3g Death Wobble

[THUREN]

Hi all...



As you can imagine, I run into a lot of these death wobble situations, and to start off this post I want to be clear about a few things. Also keep in mind that these are all my personal OPINIONS, so take them for what they are worth... .



I firmly believe... .



~ The name and numbers on the side of the tire has nothing to do with death wobble. As noted somewhere above, that would mean that everyone with that type/size/brand would get death wobble, and it doesn't work that way. E rated tires may resist going into death wobble a bit better than D rated tires, but that isn't the root of the problem causing the DW. Just as a E rated tire may make it a bit harder to get the DW going(vs. D rated), a larger tire will exibit a higher chance of getting the DW going also. BFG gets a bad rap cause that's what tire shops have in stock, and everyone wants. Take a poll of ALL trucks(not just dodge) and see what brand "all terrain" is most popular. If changing out popular worn tires with many miles, to a different brand new ballanced tire, and the DW goes away, it's the fault of the "worn/out of ballance" tire and not the name on the side...



~ No truck is the same, so don't assume what the problem is. Example... . I just had a customer call me the other day and he had MASSIVE DW and had tried everything. He finally got to looking under the truck and the pitman nut was loose. Tightened it up and no DW... . It can be weird instances so look at EVERYTHING under your truck...



~ Dodges have one big flaw when lifted using the stock control arm locations... . When you lift/level the truck the control arms have now been angled more, causing the axle to move on a pronounced forward/up swinging arc. When you hit a straight-on bump with both tires at the same time it's not a big issue as the loads and geometry are ballanced left-to-right. When you hit a good sharp bump on one side the axle quickly swings forward, then snaps back, getting the DW occilation going. The reason is that the weight of the tire/wheel has momentum, so when you swing the axle forward/back, this momentum will be effective in swinging the tire around the ball joint radius, starting the DW. The heavier the tires/wheel the bigger this issue becomes. On this note the rim width/backspacing also plays a huge roll, as with a wider tire/wheel, the swing radius becomes longer. From a chassis design standpoint, the ball joints should be in the center of the rim anyway, but no solid axle trucks are like that.



If your DW starts on a smooth road at the EXACT same speed everytime, ballance your tires...



If your DW starts when you hit a sharp bump on one side of the truck, well, it could be anything LETTING the DW happen. This is why I'm starting to think the gearbox can play a huge roll on the dodges. Really, the truck should never get DW with no steering components in the truck at all, but with the forward swinging axle you need something solid(steering system) to prevent it.



Get the axle moving vertical, and most of these issues SHOULD go away... I've yet had a chance to really test my theory but it seems pretty simple to me. Look at it this way... . How many times do you hear that the DW started right when the leveling kit went on?



I post back when I have more time if there is interest...



-Don

 

[CJPerry]

Great post.

 

[HLewallen]

Hi all...



As you can imagine, I run into a lot of these death wobble situations . . .



keep in mind that these are all my personal OPINIONS, so take them for what they are worth... .



The name and numbers on the side of the tire has nothing to do with death wobble. . .



-Don

Wow. First of all, saying that these statements are your opinion is one thing, but you have presented yourself as an "expert", which carries with it a certain responsibility for what you say. So be prepared.



For you to say the type or construction of the tires have nothing to do with it is really just wrong. The tires are THE path of energy input to the system that is your suspension. They are a huge multi-dimensional spring and the physical link between the truck and the road. Those "letters and numbers" are your first indication of just what that spring rate is in all three dimensions, indicating differing construction details to fit different design goals. You are basically saying this part of the system has no effect on the dynamics of the rest of the system. Follow your own advice (at least this part) that DW can be attributed to any component of the system that will "let it happen". Beyond being a part of the system (just like balljoints, control arms, wheel bearings, etc. ), the tires are THE input to the system, and thus changing them changes the inputs ALL the rest of the system components see. In the case of DW the tires are definitely acting as torsional springs and probably have the lowest natural frequency of anything in the system.

 

[THUREN]

Heath...



If you had read my entire post, maybe you would have realized that I was implying that the brand name has nothing to do with DW, as that is all I meant...



