Inducted into the Death Wobble club tonight (long post, sorry...)

[Greg Boardman-RIP]

I don't think lift has anything to do with it. Yes I do have the T. Rex system but I am running stock ride hight springs in the front. I was wanting to keep stock suspension geometry to try to cure DW. The only thing left was the tire and load rating. I have replaced steering box, shocks, springs, track bar, steering stabilizer, tires and wheels, and the only cure was to go to a load range "E" tire.





Greg

 

[Yo Hoot]

I don't think lift has anything to do with it. Yes I do have the T. Rex system but I am running stock ride hight springs in the front. I was wanting to keep stock suspension geometry to try to cure DW. The only thing left was the tire and load rating. I have replaced steering box, shocks, springs, track bar, steering stabilizer, tires and wheels, and the only cure was to go to a load range "E" tire.





Greg

Did you go with a stock replacement track bar?

 

[Greg Boardman-RIP]

Did you go with a stock replacement track bar?

Yes sir... ... ... ... ... ... ... ... ... ... ... .

 

[DPelletier]

So Greg,

What was your caster set at when you had the DW? Replacing your tires "cured" your Death Wobble, but again, I believe that you simply closed the path of least resistance. A properly engineered and set-up steering and suspension system shouldn't be so finicky as to require you to use a particular brand of tire (or sidewall stiffness or air pressure, etc. ). It's only my opinion, but your results are still consistent with my hypothesis. Caster shimmy can be induced from both too little (more common) or too much positive caster adjustment. Your case may be one of the exceptions, but I still think you'll find that the vast majority of DW trucks have had changes to thier front end geometry (statistically speaking).





Dave

 

[jimk]

I have experince that one time an I did not believe that the truck could shake like that. I had a trailer on it and I was going on a rippled road and it was like a resonant vibration. I slowed down an stopped the vibration. I am going to replace the track bar just to be sure that did not cause it. I have to wonder if the flexing of the side walls has a effect on the vibration. Stiffer side wall may provide damping to help the vibration. As a side note I dont like to buy tires that require a lot of weight to balance. I ask up front to be sure that I buy a tire that is close to begin with. Jimk

 

[Greg Boardman-RIP]

DP.

Truck has been aliened at the dealer and a private mech.

 

[DPelletier]

Greg,



Yeah, but to what settings. Rumor is that the factory recommendations are too wide a range to adequately deal with the problem. I think 4 deg. positive was optimum.



Cheers,



Dave

 

[Greg Boardman-RIP]

Thanks,

I will check it in the am. 4* right?

 

[DPelletier]

Greg,

I'm just going off memory with the 4deg. Do a search. There was a member who is an alignment guy that had the whole thing spelled out nicely in his post. Sorry, I can't remember the guy's name.



Dave

 

[Greg Boardman-RIP]

Dave,

I tried you 4degree setting and it seemed to work fine. Then all of a sudden I was off of the hwy and... ... Just kidding. I'll do a search and check it out tomorrow.



Greg

 

[TexBamBam]

I am not sure it is only in lifted trucks... . the guys at 4wp think its in the factory design with the rubber on rubber trackbar is the real cause. I have no clue except it sure scares the He** out of a person when it happens going 80... . and ruins a good pair of shorts in the process. I think I will try the 37" MTR's next... . what size lift do I need for those?

 

[hasselbach]

This is a very common problem with lifted Jeep Wranglers. When you change the height in the front end you change the axle camber. You need to find a good alignment shop and have them rotate the axle back within factory spec.

Camber is fixed and will not change, the caster is what is changing. Camber is the inclination inward of the wheel, whereas caster is the change in the axis of the ball joints.

 

[TexBamBam]

What ever it is... camber--caster sure scares the holy h*** out of a person when it happens.

 

[hasselbach]

has anyone noticed that when you lift the front end, even 2 inched, that the entire front axle moves laterally due to the drag link design? If I raise mine 2 inches, I am thinking of welding up a bracket on the frame to relocate the drag link lower to compensate for this. A longer drag link will not solve the angle change of this critical link, but dropping the pivot point to keep the factory specs will.

 

[Yo Hoot]

True but after lifting mine the 2" there isn't much of an angle change. Not sure if it's worth it but if you do it it will be the correct way to fix that change in geometry.



Distance between attach point centers is 39". If you do the trig, assuming the bar is lets say 5 degree angle in stock position. . the difference is in the 3/8" or less range. in axle location under the truck

 

[hasselbach]

True but after lifting mine the 2" there isn't much of an angle change. Not sure if it's worth it but if you do it it will be the correct way to fix that change in geometry.



Distance between attach point centers is 39". If you do the trig, assuming the bar is lets say 5 degree angle in stock position. . the difference is in the 3/8" or less range. in axle location under the truck

I politely disagree. When you figure that front ends are measured in extremely small increments (percentages of degrees), 3/8 of an inch is a mountain!



