Violent Shake? Any help?

[mjeff87]

I get so sick and tired off being outbuilt and outwheeled by people that never that never built or wheeled anything except a computer chair !!!!!!!!!

 

:roll:

[HOrnbrod]

I get so sick and tired off being outbuilt and outwheeled by people that never that never built or wheeled anything except a computer chair !!!!!!!!!

 

:roll:

 

I think he's passed out now................ :nuts:

[chicofuentes0224]

I get so sick and tired off being outbuilt and outwheeled by people that never that never built or wheeled anything except a computer chair !!!!!!!!!

 

:roll:

 

I think he's passed out now................ :nuts:

 

That's funny. He had a couple posts over a couple threads that started getting, how you say in your country, not so nice. But I just read over his 26 posts and he seemed like a nice guy. Must be to much Bud Light Lime.

Damn you BLHTAZ :laughin:

[Eagle]

Eagle I can tell buy your response that you have never had the fun of death wobble , a vibration is one thing DW is a complete different thing . Pinion angle has nothing to do with DW . I would love to to have had it that I could just remove the front drive shaft a problem solved that is not how it works , I get so sick and tired off being outbuilt and outwheeled by people that never that never built or wheeled anything except a computer chair !!!!!!!!! To the young man that asked the question start at your lower control arm bushings and come up from there.

Since you misunderstood my post and you don't know jack about me, I don't know why I waste my time responding except to straighten out misconceptions for the benefit of those with an open mind.

 

Yes, I have experienced death wobble. I know exactly what it feels like and why it is called what is is.

 

I did not say that pinion angle has anything to do with death wobble. I said that caster angle has a lot to do with death wobble. But because the front axle is a welded assembly, when you change the caster angle you also change the pinion angle, and when you change the pinion angle you change the u-joint operating angle. Which means that, as one of the other gents correctly expressed it, when dealing with a lifted rig you are seeking a compromise that (hopefully) allows you to have enough caster to prevent death wobble while having a low enough u-joint angle to avoid excessive vibration and rapid destruction of the u-joints.

 

Now, if you'll excuse me, I'm going to drive my computer chair down to Rausch Creek and play ...

[Pete M]

I'm terribly sorry, but I just couldn't resist. :razz:

 

 

[CWLONGSHOT]

Eagle I can tell buy your response that you have never had the fun of death wobble , a vibration is one thing DW is a complete different thing . Pinion angle has nothing to do with DW . I would love to to have had it that I could just remove the front drive shaft a problem solved that is not how it works , I get so sick and tired off being outbuilt and outwheeled by people that never that never built or wheeled anything except a computer chair !!!!!!!!! To the young man that asked the question start at your lower control arm bushings and come up from there.

 

Ex,

Your new so I'll cut you some slack. Once you get a chance to look up and read all the great and extensive information we have here you will realize who's who and what's what. Hopefully you'll grow to garner the respect Eagle has achieved here. He has been here a while and helped out just about all of us at one time or another. He knows his stuff and is willing to help and share it. I know these people exist, lord knows I do my best to oust them and stop the miss information form flowing. but know this, Eagle is not an arm chair commando.

 

SO, grab a beer and start reading and you will quickly learn the pecking order here. We are nice group of guys. For the most part, we get along pretty good also know that some of us have teeth. But its no pirate, we don't want it that way!! In no time you will realize dining on your own foot isn't so great.

 

CW

[BLHTAZ]

On the serious side... Well said CW. It was what I was thinking...but just couldn't say the way you did.

 

 

On the lighter side... Not making light of it in any way, but I feel like a ... (Like Pete...I couldn't resist)

[exjay33]

Well then it seems to me the pecking order should not point someone in the wrong direction . If you check around you will find most people have this problem after lifting correct ? This is a caster problem not a pinion angle problem . Most of the time DW is related to the lower control arm bushing which after 100K are cracking breaking down if you are past 3" change them make them 3/4" longer most time problem solved then have it lined up , or next step track bar frame side mount loose or shot . Have you ever had severe death wobble or just the 55mph shimmy like alot of people have and think this is DW ? Once you have it you won't even want to drive your ride for fear of the result. And as far as the steering stabilizer its like taking a tylenol for a brain tumor !

[BLHTAZ]

On the solid D30 axle, caster & pinion angle are one-in-the-same. The only way to change caster without changing pinion angle is to take the knuckles off and rotate them seperate from the housing. You are saying the same thing that we are...just in a different way. Changing caster (pinion angle) also adversely effects toe and camber and none of this can be properly set by anyone other than someone with the proper knowledge and alignment equipment. ;)

 

I do completely agree with you on the steering damper thing though. It has nothing to do with DW...can't cause it...can't help it :cheers: .

