced to the new lifted ride height. These bound up bushings can cause weird handling, bushing failure, and lead to Death Wobble. The proper way is to loosen the bolts, install the lift, reinstall the wheels so the suspension and jeep are at the new ride height, rock the vehicle/suspension back and forth and side to side, then re-torque the bolts to spec, then after 50 miles re-torque them to spec, then after every oil change or very heavy wheeling trip re-torque them to spec.

Improperly balanced tires, too much air in tires, bent wheels, improperly installed wheel spacers, bad tires (with separated plys), and poor alignment specs (caster, camber, and not enough toe-in) can cause wobbles and shimmies that lead to Death Wobble. However, these precipitate Death Wobble, but they are not the cause of Death Wobble.
Although not specifically identified in the picture, the ball joints that are at the top and bottom of each knuckle where it attaches to the axle C can go bad. Bad ball joints can cause shimmies, wobbles, but usually not full on Death Wobble.

The swaybar links (red) have bolts that can work themselves loose. This also can lead to bad wobbles.

Next, allthough not identified in the picture, the unit bearings can go bad and be a cause of shimmy and wobble, but not Death Wobble.

Hope this helps--assuming you read it all.

Death Wobble is no mystery.

The reason that the steering stabilizer masks it is that it can absorb some of the side to side voilent harmonics of a loose trackbar or damaged mounts. However, this masking is dangerous because it will not prevent the eventual failure of trackbar bracket welds and bolt holes from trackbar Death Wobble.

It is extremely important to immediately diagnose and fix Death Wobble.

Even one episode of DW can damage other components.

Multiple episodes of DW are almost guaranteed to damage other components.






Multiple episodes will often damage your:
  • ball joints
  • tie rod ends--including the adjusting sleeve end on the driver side
  • trackbar bushings
  • trackbar bracket bolt holes
  • steering sector shaft (where the pitman arm attaches to the steering box)
  • steering stabilizer
  • front lower control arm bracket bolt holes
  • unit bearings
  • trackbar bracket welds
  • drag link ends
There are many, many examples of jeepers who with 5-6 episodes of trackbar related DW even on an a stock jeep have ended up "chasing their tails" for many, many months. It is not uncommon for people to end up replacing almost everything in the above list--sometimes more than once chasing sources of DW and non-DW wobbles and shimmies.




Without repairing/replacing everything that was damaged at once, the remaining damaged components continued to cause DW problems, further damaging the remaining components.


This is Death Wobble on a JK (and the guy is unwise for repeating it on purpose):




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post #2 of 380 Old 04-25-2014, 04:11 PM Thread Starter
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DIAGNOSIS CHECKLIST