If you raise the front end 2 inches, I firmly believe you will need to drop the pivot point 2 inches. Remember, the more the track bar becomes vertical, the acceleration of change also occurs (meaning that the movement laterally of the track bar shall increase per each incremental movement of the axle downward. Say the axle moves 1/8 of an inch for the first 1 inch of downward drop, but from inch 4 to 5 drop, the axle will move not 1/8 but more like 1/4, due to the arc of the track are. ) I've seen this occur on our 4 links in our race cars, and an improperly track bar can yield horrible handling. The best angle for the track bar would be almost horizontal at rest, whereas upward and downward movement would occur past the zero point of reference. Actually better would be two track bars with a pivot on the axle in the middle point, but not sure if room would allow it. No matter how much lift you add, the dual track bar will hold a zero lateral position.

 

[Yo Hoot]

I politely disagree. When you figure that front ends are measured in extremely small increments (percentages of degrees), 3/8 of an inch is a mountain!



If you raise the front end 2 inches, I firmly believe you will need to drop the pivot point 2 inches. Remember, the more the track bar becomes vertical, the acceleration of change also occurs (meaning that the movement laterally of the track bar shall increase per each incremental movement of the axle downward. Say the axle moves 1/8 of an inch for the first 1 inch of downward drop, but from inch 4 to 5 drop, the axle will move not 1/8 but more like 1/4, due to the arc of the track are. ) I've seen this occur on our 4 links in our race cars, and an improperly track bar can yield horrible handling. The best angle for the track bar would be almost horizontal at rest, whereas upward and downward movement would occur past the zero point of reference. Actually better would be two track bars with a pivot on the axle in the middle point, but note sure if room would allow it. No matter how much lift you add, the dual track bar will hold a zero lateral position.

Thanks for the experienced take on this subject, hasselbach



I just wished the aftermarket would address this stuff more completely so we didn't have to waste our time and worries and just buy the parts we need.



Right now there is noting available for the track bar or bracket. Truck has been out for two years now. I have an appointment on 30th of next week to get a linked track bar made up. Maybe I'll see If I can work in some kind of drop bracket also. It looks like plenty of room there to fab and install something.

 

[DIESELMAN]

When you raise the front end, yes the track bar moves the axle over. It is supposed too. Think in three dimensions for a minute here. There are two FIXED links in the lateral plane, one is the stearing drag link, connected to the pitman, and one is the drag link.



The purpose of the drag link is so that when the axle moves up for instance, the pitman arm, which is fixed by your white knuckle grip, doesn't move. If the axle only moved straight up, unconstrained by the track bar, then something has to give. The drag link being compressed pushes the right wheel, and of course pulls the left wheel, causing bump steer to the right, and the opposite when the axle returns.



The Track Bar is a parallel link to the drag link so tha the axle moves, relative to the frame, in an arc, such that the axle on a bump moves right the same amount that the drag link is being compressed, and thereby eliminating the bump steer.



No matter how much you lift the truck you must not lower the frame mounting point of the track bar UNLESS you also drop the pitman arm as well. The Track Bar and Drag Link MUST ALWAYS BE PARALLEL. If it isn't then you will have bump steer. Hit a bump and it heads for the ditch, you pull the wheel left, the front end unloads, and it swerves way back to the left, you slam on the brakes and it pulls right etc.



A Loose track bar causes wandering, and will only cause DW if it is really, really Ducked up (sic).



There are two kinds of DW, one is alignment related, the other is a spring rate problem. And all are kept in check by tight front ends, tight shocks, high dampening rates, good steering dampner, good condition balanced tires with equal air pressure and equally firm sidewalls, tight ball joints and steering, track bar, link bars all tight, no frame cracks, perfect rear end thrust alignment, caster within range and correctly staggered for the un-adjustable camber.



Any one of these gets outa wack, and the conditions for a wobble begin to appear, get enough out of whack, and you get DW.



When all are perfect, each fault has its own characteristic, but if many things are wrong then its hard to determine what is wrong, and the process of elimination only works up until you fix the straw that breaks the camels back, but there is usually more wrong than what gets fixed, you just fix the one that in combination with the others allowed the genie out of the bottle.



The problem is all of these wear over time, but we drive the truck every day and the changes are gradual, until enough things are worn and we get a 30 second workout on the overpass.

 

[hasselbach]

I never thought of the drag link, track bar relationship, but it makes sense. The front end would have been better off with leaf springs and a more typical tie rod set up. My neighbor raised his truck 2 inches, and actually lengthen the track bar to compensate for the 3/4 inch movement in the front end when the lift was installed (obviously realigning the front). He used 1. 25 inch pipe and welded it up after cutting it.

 

[Yo Hoot]

I feel a link ended track bar will help. Out with the rubber. i think Dodge uses rubber to allow the three dimensional movement during suspension travel. Heim joints will eliminate compression/expansion but provide full articulation in those joints. I'm not so sure they used rubber as shock/vibration damping. I think it's cost. Most road jarring is handled by the coil springs and control arm bushings.