I went into depth about the weight of the tire having a large part in the system so to be clear, sorry, I was only talking about the brand name and to a point, the rating of the tire... So again, the physical size and weight of the tire does have a HUGE effect on the suspension dynamics...



It would be nice to have an educated discussion, if anything before putting up a wall...



-Don

 

[THUREN]

Wow. First of all, saying that these statements are your opinion is one thing, but you have presented yourself as an "expert", which carries with it a certain responsibility for what you say. So be prepared.

N' yeah, I guess I would consider myself VERY experienced with Dodge front ends. EXPERT might be a bit of a stretch... .



But FWIW, the Dodge front end is basic compared to some of the suspensions I've designed, and I do love to talk-shop with people that tell me to "be prepared" especially...

 

[Task125]

Well said Don,

now let me ask you this,will your track bar help with or prevent DW ? Thanks Mike

 

[THUREN]

Well said Don,

now let me ask you this,will your track bar help with or prevent DW ? Thanks Mike

Mike,



Help with, FOR SURE, prevent definitely not... There are so many variables which contribute to DW, you can't put full blame in one spot.





I will say this. .



You could have the absolute PERFECT 5 link solid axle suspension design, and if the trackbar has slop you can still get DW, so a good trackbar is VITAL.



In my opinion, rubber bushings used for the trackbar on such a heavy truck is a downright bad design. Without a tight trackbar, you really can't go forward trying to eliminate DW, as even with everything else PERFECT, a trackbar that has any play can let DW happen. By design, rubber has play...



-Don

 

[Task125]

Thanks Don,

Are yours on sale or is that just free shipping? wanted to buy last month at the old price but my 2 and 4 year old had to eat. :-laf

 

[blmyachtsales]

Don I had a 96 4X4 dually out in MA. that had a bad death wobble and you were the only one that was able to speak sensibly about it and help diagnose the problem albeit a long tedious process. So again thanks on that one and you track bar is still holding up like new (50K on it). I now have an 06 QC 2500 4x4 and with 14K on it the steering started returning to center slower and slower till it finally stopped all together (this is where the death wobble signs started on the 96). First thing I looked at was the eccentric washer to see if the caster moved, sure enough the driver side has moved so it is giving that side of the axle allot les caster. the passenger side is still where I remember it being at 37miles. Have you heard of a new eccentric moving on it's own? truck has only on road milage and no actual death wobble, I ended up tach welding the 96 eccentrics in place, maybe I should do that to the new truck. Box feels nice and tight, everything is stock.

 

[NVR FNSH]

Mike,



Help with, FOR SURE, prevent definitely not... There are so many variables which contribute to DW, you can't put full blame in one spot.





I will say this. .



You could have the absolute PERFECT 5 link solid axle suspension design, and if the trackbar has slop you can still get DW, so a good trackbar is VITAL.



In my opinion, rubber bushings used for the trackbar on such a heavy truck is a downright bad design. Without a tight trackbar, you really can't go forward trying to eliminate DW, as even with everything else PERFECT, a trackbar that has any play can let DW happen. By design, rubber has play...



-Don

Then my '85 Toyota 4wd & '79 CJ-7 shouldn't ever experience DW..... Leaf springs and no track bar.



Don - just out of curiousity what suspension engineering - as in theoretical & analytical design - experience do you have?



Brian

 

[THUREN]

Then my '85 Toyota 4wd & '79 CJ-7 shouldn't ever experience DW..... Leaf springs and no track bar.

I sense the sarcasm, but yeah, ball joints can surely be one factor in your Yota/CJ getting DW. Actually, taking a blown out trackbar off the frontend of a leaf sprung vehicle(Superduty/YJ) can tame the DW... So there...



Leafs(with no trackbar) have enough side-to-side deflection that the axle won't hit a sudden stop, which sends a shock to the steering, making it abruptly change direction and get DW going...



Also, most leaf springs make the axle travel in a more vertical path(but still on an arc) so you don't have the balljoint swing issue...

Don - just out of curiousity what suspension engineering - as in theoretical & analytical design - experience do you have?