  1. Assuming your tire psi is appropriate for the service description/load range of the tire, given the weight of your rig and width of your wheels (often about 26-30 psi for a TJ), and assuming your tires/wheels have been balanced and rotated to make sure the wobble doesn't move with the rotation, and that your tire tread wear is not feathered or cupped, move on to the next steps.
  2. Remove the steering stabilizer for the inspection because it will mask/buffer the following items if left attached.
  3. (Dry Steering Test) Have someone turn the engine on and turn the steering wheel with short, sharp, quick back and forth turns of the steering wheel between the 9 o'clock and 3 o'clock positions while you listen and feel the tie rod, drag link, sector shaft, trackbar, bracket welds, and the component ends for clunks, knocks, worn parts/ends, etc. (If your tires are not too large, sometimes it is easier to hear clunks if you do this step with the engine not running, but with the key in the ignition.)
  4. (Dry Steering Test continued) Then, do the same thing but slowly from full lock to full lock while I visually, manually (with my hands on the components), and auditorily inspect for flexing components--trackbar, drag link, tie-rod, brackets, steering box, etc. Look to make sure that the steering stops on the knuckles stop the full lock turn before the steering box stops turning the sector shaft and pitman arm.
  5. Then, because the Dry Steering Test may have not exposed ovaled bolt holes, separated bushings, or cracked bracket welds, I would remove the front trackbar to inspect the axle bracket bolt holes for ovaling and inspect the trackbar bushings for separation or cracking with a long screw driver through the bolt sleeve and the trackbar in a vise to leverage against the bushing in all directions. I would also inspect the frame side bracket for damage and the frame side end of the trackbar for up and down play using a channel lock pliers. If all is good, I would reinstall the trackbar with the tires on the ground at ride height to 55 lbs at the axle side and 65 lbs at the frame side.
  6. Then, I would inspect the drag link end joints by using a large channel lock pliers that gave me enough leverage to check for up-and-down play in the drag link ends. There should not be any meaningful up and down play. If there is, the ends should be replaced, or a new drag link with heavy duty joints should be installed. After, I would check the torque of the drag link ends. Taller lifts magnify the problems of bad drag link ends.
  7. Then, I would inspect the tie rod ends with the channel lock pliers for up-and-down and in-and-out movement. There should be no meaningful play. There should only be rotational movement in the joint ends.
  8. Then, I would put the front axle on jack stands with the tires about 2" off the ground and check the front ball joints by using a long pry bar as a lever under the front tires to lift them up to inspect for up and down play in the lower ball joints. There shouldn't be more than maybe 1-2 mm.
  9. Then, I would use the prybar/lever against the frame, or usually, just my hands to yank in and out on the top of the tire to inspect for lateral movement of the top ball joints. There shouldn't be any. If you have a lighter tire/wheel combo, you can easily do this by hand.
  10. Then, I would remove the front tires/wheels and remove the front tie rod--one knuckle at a time. Then with a large wrench or vice grips, I would inspect the end for side to side play. Then I would reinstall the end and torque to spec (20 ft. lbs.) and repeat on the other side.
  11. Then, I would remove the brake calipers and brake disks to inspect the unitbearings for play.
  12. Then, I would reinstall the discs, brake calipers, and tires/wheels and set the axle back on the ground.
  13. Then, I would support, but not lift, the front axle with a floor jack and loosen the front lower control arm bolts. One at a time, I would drop the lower control arms to inspect the bolt holes and bushings (similar to with the trackbar), reinstall without torquing, and do the next one. Afterwards, remove the floor jack so the suspension is at ride height, vigorously rock the vehicle side-to-side and front-and-back, then torque to spec. (LCAs frame side 130 ft lbs, LCAs axle side 85 ft lbs, and upper CAs 55 ft lbs.
  14. Next, I would inspect the sector shaft that comes out of the steering box for cracking or twisting of the splines.
  15. Then, I would take a test drive without the steering stablizer to feel for any wobbles.
  16. Finally, I would reinstall the steering stablizer or spring $40 for a heavy duty steering stablizer.
If this front end inspection does not diagnose and/or solve it, then I would move to an alignment.
  1. I would use adjustable lower front control arms to set my caster spec between 4 and 5 degrees--with a cross caster that has less on the driver side than the passenger side. I would personally not do more or less, with a target around 4.5-4.7 degrees caster.
  2. If my camber is out of spec, but it is not due to failed ball joints, I would install offset ball joints to get my camber in spec.
  3. I would set my toe-in to spec on the machine--which is about a 1/16" to 1/8" toe-in, depending on tire size.
  4. If my front to rear thrust angle alignment is off, I would install rear lower adjustable control arms to fix this.
With all this, I highly doubt you do not find the source.


The last ditch thing if there is a non-DW, speed dependent range wobble, I would borrow a different set of wheels and tires to see if it changes, and I would try driving it with no front driveshaft to see if that changes anything.

Although it is always a good idea to inspect your axle shaft u-joints, they will not cause DW.