[exjay33]

Well Brent then you understand what you are saying then is that by decreasing pinion angle (which is what you do when lifting frt axle ,pinion angle on frt side go down and increases slighty on cv joint side which has no affect on it ) Why get away from the question he posted have it lined up if still DW move to lower control arm bushing . As a parts employee at dealership you can tell him this is a common problem that 12.00 a piece can solve . He states he only went 1 3/4 in puck correct ? Chances are it is a bushing issue ,,,,,1.75 lift does not change caster that much at that lift. That is all that I am saying

[exjay33]

I suppose I better clarify pinion angle statement or someone will mis the point . As you lift pinion angle on frt driveshaft goes down on our type of application,,,,the angle at which the pinion sits increases ( but you can mount an axle upside down it has to do with the relationship pinion to driveshaft is pinion angle ) This is why your rear axle pinion angle must be corrected with shims in some case because it doesn't have a built in caster ( some tj s have the adjustment bolts in theirs lower control s )

[Pete M]

One quick story on tire balancing. Don't ever just assume that they did it right. My old minivan developed some gawdawful shakes at freeway speeds right after the tire place swapped the directionals left to right (as part of the rotational schedule). I rotated the tires front to back and tried again but the same shaking was there. Took it back to the same tire place to have them look into it. They rebalanced everything and now it rides smooth as glass. Apparently someone was having an off day the first time? :dunno:

[BLHTAZ]

Well Brent then you understand what you are saying then is that by decreasing pinion angle (which is what you do when lifting frt axle ,pinion angle on frt side go down and increases slighty on cv joint side which has no affect on it ) Why get away from the question he posted have it lined up if still DW move to lower control arm bushing . As a parts employee at dealership you can tell him this is a common problem that 12.00 a piece can solve . He states he only went 1 3/4 in puck correct ? Chances are it is a bushing issue ,,,,,1.75 lift does not change caster that much at that lift. That is all that I am saying

Gotcha...we are on the same page and I appologize if I did not communicate propoerly or if I misunderstood what you where saying :cheers: .

[Eagle]

Let me post this one more time, for the benefit of everyone who is willing to listen. Then I'll go fire up my desk chair and go take a ride around the front yard.

 

There is NO single, works-every-time cause or solution for death wobble. NONE! It's a complex interaction. When I started working on the XJ Bible, I spent several months (yes, months) exchanging drafts of the proposed chapter on death wobble with a guy named Alyn, whom I considered to be the most knowledgeable guy in NAXJA regarding suspension design and geometry. Like me, he had some time in on race car chassis work, but he actually understood things like "roll center" that were (and are) essentially just words to me.

 

It had always been my experience that the single most prevalent aspect contributing to death wobble had always been tire balance. Alyn reminded me that if only one tire is out of balance, you can sometimes drive down the highway for 50 miles and have no problem. Hit a bump, and you have a problem So it's more than tire balance.

 

Then there are those who say it's caster (or lack thereof). Again, though, you can find people running far less caster than specified and they never have death wobble.

 

Then there's the track bar crew. "DW is always cause by a worn-out track bar." Well, no, it isn't. Some years ago, in the middle of a cold winter (when we still had those), the track bar on the '88 XJ got so bad that I had almost a half turn of free play in the steering wheel before anything started to happen at the front wheels. But ... while steering was somewhat less than precise, I drove it that way for several months until things warmed up enough to crawl under and replace it, and there was never even a hint of death wobble.

 

"It's the bushings" says ExJay33. The first (and worst) episode of DW I ever encountered was in a brand new, box stock 1999 Grand Cherokee WJ. It was six months old, had at the time about 8000 miles on it, and since I was wheeling the XJ it (the WJ) was my daily driver and completely, absolutely stock. I was headed down a long, shallow downgrade on a state road in New Hampshire at 55 MPH, lightly touched the brakes to hold the speed at 55 ... and all hell broke loose. I had to stop the vehicle to end it. I sold that piece of tin back to DaimlerChrysler at around 14,000 miles, but it never again exhibited death wobble. No worn bushings. No worn track bar. No bad alignment. Tire balance was perfect -- it rode like it was on glass most of the time. What happened?

 

Alyn and I finally agreed that the problem is so complex because it relies on a harmonic. If one front wheel starts bouncing around, you have one front wheel bouncing around. Not good, but no big deal. But ... when the bouncing in one wheel hits a frequency that allows it to start the opposite wheel bouncing, and then they mutually feedback and reinforce each other in a constant escalation, THAT's when you get death wobble. And it can any of a number of factors that sets it off, or a combination of more than one.