Brian

Brian, my background started with a strong mathematical influence(geometry,trig,calc), and then gravitated to suspension design(race cars in the beginning), in which I took a few basic classes in my late teens. Most of the learning done in those classes was almost usless so not much to brag about there. What I consider my real learning has been done in thousands of hours of my own reading, learning, building, and using my stupidly analytical brain to find the good and bad in designs. I have built a few mini models to check designs, built a few designs of my own, and have done quite a bit of suspension design consulting. For the most part, theory is used a bit for the strength aspect, but really, I go for overkill in that area. Every load can not be calculated, as it's hard to design for the truck crashing down on a suspension link. Beyond that, by doing almost EVERYTHING myself, I have learned A LOT in my 15 years or so of designing from the ground up. Only a few of these years have been "professional", but oh well...



-Don



FWIW, the Dodge 5 link front end is pretty basic compared to this 5 link I built/designed... This thing is driven every day in downtown LA. No death wobble, no funky handling, no swaybar, 90mph down the freeway fine, 16" of travel... ... No problems...

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[THUREN]

Don I had a 96 4X4 dually out in MA. that had a bad death wobble and you were the only one that was able to speak sensibly about it and help diagnose the problem albeit a long tedious process. So again thanks on that one and you track bar is still holding up like new (50K on it). I now have an 06 QC 2500 4x4 and with 14K on it the steering started returning to center slower and slower till it finally stopped all together (this is where the death wobble signs started on the 96). First thing I looked at was the eccentric washer to see if the caster moved, sure enough the driver side has moved so it is giving that side of the axle allot les caster. the passenger side is still where I remember it being at 37miles. Have you heard of a new eccentric moving on it's own? truck has only on road milage and no actual death wobble, I ended up tach welding the 96 eccentrics in place, maybe I should do that to the new truck. Box feels nice and tight, everything is stock.

Hi Adam!



I DO remember your situation...



On your 06',

I have noticed on a few of these trucks that the axle is not center in the body/frame, even stock. Same as if you had a leveling kit and didn't lengthen the trackbar. Since the lower control arms angle inward at the rear, it causes the axle to push forward on the passenger side and pull back on the driverside , when you don't adjust the caster cams to compensate. If your axle is not perfectly center in the body/frame(possible even stock), it would be normal to have the cams adjusted un-even or the truck will pull from the uneven wheelbase. .



I could imagine it would be possible to have one cam loosen, and the normal result would be less caster as the braking forces are HUGE. Keep in mind that caster is one of those adjustments that can be adjusted by YOU, and can be left alone(not needing an alignment) if the truck handles to your liking. It sounds like the axle is pushing back(less caster) if the steering is not returning to center as well. If your axle is centered perfectly in the body, the cams "should" be even on both sides, as long as everything is straight.



Another thing... Caster will not shift from side-to-side on these trucks(unless you add adjustable balljoints). When you hear people saying that they added more caster on one side(via the cams not adjustable balljoints) what they are really doing is altering the wheelbase. to correct a pull. What's probably happening is the wheelbase is being put where it should be. . :-laf



-Don

 

[TFauth]

As a new Dodge owner, I find these types of topics very informative. Alot of times you just have to sift through all of stories and figure out fact from fiction. It seems that don knows his stuff!! Oh yea, DW con also happen on a '04 ford 3/4 ton excursion. Just thought I would throw that in there.

 

[blmyachtsales]

Thanks again for the input Don. Just to see what would happen I marked the cams where they were (drivers side pointing toward the back of the truck just past the first rear notch on the axle and passenger to the front just forward of the first forward notch on the axle) then moved the driver side to match the passenger side. Drove it on the highway and the darn thing still wants to go left or right, never straight. Steering didn't feel different at all. The Tires are wearing funny on the outer edges as well, looking at the top of the tire the lugs are worn more at the front than the rear. I'm lost, this brand new trucks now has the same bad habits and symptoms my 96 did. By the way it this all happened over a 24 hr period, never hit a large bump or felt anything strange. I'm thinking about bringing it back to the dealer to let them worry about it but in I'm afraid they will make it worse.

