Dave Wilson

I am about out of ideas, so I could really use some input. I have a '99 Cherokee with 168K miles, stock wheels, tires, and suspension. When I got it five years ago with 68K miles it had an unusual clunk, if I cranked the wheel all the way over and backed up it would clunk once, like something was loading up and then breaking free. While trying to find that I replaced the tie rod ends and track bar, with no luck.

Then a couple months ago I experienced death wobble for the first time. Wow. I found that the front shocks were completely worn out, so I replaced them and the DW went away. A couple weeks ago the DW came back bad. I changed the ball joints, and the DW got worse. Tonight I replaced one side of the control arm bushings because the girl at NAPA only ordered one side. I did the passenger side because I think that's where the clunk is coming from. The old bushings were in fine shape, the clunk is still there, and so is the DW. I'm not going to do the other side just yet.

I have looked all over the front suspension, and nothing seems loose or worn. I haven't had someone turn the wheel while I watch; will try that soon. I don't seem to be missing any wheel weights. The tires are about a year old, and don't have any cupping or unusual wear. The spring pad at the top of the front springs looks okay, although I haven't had it out. I even put a wrench on the steering box mounting bolts tonight, and they are tight. What could that clunk be? Is it a clue? Right now I'm thinking about track bar, then alignment and balance, and I don't know what after that.

Dave

diskman

Thinking of fixing my '99 also.. Try the trackbar ends, steering box and control arm bushings next. Jack one wheel off the ground and have someone slowly turn the steering wheel left and right. It's the only way to see if things are moving that shouldn't be.

My old ford F150 had a nasty wander till I had the wife turn the wheel while I looked. WOW. Many parts got replaced that weekend.

Dave Wilson

Tonight I rotated the tires front/back and side/side. The front end feels a little smoother, right up to where it starts violently shaking in a death wobble.

So then I got a new track bar and put it on. The old track bar looked fine, but there was a lot of advice on the internet saying that the track bar was a likely culprit. But I still have the death wobble.

I did find one page suggesting that the steering box might need adjusting. It does have an inch or two of play right at the steering wheel, right in the middle. I may try that.

Other than that, all I have left it an alignment. If I can survive until the weekend I'll take it into Sears, and see if that fixes it.

bryanboonern

I too have a death wobble and am about to tackle it as well. My 99 has about 175,000. It is also going to get a lift of some type...haven't decided which one yet...maybe Rough Country 3". I plan on replacing lower control arms, upper CR bushings, steering damper, shocks, springs, sway bar bushing, adjust steering box and maybe replace. Tie rod end on pitman arm (not sure the proper name for it). Probably will replace track bar as well. We'll see if that fixes it. Let me know what fixes yours.

4.3L XJ

That is probably your problem. Everything has to be tight or you can get DW even on a stock rig. Cheap fix any way.

Mike1998XJ

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
Steve
Here are a couple of Q&As I've received on another forum where I wrote about DW:

Can you explain why reducing caster helps on some vehicles? It doesn't seem like it should work, but it does.. and at other times more caster will cure it.
Basically, anything you do to get the front suspension back closer to original factory specs should help with DW. Remember, a lot of our vehicles were marginally stable from the factory, and when we lift them, change the steering, run huge tires, etc., we're making them even less stable. So, running the caster at whatever it was from the factory, along with making sure that the many other things affecting the front suspension are in good condition, will help greatly.

Unfortunately, there's no silver bullet for fixing DW, and what works for one person may not work for another. You have to consider the entire front suspension as a system and then make that system as stable as you can for the way you want to run it.

Pondering how too much caster can cause wobble, the more caster you have, the larger the vertical movement of the wheel will be, under steering input. More vertical movement = more influence that the weight of the rig can have on it, and particularly with large soft tires, that would be a fairly substantial, mostly undamped, weight hanging out there. Get it cycling, and it's not going to want to stop.

