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Old October 31st, 2011, 11:53 AM
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Chris Davis
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Death Wobble Eradication

Death Wobbles. They suck, they are scary and they are dangerous. This was my first case of this disturbing affliction but I am well aware of the concept, the theory, and mechanics involved so I thought that I would share my situation for others with this problem.

Death wobbles are when your front tires develop an oscillation from side to side—basically a massive vibration—that hits harmonics at certain speeds causing a violent shake/shimmy of your steering that. It translates through your drive system which you can feel in your steering wheel which also rotates side to side. It is caused by slack or looseness somewhere in your steering system so there are many causes. Your steering damper is not one of the causes (although they can sometimes help mask the problem for some trucks) as their role is to dampen large movements in your steering system, not the small oscillations. I have driven my truck without a steering damper and without death wobbles, so don’t waste your time swapping your out to solve this problem.

To the best of my knowledge, there are 5 main things to check to eliminate DW’s. They are your alignment, tire balance, pan hard rod bushings, tie rod ends, and swivel pin preload. When I drove my car after sitting for 9 months, my DW’s (which I didn’t previously have) caught me by surprise. My alignment was fine but I recalled that I rotated my tires, so the first thing I did was take them to Costco ($4 for balancing per tire, 255/85/16) which they said was a major PITA and were way out of balance. Next test drive confirmed that this was a significant cause, but at 55mph, the DW’s still came back (less, but still scary). Next on the list, pan hard rod and tie rod ends. All tie rod ends in my case were very good, no slop at all, but looking at the pan hard rod bushings which were about 6 years old, I could see visible deterioration—I used a large screwdriver to pry them around a bit and check for slop which was obvious. A better way to check these bushings as well as the tie rod ends is to have another person move the steering wheel from side to side in small motions while inspecting each of the tie rod ends and bushings—everything needs to be firm. I took the pan hard rod off the truck and inspected the bolts and the hangers to make sure that there was no wear in these components. Often times, with a loose system, you can even ovalize the hanger holes which you should correct and the bolts can get very worn where the hit the hangers. Bolts and holes where good. Pressing out the bushings is easy if you have a hydraulic press (which I do) and if you don’t then stop off at a garage. I used sockets of the right size to press in and out the bushings. I put the pan hard rod back on the truck and test drove. I thought I was in the clear until I hit some rough pavement at 60mph and I still had the symptoms—not as bad, but totally still there. Crap. On to the Swivel Pin preload.

To check this, start with the drivers side wheel (on NAS) as the drivers side only has the tie rod attached to the wheel (the passenger side has the drag link and the tie rod) connected to it. Remove the wheel, disconnect the tie rod and see how loose the hub is from side to side. If it feels free to move without resistance, then it is too loose and you will need to adjust your preload. I could detail how to do this, but this article does a great job: http://www.lrforum.com/articles/00034/index.htm You might need additional shims (they come in .003”, .005”, .010” and .030”) or you might not—there is a “stack” of shims at each upper bearing (mine had a .005, .010 and .030, I had to take leave in just the .030 and kept the other two for future). The entire preload adjustment took about 2 hours including refilling the swivel balls with grease. You will loose grease when you do your swivel pin preload, so make sure you have some on hand. There are procedures for minimal grease leakage using a jack stand under the hub and a floor jack under the axle, but I still leaked some and felt it would be a good idea to change out the grease anyways.

So, when encountering DW’s, make sure your linkages are all tight, your tires are balanced, your bushings are good and your swivel pin preload is adjusted—you should be good to go.

End result of all this—no more DW’s.