 

Regarding the WJ, I discovered that Jeep had a known (but unpublicized) problem with DW in export WJs. They fixed it by replacing the springs with a different rate. Mine had the optional UpCountry suspension. I assume the early U.S. spec UpCountry was the same spec as the European export suspension, but I've never been able to confirm that, and it doesn't interest me enough now to pursue it. What set mine off was warped brake rotors. The light touch on the brakes, combined with warped rotors, sent the caliper bouncing back and forth. That started the wheel wobbling slightly, and the suspension was just right to transmit that to the opposite wheel. BOOM! I had death wobble once on the '88 MJ, right after I had swapped the tires. Put the first set back on, and had no more death wobble. The frequency of oscillation of that particular set of tires happened to match the natural frequency of the springs in the MJ, and that's all it took. Dirreent set of tires weighed different and reacted different to the same road, so ... no death wobble.

 

Alyn and I also sort of agreed that it's important to distinguish between things that "cause" death wobble, and things that may "allow" or "contribute to" death wobble but can't "cause" it. Obviously, since I drove around for several months with a badly worn track bar and had no DW, it cannot be said that a worn track bar "causes" DW. Ditto control arm bushings. Ditto the steering stabilizer. Each of those things may help dampen the transmission of wobble from one side to the other and thus replacing worn components may help prevent the onset of death wobble, but they aren't the "cause."

 

Personally, I still hold the opinion that most of the time wheel balance is the real cause. However, I know there are instances when tires are perfectly balanced on a smooth road but hitting a bump can set off death wobble, so it's not ALWAYS wheel balance. But sometimes, like with my '99 WJ, it's going to be essentially built into the front suspension and it may be that only changing something will alter the dynamic. Different shock valving might offset a certain spring rate that has the magic harmomic frequency, for example. Increasing the caster angle changes the way the tires ride on the road, which is why that has an effect.

 

It's not a simple problem. It's fine to offer suggestions as to what things to consider, but it's also important not to fall into the trap of claiming that YOUR one-size-fits-all solution is THE answer, because ... it isn't.

 

I still always suggest tire balance first, but I long ago stopped saying that was the first, last and only thing you need to consider.

[SuperWade2]

Then I'll go fire up my desk chair and go take a ride around the front yard.

 

:jump: :clapping:

[brigarpeon]

Let me post this one more time, for the benefit of everyone who is willing to listen. Then I'll go fire up my desk chair and go take a ride around the front yard.

 

There is NO single, works-every-time cause or solution for death wobble. NONE! It's a complex interaction. When I started working on the XJ Bible, I spent several months (yes, months) exchanging drafts of the proposed chapter on death wobble with a guy named Alyn, whom I considered to be the most knowledgeable guy in NAXJA regarding suspension design and geometry. Like me, he had some time in on race car chassis work, but he actually understood things like "roll center" that were (and are) essentially just words to me.

 

It had always been my experience that the single most prevalent aspect contributing to death wobble had always been tire balance. Alyn reminded me that if only one tire is out of balance, you can sometimes drive down the highway for 50 miles and have no problem. Hit a bump, and you have a problem So it's more than tire balance.

 

Then there are those who say it's caster (or lack thereof). Again, though, you can find people running far less caster than specified and they never have death wobble.

 

Then there's the track bar crew. "DW is always cause by a worn-out track bar." Well, no, it isn't. Some years ago, in the middle of a cold winter (when we still had those), the track bar on the '88 XJ got so bad that I had almost a half turn of free play in the steering wheel before anything started to happen at the front wheels. But ... while steering was somewhat less than precise, I drove it that way for several months until things warmed up enough to crawl under and replace it, and there was never even a hint of death wobble.

 

"It's the bushings" says ExJay33. The first (and worst) episode of DW I ever encountered was in a brand new, box stock 1999 Grand Cherokee WJ. It was six months old, had at the time about 8000 miles on it, and since I was wheeling the XJ it (the WJ) was my daily driver and completely, absolutely stock. I was headed down a long, shallow downgrade on a state road in New Hampshire at 55 MPH, lightly touched the brakes to hold the speed at 55 ... and all hell broke loose. I had to stop the vehicle to end it. I sold that piece of tin back to DaimlerChrysler at around 14,000 miles, but it never again exhibited death wobble. No worn bushings. No worn track bar. No bad alignment. Tire balance was perfect -- it rode like it was on glass most of the time. What happened?