The most common sources of full on DW are:
  • Improperly torqued trackbar bolts
  • Damaged trackbar and control arm bushings because bolts were torqued on a car lift or while the vehicle was not at ride height with the tires on the ground. When you torque trackbar and control arm bolts, the bracket pinches the bolt sleeve in the bushing, as well as the bushing itself. If this is at a geometry other than actual ride height, the bushings are twisted/bound/pre-loaded, and they will eventually fail/separate/etc. If you have a flex joint end, this does not apply for that end.
  • Ovaled out trackbar bracket holes due to DW episodes from loose bolts.


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post #3 of 380 Old 04-25-2014, 04:12 PM Thread Starter
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Although not a TJ, here is a link to abreviated JK diagnosis videos:

The videos are kind of long at 18-19 minutes each. Hopefully, they are thorough enough to help.




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post #4 of 380 Old 04-25-2014, 06:08 PM
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While I do appreciate the effort you've put into this, the one challenge I will make to your claim about DW not being a mystery is simply not true.

A simple experiment I did inadvertently once proved to me that while I am very astute at finding and fixing DW, I'll never fully understand it and neither will anyone else.

What would happen if you loosened all the bolts that hold the steering gear to the frame to less than finger tight or about 1/8" away from being tight enough to touch the in frame bolt sleeves? Would that induce DW?

Why would simply installing a MML cause repeated instances of DW?

Why do JK owners believe that bolt diameter has anything to do with clamping force?

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post #5 of 380 Old 04-25-2014, 06:36 PM
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Quote:
Originally Posted by mrblaine
While I do appreciate the effort you've put into this, the one challenge I will make to your claim about DW not being a mystery is simply not true. A simple experiment I did inadvertently once proved to me that while I am very astute at finding and fixing DW, I'll never fully understand it and neither will anyone else. What would happen if you loosened all the bolts that hold the steering gear to the frame to less than finger tight or about 1/8" away from being tight enough to touch the in frame bolt sleeves? Would that induce DW? Why would simply installing a MML cause repeated instances of DW? Why do JK owners believe that bolt diameter has anything to do with clamping force?
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post #6 of 380 Old 04-25-2014, 06:42 PM
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Quote:
Originally Posted by mrblaine View Post
While I do appreciate the effort you've put into this, the one challenge I will make to your claim about DW not being a mystery is simply not true.

A simple experiment I did inadvertently once proved to me that while I am very astute at finding and fixing DW, I'll never fully understand it and neither will anyone else.

What would happen if you loosened all the bolts that hold the steering gear to the frame to less than finger tight or about 1/8" away from being tight enough to touch the in frame bolt sleeves? Would that induce DW?

Why would simply installing a MML cause repeated instances of DW?

Why do JK owners believe that bolt diameter has anything to do with clamping force?
I'm a little shocked to hear that adding a MML could induce death wobble. Being that you are a very credible source I will have to believe you.
I picture two things happening when adding a MML; One, the drive shaft angle would change and two, you are raising the center of gravity of the engine (in comparison to the frame) and shifting a little more weight to the rear.
Have I missed anything else going on? Any ideas what causes death wobble from installing a MML? Does (or can) an improper pinion angle up front induce death wobble?
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post #7 of 380 Old 04-25-2014, 08:13 PM
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Probably related to vibration resonance/coupled harmonics? For a MML to cause DW, I'd theorize a MML had an effect on the vibrations the engine created and fell into resonance with another vibration up front in the suspension somewhere. The two then fed off each other and amplified to create DW.

Look up Partnair Flight 394. It broke apart in mid flight due to what you could consider airplane death wobble. The cause? Basically, it was a broken mount on its auxiliary power unit (generator) in the tail of the aircraft and weakened bolts (non-aircraft grade) that held the vertical stabilizer to the fuselage. The two created vibrations that resonated together and vibrated the plane apart.
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post #8 of 380 Old 04-25-2014, 09:16 PM
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Quote:
Originally Posted by Dave02TJ View Post
I'm a little shocked to hear that adding a MML could induce death wobble. Being that you are a very credible source I will have to believe you.
I picture two things happening when adding a MML; One, the drive shaft angle would change and two, you are raising the center of gravity of the engine (in comparison to the frame) and shifting a little more weight to the rear.
Have I missed anything else going on? Any ideas what causes death wobble from installing a MML? Does (or can) an improper pinion angle up front induce death wobble?
Anything that changes the stiffness of the supporting members will also change the resonant frequency is the only thing I can come up with and even then I struggle to get my head around it.