Hope this may help others.
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  #2  
Old October 31st, 2011, 12:06 PM
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Good post, I hate seeing all the people out there mistakenly blame the steering damper.
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Old October 31st, 2011, 12:12 PM
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Great post. Printed and filed. Take no offence, but this is one post that I hope to never have to pull out.
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  #4  
Old October 31st, 2011, 03:49 PM
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Also, one area that many people might not know about is the gearbox. Much of the DW problems do start from there as well as among other areas mentioned above. Since wear occurs in all areas of the steering system you must reduce any free play or enjoy the near death experience that fallows haha.
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Old November 1st, 2011, 11:08 AM
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Chris Davis
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I can see how slop in the steering system can cause DW's--which is definitely the focus above---how does slop in the gearbox equate to DW's? I suppose that a slack drivetrain may initiate DW's in an already out of tune steering system but I am failing to understand how a gearbox could actually cause DW's. Especially under load, most of drive train issues do not cause occillations. Could you please explain that further so that we know what to look for please?
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Old November 1st, 2011, 12:03 PM
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I have a harmonic wobble/vibration a little over 60mph. As I increase to 70, it diminishes but is still present and still harmonic. It shows itself in the steering wheel. I have replaced all 3 of the tie rod ends and the pitman arm joint. I have tighted-up the steering box wear screw and I've checked the swivel pins for play and took a little slack out of the wheel bearings pre-load. The only thing I can think of is an imbalanced front tire, but my experience with an imbalance is that at some speed, and higher, the shaking gets progressively worse and remains continuous NOT harmonic (comes & goes at predictable intervals). But that is not the case with my wobble/vibration, mine gets somewhat better. Any thoughts? Mine has 135K+ miles on it.
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Old November 1st, 2011, 12:08 PM
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Dennis, have you checked the u joints and slip joints on both drive shafts. I had a horrible harmonic that disappeared when I fixed a bad slip joint.
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Old November 1st, 2011, 12:32 PM
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Baird M. Gehring
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Dennis,
The steering box wear screw you mentioned, is that the screw/nut on top of the steering box? I recently had my D90 aligned, replaced panhard bushings, pitman rebuilt, tie rod ends, etc. and I still get a little play in my wheel between steering right and left. The shop who did my alignment didn't want to touch the steering box screw but would adjusting that probably get rid of some of the play in my steering? and how are you supposed to go about adjusting it?
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Old November 1st, 2011, 01:04 PM
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Quote:
Originally Posted by BMGmotors View Post
Dennis,
The steering box wear screw you mentioned, is that the screw/nut on top of the steering box? I recently had my D90 aligned, replaced panhard bushings, pitman rebuilt, tie rod ends, etc. and I still get a little play in my wheel between steering right and left. The shop who did my alignment didn't want to touch the steering box screw but would adjusting that probably get rid of some of the play in my steering? and how are you supposed to go about adjusting it?
Yes, on top. It's a tough one to get to. I tightened mine up (loosen nut, turned allen screw 3/4 turn clock-wise). I had the front of the D off, changing the timing belt, and access was good from here. Short of pulling the alternator on a 300tdi, getting to the nut & allen would be tough (my allen was plugged with silicon, so I had to clean that crap out 1st). OK, now for the book version. You need 2 people, one to turn the wheel and check for play and the other to operate the nut & allen wrench. With the engine running(I love moving parts & flesh...not!), turn the allen tighter (clockwise) until the "driver" senses no free play and observes the tire moving as the steering wheel moves. Tighten the locking nut. Done. But it's like you note, all the other points of play have to be removed 1st.

------ Follow up post added November 1st, 2011 10:08 AM ------

Quote:
Originally Posted by grnrvrs View Post
Dennis, have you checked the u joints and slip joints on both drive shafts. I had a horrible harmonic that disappeared when I fixed a bad slip joint.
Not the slip joints, but the U-joints were replaced this summer too. Changing the U-joints got rid of another low level, continuous vibration I was having. I do lube the "slips" every year. How do I check the slip joints? Wasn't aware that they were really something that could wear-out.
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Old November 1st, 2011, 02:47 PM
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Quote:
Originally Posted by Dennis View Post
Not the slip joints, but the U-joints were replaced this summer too. Changing the U-joints got rid of another low level, continuous vibration I was having. I do lube the "slips" every year. How do I check the slip joints? Wasn't aware that they were really something that could wear-out.
On mine, by pushing upward at the slip joint it deflected ~1/8". I'm confident that it did not get regular lube.
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Old November 1st, 2011, 02:52 PM
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@Dennis--harmonics are wierd and it could certainly be a tire imbalance as I had that with my BFG MT's. I also had a vibration harmonic similar to that with the tread of the old Big-O mud terrains at 60mph--it was a tire fault, not an imbalance fault, and they took those tires back (I swapped tires to show that there was no harmonics with the other tires...). You could even rotate the tires front to back to see if that changes anything. I have had a front driveshaft cause that sort of harmonic as well.

I just want to say that harmonics, espeically those that you can feel in the steering wheel, are not what I originally posted about--just to avoid any confusion. DW's are stupid scary, vibrations are annoying. Vibrations/oscillations can definitely be caused by the drivetrain or the steering system and are much trickier to track down. The first thing I do to help eliminate some areas are to individually remove the drive shafts and drive the truck to see if that can narrow things down. Then I rotate the tires and see if that narrows things down. Then it gets trickier.