 

[JessePayne]

question for Thuren

so by getting the axle to move more vertically opposed to forward on a bump do you mean returning the truck to stock height to correct the arc the axle swings when hitting a bump. what does the term backspacing mean when referring to tires/axle.

 

[DrDiesel]

I have never had any of my trucks get the death wobble as everyone calls it.

I have had the opportunity to see 2 fords have the front end shimmy while on the free way. The front tires looked like rubber bands.

Someone here has stated 40 PSI for tire pressure.

I run 65 front and 50 rear empty. If your tire pressure is low and you have not updated the front susp. components per the TSB from Dodge, your playing with fire.

 

[HLewallen]

Heath...



If you had read my entire post, maybe you would have realized that I was implying that the brand name has nothing to do with DW, as that is all I meant...



I went into depth about the weight of the tire having a large part in the system so to be clear, sorry, I was only talking about the brand name and to a point, the rating of the tire... So again, the physical size and weight of the tire does have a HUGE effect on the suspension dynamics...



It would be nice to have an educated discussion, if anything before putting up a wall...



-Don

Wow again. I apologize for not checking back on this topic. If you had read my post (and understood it) you would know I did not even mention the physical dimesions of the tire or the weight of the tire as specific inputs to the system. I was speaking specifically to the differences in stiffness between different tires (something that changes with tire manufacturer and specification - all those letters and numbers on the side of the tire). You have, I am sure, a great deal of practical experience with suspension repair and basic suspension design, and I am very happy your Dakota suspension works. But can you tell me at what frequency any mode present in that system resonates? If Calculus is the peak of your math credentials, I am pretty sure you can't. And I am smart enough to know I can't either - I would need an expert to perform an FEM analysis, and probably validate that model with accelerometers all over the suspension of several trucks with DW.



Your ego is writing checks other people's insurance can't cash (sorry - that statement is kinda being an *****, but Top Gun was on over the weekend . . . ) - please understand that some of your statements are moving outside of your practical experience. By sticking to what you know (you seem to know a good deal about finding areas in the suspension with play that can contribute to DW, and also designing specific components with less tendency to develop play) you can be established as an expert in that area. Stating absolutes in areas outside your expertise will weaken your credibility in all areas, even the ones you are an expert in! By the way - one of those "experts" from mechanical analysis has repeatedly told me that the dynamics of tire design are by far the most complex system he has ever worked with.

 

[DavidThompson]

QUESTION?... ... . IS THIS DW ONLY ON 4X4... OR... . 2X4..... AND WHAT YEARS... ... I HAVE A 07 2X4 DRW 3500 WITH RACK AND PINION STEERING... HAVING TO GET USE TO THE R&P STEERING... ... EVEN STOCK IT PULLS LIKE A GROWN MAN... ... trucksalesdave... . central Georgia

 

[JessePayne]

who said you got to be an expert on anything to post on this site. I would like to hear the guys opinion. Set your ego aside you may learn something

 

[THUREN]

Your ego is writing checks other people's insurance can't cash (sorry - that statement is kinda being an *****, but Top Gun was on over the weekend . . . ) - please understand that some of your statements are moving outside of your practical experience. By sticking to what you know (you seem to know a good deal about finding areas in the suspension with play that can contribute to DW, and also designing specific components with less tendency to develop play) you can be established as an expert in that area. Stating absolutes in areas outside your expertise will weaken your credibility in all areas, even the ones you are an expert in! By the way - one of those "experts" from mechanical analysis has repeatedly told me that the dynamics of tire design are by far the most complex system he has ever worked with.

Heath, I try hard to not come across as having ALL the answers. I DO have quite a bit of knowledge in this area though, and if you go back and read the very opening lines in my initial post, you will see that I specifically pointed out that EVERYTHING I say is MY opinion. You can NOT take everything you read on the net as facts and what I type is no exception...



I admire you for trying to weed out people who claim FACTS, as I hate that when truth is hard to come by, but that's not me so go preach somewhere else. I really do try and help and that is ALL I am trying to do.



I'll come back and answer the asked questions in the morning...