I really oughta crank down my caster a bit (front at 8 degrees) but no steering feedback = very difficult to get actual DW, so I've been lazy.
Scott, let's take it to the extreme to see why too much caster can make the suspension system unstable. Picture 90* of caster. The ball joints/kingpins would be horizontal, so when you turned the wheels they would turn top to bottom and not side to side. 90* is extreme, but the more + caster you have the more the wheels are turning top to bottom and less side to side. Besides getting pretty unstable (and VERY heavy steering feel) with much more than 10* or so, you also start scrubbing the tires pretty bad when turning with too much caster.


NOTE: For reference purposes, here is a diagram of what caster is. Positive caster is when the top of the tire "leans" toward the rear of the vehicle as depicted in the diagram.

http://www.familycar.com/classroom/I...ign_Caster.gif

Curing deathwobble is definetly a reality. Deathwobble isn’t similar to a wobble from an unbalanced tire. It is by far worse. When deathwobble hits you will know… it’s a violent shake form the front end that feels like the Jeep is about to fall apart. Usually when it happens the only thing you can do to stop it is slow down. The first steps to eliminate deathwobble should be a visual inspection of each component, check the bushings, tire balance and an alignment. There are some common things you must check anytime you lift your Jeep. Deathwobble is experienced mostly on lifter Jeeps, however it is not uncommon for someone without a lift to experience the dreaded DW. Listed below are a few things you can check.

Torque specs:

Item ........................................ Ft. lbs. ................... Nm

Lug nuts (1/2 X 20 w/ 60* cone) .... 85-115 .............. 115-150
All tie rod ends ............................ 55 ..................... 74
Steering (both ends) .................... 55 ..................... 74
Shock absorber upper nut .............. 16 ..................... 22
Shock absorber lower nuts ............. 17 ..................... 23
UCA frame end ............................. 66 ..................... 89
UCA axle end ............................... 55 ...................... 74
LCA frame end ............................. 85 ...................... 115
LCA axle end ............................... 85 ...................... 115
Track bar frame end ..................... 60 ...................... 81
Track bar axle end ....................... 40 ....................... 54
Track bar bracket bolts ................. 92 ....................... 125
Track bar bracket nut ................... 74 ....................... 100
Track bar bracket support bolts ...... 31 ....................... 42
Hub bolts (3) ............................... 75 ....................... 102
Hub- axle bolt .............................. 175 ..................... 237

Alingment specs (stock):

Angle ............. Preferred ........... Range ............. Max R/L diff.

Caster ............ +7.0* ........ +5.25* to +8.5* ......... 1.25*
Camber ........... -0.25* ....... -0.75* to +0.5 ........... 1.0*
Total Toe-in .... +0.25* ....... 0* to +0.45* ............. .05*
Thrust angle .... 0* to ± 0.15*



Check your Track Bar, play in this can cause the axle to shake.
1. Bushings - check to see that they are not worn. Looks for cracks, and excessive play)
2. Angles - this angle should be the same as your draglink. Use an angle finders you can get at sears to determine this, don’t just eye-ball it.
3. Bolts – Make sure all bolts are tightened down to spec (some lift components have a different torque spec then)

Check the Axle, your mounts may be worn
1. Check the axle mount. Here is a good write up on a wallowed out bolt hole
http://www.jeepin.com/features/trackbarfix/index.asp
2. Check your Universal joints, a binding or lose U-Joint can cause DW
3. On the frame end if you still use the conventional Tie Rod End or (TRE) make sure that there is no play in this, as play can cause DW.
4. Look/Check for worn/torn boots on ball joints/tie-rod ends.

Check your Tires
1. Out of balance tires can cause shaking in the front end, which can lead to deathwobble.
2. Make sure all of your lug nuts are tight, (Sounds elementary but it happens to the best of us)

Check your Frame
1. Small cracks in the frame can cause the steering box to feel loose, Shaking from DW can only make this worse. 33’s and larger should have some form of Steering box brace, or frame brace in.
2. If you have upgraded your frame mount, make sure its cranked down nice and tight. (best to use an impact gun)
3. A busted Frame Mount can cause play in the front end causing DW (Keep a watchful eye on the welds as welds in sheer can break over time.