For the steering box, with the truck turned off, grab the input shaft that connects the steering wheel to the steering box and rotate it back and forth--this is how you find out how much play you have. You tighten the screw to remove this play until it has no play and then I back it off 1/4 turn. Too much tension causes accelerated wear, so not too tight.
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Old November 1st, 2011, 06:51 PM
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Interesting post! In motorcycling we call this a tank slapper.. I Had to take a little helicopter ride many years back because of one and had no idea it occured in cars/trucks as well.. Scary stuff...
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Old November 1st, 2011, 07:23 PM
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Quote:
Originally Posted by Dennis View Post
I do lube the "slips" every year.
?? The service interval for u-joints is every 5,000 miles. Why would you lube the u-joints and not the slip joint. Seems like false economy to me.
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Old November 1st, 2011, 09:49 PM
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Originally Posted by Antichrist View Post
?? The service interval for u-joints is every 5,000 miles. Why would you lube the u-joints and not the slip joint. Seems like false economy to me.
I do lube both while I'm under there, I just didn't mention it. Now, McGyver status restored!
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Old November 2nd, 2011, 01:03 AM
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Quote:
Originally Posted by Davis View Post
I can see how slop in the steering system can cause DW's--which is definitely the focus above---how does slop in the gearbox equate to DW's? I suppose that a slack drivetrain may initiate DW's in an already out of tune steering system but I am failing to understand how a gearbox could actually cause DW's. Especially under load, most of drive train issues do not cause occillations. Could you please explain that further so that we know what to look for please?

You kind of answered the question with freeplay slack in the steering system can causes DW. The pitman arm and steering box are the starting points of the system. If you have a good amount of free play there you will start the chain reaction. You can replace all the parts in the system and still get DW if the box is very lose. It will still oscillate given the right road condition and speed. Just because a box has some free play doesn't not mean you will get DW but over time you will have more free play with wear and also have worn other steering parts which has a compounding effect. How do I know it can cause DW? I found out on my Jeep Grand Cherokee. I did it all! Arms/joins/ 3 Steering Dampeners oh the humanity. I had 250k miles on the orignal box. I though no way that would cause it but it had so much free play how could it not? After that no more DW. I knew the Defender had a way to adjust the box and was going to post or research this but you guys have posted about it thankfully. I really recommend everyone to do the adjustment first then see how it feels after. Your going to be surprised at how much better it will feel over those bumps so long as the other parts are not blown.
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Old November 2nd, 2011, 06:42 AM
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I can see how slop in the steering system can cause DW's--which is definitely the focus above---how does slop in the gearbox equate to DW's?
I read it the same way at first, then realized he was probably talking about the steering gearbox, not the transmission.
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Old November 2nd, 2011, 11:44 AM
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@Defenderpilot--you are absolutely right and yes, Tom, I thought he meant the transmission gearbox. You definitely have to check the gearbox as well--I should have had that as a bullet point at the top and missed it completely so thanks for bringing it up, George. I covered the tightening of this in post 11 on this thread and it definitely should be one of the quick-and-easy things that we all should check.

As even another point that I missed (but directly related) is I have had the Pitman arm (the arm coming off the steering box connecting the box to the drag link) come loose a couple times after it was replaced. Typically this arm is frozen onto the shaft and I (and a lot of others) have cursed this arm in the past for not coming off when we have to replace the ball joint. But when putting on the arm, you really need to take a hammer and "seat" it all the way up on the splines as tightening the bolt alone sometimes doesn't do the trick. A loose arm is easy to tell when someone is turning the wheel and you are under the truck checking your tie rod ends and bushings--just remember to check the pitman arm too.
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Old November 3rd, 2011, 01:25 AM
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Can't wait to adjust the box and seems easy since the screw is up top? One thing though off topic is that I have a leak from that adjustment screw? Would the washer nut alone fix it or something else maybe? Seems like it's a common area for them to leak so though I asked?
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Old November 4th, 2011, 07:56 PM
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Trying to get the allen nut lose from the lock nut, is it possible to completely unscrew the allen screw & locknut from the steering box all together or will that mess something up? I believe the allen screw is frozen to the locknut, perhaps some rust b/w the threads, so if possible I would like to unscrew both and try to losen the allen screw from the locknut on a bench. The locknut was stuck pretty tightly as well.
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Old November 5th, 2011, 08:07 PM
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Smile

Nevermind, some WD-40 did the trick. Thanks Dennis for the instructions on how to adjust that screw, no more play in my steering now.
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