VenomHP

Hey guys, Im about to put the cherokee in storage for the next few years unless theres a different solution... Right now my wifes jeep 98XJ has a 3.5" basic lift with 1.5" spacers for the bumper. About a year and a half ago we invested almost 2k in new tires, ball joints, tie rods, after market control arms, drag link and labor to solve the death wobble. Its got maybe 2500 miles on it since then and its starting to come back. Im thinking of either throwing money at it again redoing the lift kit with a 4.5, and fixing whatever is worn out (needs other work as well) or putting it in storage back in TX and buying a different vehicle for her.

I dont mind putting money towards it again, but I dont want this problem to come back in another 2500 miles, thats rediculous! what lift kits are not giving you guys problems?

heres a pic of the jeep now

mike37

try swaping the back tires to the front

mike37

I would suggest any one with the DW do a tie rod conversion
like the one Rusty's has
not saying his is good or bad
but the stock setup will make the DWs worse cus of the way its designed
the soled bar will help big time

http://rustysoffroad.com/mm5/merchant.mvc?Screen=PROD&Store_Code=rustys&Product _Code=RS-SC250-UV&Category_Code=ste

VenomHP

we just rotated the tires and its still there...

VenomHP

the drag link has the hiem joints on it and is new so I dont think its worn out yet

mike37

is it still the Y link or a solid cross bar from hub to hub
if its still the Y link a chang would be good

a tire rotation may have left one front tire in front

mike37

never mind

VenomHP

Im pretty sure the steering is still set up stock so I guess the y style, and the tire rotation was just front to back, has that tie rod kit been proven to stop the DW?

Mike1998XJ

Read this. It may help.
Mike
Death Wobble explained…
Here's an engineering description of DW. I get tired of seeing people guessing at what's causing their DW, so here goes. Hope it helps someone.

First, you've got to realize that the front suspensions on our vehicles were marginally stable, at best, from the factory. DW is a fundamental dynamic response mode of the entire front end...as a system. Lift and larger tires change (increase) the 'gain' associated with what becomes (or even starts out as) a marginally stable dynamic system. The damping factor (lambda) is also affected by larger tires...it decreases as a function of sidewall height/thickness ratio. Hysteresis in any control path (loose tie rod, steering box, track bar bushing) reduces the ultimate stability margin further. The fundamental frequency of DW is determined by the superposition principle where all springs involved are resolved (frame, tire resilience, hub bending, bushing deflection, etc, etc.) into one global spring constant, and all damping factors associated with friction, elastic elements, viscous damping (steering damper and shocks) are resolved into one damping factor. The natural frequency, damped natural frequency, and damping coefficient are then known. Now, if the system is overdamped and the gain is low...no problems...no oscillation. Increase the gain without increasing the damping and you go toward the critically damped, and beyond, specturm of responses. Critically damped means that DW would only 'hint' at being there, but would die out on its own without going totally unstable. This is also known as a decaying response.

Once the system goes beyond critically damped, any excitation, be it an unbalanced tire, a bent wheel, bumps in the road, etc. can set it off and the response will not decay...it will grow in amplitude, quite quickly in some cases, and may be limited only be physical non-linearities like hard stops...or breakage. That's classic Death Wobble.

A truck suspension is designed to stay in the overdamped to critically damped range. That is generally why a truck rides "rough". A Cadillac, on the other hand, is designed to stay in the undersprung range. It just "floats" down the road. Any change in the basic design parameters that affect the gain (e.g., lift, tire size, wheel backspacing, etc.), damping (tire size, steering damper, steering box condition), and hysteresis (any wear point that creates any slop) can push it over the edge and create DW. ANY ONE OR TWO of the factors discussed can do that...which is why everybody then thinks that whatever problem THEY found and fixed is the cause of all DW; it is not. It is plain and simply a marginally stable system in its original form that is easily made unstable by any of the myriad causes discussed already.

If your front end is loose (bushings, bearings, etc.) then you have a situation where your stiffness is removed and any jarring sensation (potholes, unbalanced tires, misaligned wheels, etc.) will cause the suspension to go crazy. It is no longer functioning where it is designed. On the other hand, your suspension could be very tight but an imbalanced tire would be spinning at just the right speed to throw the suspension into a unstable situation.

So unfortunately there isn't only one root cause to the problem of DW. The underlying problem is instability in the front suspension, the root causes can be a multitude of things ranging from bad/loose bushings, to loose bearings, to caster angles, to imbalanced tires, etc.

OKAY, HERE'S THE REALLY USEFUL INFO:

A steering damper only hides (maybe) the effect; it does nothing to fix the root cause.

There are two types of DW. The first typically is speed related. Whenever you reach a certain speed, bam, you get DW, no matter what. This is a vibration/oscillation issue. Look into tire balance, alignment, steering joints, missing bushings (totally shot), loose steering box (either loose bolts or worn internals), etc.

The second is an impact initiated DW. For example, hitting a pothole above a certain speed will start DW. This is more likely a bushings, loosening mounts, flexing components, etc. issue. Basically, something is tight enough that in general straight driving, it is ok, but give it an impact force, whatever is getting loose starts sliding, rebounds and starts going nuts.

Here is how you can tell if the issue is steering related or trackbar related. You are gonna need some ***** for this, but stick with me. Once you have played around with the DW awhile you find you can control it a bit by feathering the brakes. So go find a straight, deserted, bumpy road. Get the truck up to speed and get the DW going. You had it happen a few times, you have already been frantically avoiding potholes, so now go find one, quit whining. At this point, the truck is somewhat violently shaking, and you can keep enough control using the brakes to keep it on the road. Roll down the window and stick your head out and look at the front tire. What is it doing?

1. The front of the tire and the back of the tire are moving approximately the same amount side to side. In this case, the axle is stationary, and the wheel is pivoting on the ball joint during the oscillation. Therefore the problem is likely in the steering. Something in the steering has enough give to allow the movement.

2. The back of the tire is moving MORE than the front of the tire in the side-to-side movement. In this case, the knuckle is pivoting on the steering links, and allowing the axle to move back and forth under the vehicle. The problem here is most likely in the trackbar system.

This doesn't really answer a question about what's causing YOUR DW, but it should give you something to think about in your search for the root cause(s). I'd check the trac bar bushings, make sure your wheel bearings are in spec, make sure your tires are balanced, make sure your alignment is in spec - especially caster, make sure your ball joints & TREs are tight, see if you have play in your steering box, etc.

Everybody got all that? ;D

EndlessMtnFab

You copied that from another thread



Joe

Mike1998XJ

yes, I posted it on another thread and as I said there it is not my work... Have you used the information in it yet?
Mike

EndlessMtnFab

I know you did ... I was just funning you.



Why would I use it?



Joe

Mike1998XJ

You haven't stuck your head out the window to see the characteristics displayed by your tires during a death wobble experience? Or aren't they wobbling that bad yet again?
Mike

EndlessMtnFab

I've yet to have a death wobble issue ... you confusing me with someone else?


I have only had a wobble on my own Jeep one time in 17 years and I knew why I had it (swapped in too long LCAs because I sold the set that was on the jeep before). Shortened the arms the next night and all was well with the world.


Bump steer is a more aggravating issue for me to diagnosis for my customers. Wobble I can usually nail without even driving it.



Joe

Mike1998XJ

Wow, you must really understand DW then...
Mike