Make sure you have a good alignment
1. After you get an alignment done, have them print out the numbers for you. An XJ should have a 7* positive caster angle. A lifted XJ can’t always have that high of a number because the pinion would become out of alignment with the front driveshaft. Pinion angle takes precedence over caster.
2. Make you sure you go to a place that will adjust the caster if necessary (either by shims in the frame side of the LCAs, or adjustable LCAs).

The more adjustable parts the easier it is to tune in your suspension.
1. Adjustable Track Bar
2. Adjustable Upper and Lower Control Arms (upper ones above 4” of lift). Not only are they adjustable, but they are stronger.


Things to remember:
1. A Steering Stabilizer (SS) is not a quick fix for DW.

Entire list of everything that can cause deathwobble:
-Front tires out of balance
-Front alignment out of spec
-Loose track bar
-Worn track bar bushings
-Worn track bar end
-Need adjustable track bar
-Bad bushings/joints in control arms
-Worn/damaged steering stabilizer
-Worn/damaged shocks
-Worn/damaged tie rod end
-Bad U Joint
-Bad ball joint
-Loose frame mount
-Steering box looseness
-Need drop pitman arm
-Driveshaft(s) not balanced
-Bad front hub assembly

ThumperK15

I cured mine by messin with the tires. One was turned out more and at that certain speed they would fight each other causeing DW.

SpitFire

My brain hurts after reading that, but dang if that isn't helpful as hell. Thanks for posting it!

smitysjeep4x4

X10000000000000000000000000000000000000000000000 this helped me cure mine thanks alot mike

I would do the alignment that fixed mine

Dave Wilson

it's fixed. the alignment did it. i can still feel a slight wobble between 50 and 60, where it feels like it wants to go into full convulsions, but can't quite get up the energy. but at least it's driveable now. i'll try replacing the steering dampener to see if that smoothes out the vibrations.

thanks for all the input and suggestions.

HoopiesWyf

*phew* so nice to know this is something commonplace, and not because of something I did voluntarily due to my driving. LOL Thanks Mike for the tips...will take my baby to get an alignment...maybe then it won't get the "doog doog doog" DW. LOL

whiteknight98z28

At first I thought you had to be a Doctor or NASA Engineer to understand this but it is very useful I also have the DW didn't have a clue what to start with but after reading this I do now mine is the 2nd DW only happens when I hit a pothole or something that jars the jeep and then its hold on to your pants. So thanks alot

stan'sredxj

Mine was DW #1. turned out to be a combo of alignment and pitman arm...I had to get a new drop pitman arm. Good luck

semperfi96

Woow, I choose to read this o the crapper instead of my playbow, and still got a woody!!!!!!!!! , thanks for the repost, this is great info

Dave Wilson

Well, unfortunately my DW is back. Now it seems to be triggered by touching the brakes around 50-60, although I can feel it trying to start before that. I replaced pads and rotors at the time of my first post here, about 8K miles ago. When the DW came back I torqued the lug nuts to make sure I hadn't warped the rotors by using an impact wrench, but it didn't help.

So within the last 10K miles I have done:

• front shocks
• sway bar bushings
• ball joints
• upper and lower control arm bushings
• track bar
• tires
• pads and rotors
• alignment
• checked every nut and bolt I could find for looseness

This is on a stock '99 XJ. Because everything in the front end is new, yet the DW came back, I'm thinking mike1998xj's suggestion of broken frame mount might be the answer. I bet that would also explain the mysterious clunk.

So how do I check that? I have looked all over the front end for cracks, but haven't seen anything. I got to admit I don't even know where the frame mounts are. I guess it's time to check the manual.

Dave