There have been several instances on here where the only thing done was to install the MML and then DW became prevalent.

I followed the threads intently looking for the telltale clue that something else was done and just not mentioned but that wasn't the case any of the times.

I know from conversations with the folks at Chrysler that DW is insidious and on one instance on the development of a new model, the simple act of adding 3/4" of lift with a different set of springs was enough to induce DW and the way it was cured was to make new control arm bushings with a slightly higher durometer.

No one answered with their thoughts on the loose steering gear?

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post #9 of 380 Old 04-25-2014, 09:20 PM
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The more you learn, the more you realize how little you know.
I'm a pretty cut and dried cause and effect guy. I like to prove and disprove theories and issues with simple AB substitutions. Or, take what is said to be the cause of the problem, recreate it and see if it does have the desired effect.

At the end of the day, I'm running 40" unbalanced tires at speed over rough terrain and I have not had a single instance of DW. Why is that if it's so important to take the tires out of the equation?

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post #10 of 380 Old 04-25-2014, 09:28 PM
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Quote:
Originally Posted by mrblaine View Post

No one answered with their thoughts on the loose steering gear?
I'd say if the bolts were that loose, it wouldn't cause DW. You'd be darting all over the place for sure until the bolts let go, but it wouldn't cause enough "vibration" to create a DW oscillation vs if it was a little more tight?
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post #11 of 380 Old 04-25-2014, 10:01 PM
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I'd say if the bolts were that loose, it wouldn't cause DW. You'd be darting all over the place for sure until the bolts let go, but it wouldn't cause enough "vibration" to create a DW oscillation vs if it was a little more tight?
They were loose enough to cause unsteady steering. I finger tightened them to touching, steering tightened up considerably with NO DW, tightened them all the way down and steering went back to normal.

That taught me that the issue is more related to inability to control the inherent precession that tires have more than anything else. Speaking of which, look up precession, it is absolutely fascinating.

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post #12 of 380 Old 04-25-2014, 10:26 PM Thread Starter
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Quote:
Originally Posted by mrblaine
While I do appreciate the effort you've put into this, the one challenge I will make to your claim about DW not being a mystery is simply not true. A simple experiment I did inadvertently once proved to me that while I am very astute at finding and fixing DW, I'll never fully understand it and neither will anyone else. What would happen if you loosened all the bolts that hold the steering gear to the frame to less than finger tight or about 1/8" away from being tight enough to touch the in frame bolt sleeves? Would that induce DW? Why would simply installing a MML cause repeated instances of DW? Why do JK owners believe that bolt diameter has anything to do with clamping force?
Blaine,

You'll forget more about jeeps than I'll ever know, but I'll do my best to answer your questions.

First, I'd clarify that I'm using a definition of DW that is randomly triggered by either road imperfections or extremely unbalanced tires. The oscillations are so violent that they require almost a complete stop to cease them. You can't drive out of the oscillations. Continued driving with repeated DW episodes destroys ball joints, trackbar bushings, drag link and tie rod ends, ovals trackbar bracket holes (or rips the bracket off the axle), unit bearings, ball joints, front upper axle side control arm bushings, etc.

So, the definition I'm using for DW is not easily repeatable without some sort of trigger that starts the oscillations, it's not speed dependent, it can't can be driven out of by going faster, etc.

So, to answer your first question, if you loosen your drag link and tie rod ends, your trackbar end and bolt, your upper and lower axle and frame side control arm bolts, loosen your swaybar links, and do it on a rig with worn ball joints and unit bearings, you wouldn't experience full on DW without a trigger. You'd need to drive it diagonally across a railroad crossing, bridge expansion joints, uneven potholes on a rough road, or some other terrain that triggers the oscillations.

A MML would not be the source of DW. It would be coincidence that DW reveals itself after a MML.

What I have seen as the common sources starts with loose trackbar bolts, combined with control arm bushings that are twisted/pre-loaded/binding to the wrong ride height because the bolts were not loosened for a lift install and only torqued after the full weight of the vehicle is on the ground at the new ride height.

The steering stabilizer masks the pre-loaded control arm bushings and the loose trackbar bolt(s) for a while, but not before the bracket bolt holes get ovaled, the drag link end gets worn, possibly the lower ball joints are worn, and the trackbar bushings are damaged. Then, they typical shop installs a new steering stabilizer instead of fixes the source(s), and more damage ensues.

The issue with the JKs is that when the smaller stock bolts loosen up from 125 ft lbs, the DW ovals the holes and scores the bracket enough that simply torquing the bolts again to 125 ft lbs isn't enough clamping force to stop further problems.

A JK owner with stock bolts who routinely torques the front trackbar bolts at every oil change interval shouldn't ever have a problem. The stock bolt is a course thread bolt and fully threaded. It doesn't hold torque as well as a fine thread bolt. A slightly larger, 9/16", partially threaded, fine thread bolt won't score the bushing bolt sleeve, holds torque better, and is less likely to oval the bracket bolt hole.

However, in the end, the primary value in the bolt swap is behavioral because JK owners are more likely to understand their front end and routinely torque their bolts at regular intervals with the swap.

It has nothing to do with clamping force.

Additionally, few lift installers take the time to loosen all bolts during an install. As a result, they cause premature bushing failure/separation because of the binding/pre-loading/twisting at the wrong ride height. With the bolt swap, people do it with their rig on the ground at current ride height. So, the bushings are pinched between the brackets in neutral position.

But that is regarding JKs.


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post #13 of 380 Old 04-25-2014, 10:39 PM
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Quote:
Originally Posted by mrblaine
...
No one answered with their thoughts on the loose steering gear?
So I don't know that area of the frame very well. Is the gear mounted to a really rigid portion of the frame. Maybe it isn't a soft enough (probably a poor choice of words, kinda mean flexy) portion of of the frame to let an oscillation to begin? Just shooting from the hip, just kind of entered my head so why not throw it out there. Could also be that or a combination of its (that corner of the frame) location is much better isolated from the axle (springy) side of the equation?
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post #14 of 380 Old 04-25-2014, 10:48 PM
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So I don't know that area of the frame very well. Is the gear mounted to a really rigid portion of the frame. Maybe it isn't a soft enough (probably a poor choice of words, kinda mean flexy) portion of of the frame to let an oscillation to begin? Just shooting from the hip, just kind of entered my head so why not throw it out there. Could also be that or a combination of its (that corner of the frame) location is much better isolated from the axle (springy) side of the equation?
On my phone don't know how to edit, so thought I'd add something. So the bar going to the steering gear is the last link in the steering and the loose bolts kind of are maybe kind of a solid dampened (yet loose) connection. Or more likely the mass of the gear could be acting as kind of an anchor? Wondering if a person wast to repeat your loose bolt test with some rubber isolators maybe DW could be induced?
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post #15 of 380 Old 04-25-2014, 11:07 PM Thread Starter
planman
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Originally Posted by J03_TJ
On my phone don't know how to edit, so thought I'd add something. So the bar going to the steering gear is the last link in the steering and the loose bolts kind of are maybe kind of a solid dampened (yet loose) connection. Or more likely the mass of the gear could be acting as kind of an anchor? Wondering if a person wast to repeat your loose bolt test with some rubber isolators maybe DW could be induced?
It would be induced simply by driving through a series of uneven potholes, bridge expansion joints, diagonally over a railroad crossing, or something else that started the oscillations between the trackbar ends, drag link or tie rod ends, worn ball joints, etc, combined with the interactions of the coil springs and control arms pushing/sliding and pulling the front end back towards center under the jeep.


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