 

Alyn and I finally agreed that the problem is so complex because it relies on a harmonic. If one front wheel starts bouncing around, you have one front wheel bouncing around. Not good, but no big deal. But ... when the bouncing in one wheel hits a frequency that allows it to start the opposite wheel bouncing, and then they mutually feedback and reinforce each other in a constant escalation, THAT's when you get death wobble. And it can any of a number of factors that sets it off, or a combination of more than one.

 

Regarding the WJ, I discovered that Jeep had a known (but unpublicized) problem with DW in export WJs. They fixed it by replacing the springs with a different rate. Mine had the optional UpCountry suspension. I assume the early U.S. spec UpCountry was the same spec as the European export suspension, but I've never been able to confirm that, and it doesn't interest me enough now to pursue it. What set mine off was warped brake rotors. The light touch on the brakes, combined with warped rotors, sent the caliper bouncing back and forth. That started the wheel wobbling slightly, and the suspension was just right to transmit that to the opposite wheel. BOOM! I had death wobble once on the '88 MJ, right after I had swapped the tires. Put the first set back on, and had no more death wobble. The frequency of oscillation of that particular set of tires happened to match the natural frequency of the springs in the MJ, and that's all it took. Dirreent set of tires weighed different and reacted different to the same road, so ... no death wobble.

 

Alyn and I also sort of agreed that it's important to distinguish between things that "cause" death wobble, and things that may "allow" or "contribute to" death wobble but can't "cause" it. Obviously, since I drove around for several months with a badly worn track bar and had no DW, it cannot be said that a worn track bar "causes" DW. Ditto control arm bushings. Ditto the steering stabilizer. Each of those things may help dampen the transmission of wobble from one side to the other and thus replacing worn components may help prevent the onset of death wobble, but they aren't the "cause."

 

Personally, I still hold the opinion that most of the time wheel balance is the real cause. However, I know there are instances when tires are perfectly balanced on a smooth road but hitting a bump can set off death wobble, so it's not ALWAYS wheel balance. But sometimes, like with my '99 WJ, it's going to be essentially built into the front suspension and it may be that only changing something will alter the dynamic. Different shock valving might offset a certain spring rate that has the magic harmomic frequency, for example. Increasing the caster angle changes the way the tires ride on the road, which is why that has an effect.

 

It's not a simple problem. It's fine to offer suggestions as to what things to consider, but it's also important not to fall into the trap of claiming that YOUR one-size-fits-all solution is THE answer, because ... it isn't.

 

I still always suggest tire balance first, but I long ago stopped saying that was the first, last and only thing you need to consider.

 

Eagle,

That is one of the best darn disortations that I have read. I understand ALL the causes of DW. It's merely a matter of deduction of the correct source. I couldn't have written it in a better fashion as you've covered the bases. You know your stuff. :smart:

[HOrnbrod]

X2. Eagle has a way of breaking things down in a way we all can understand and act on. Except when he's out in the lower 40 cruising around in his power chair.

[86FUBAR]

Eagle i couldnt agree more with u , i got a 05 rubicon unlimited new off the lot and have experienced DW from the begning but only when i hit the right bump at a certin speed . now after about 10k i warped the front rotors (because the brakes are less than adaquit as they always have been) and that had increased the DW but only when i hit thesweet spot in the road wile braking . I'm at 27k right now and still experienc the DW here and there but try and keep the tires balanced and rotated as often as i can but the rotors are still warped and will stay like that , for now .

o ya and yes i could have just worn out my welcome at the dealership having them fix and replace stuff but i believed that it was as Eagle said "built in to the suspension" so to speak and not much they could do but just piss me off.

[mvusse]

When I had DW, it was always caused by either hitting a bump in the road with my ps front tire, or making a very slight right hand turn, always at 55MPH or higher, never below 55MPH.

 

What was allowing my DW to happen was both a loose track bar at the frame bracket, and worn bushings in the lcas. Bad ds front u-joint may or may not have been a contributing factor.

 

Now with new U-joint, new (to me) track bar + bracket and new lca bushings, I have not had it happen anymore, except for the one time the castle nut on the track bar loosened 1/4 turn (somehow the cotter pin came out). But even with the track bar being tight, I had experienced it before I replaced the bushings.

 

So in my case a loose track bar could allow it to happen, and worn/old lca bushings could allow it to happen. From what I understand, these are the first two things to check, in that order, but I imagine tie rod ends, wheel/tire combination and possibly even springs/shocks can factor into it.

[exjay33]

Well then after that let me take the time to issue my deepest apology , I still don't understand way you would point someone to the pinion angle when you didn't mention it ? If you are over 100k most logical place to start is bushing . I know ford still buys trucks back too this day due to wobble they can not explain . There are many factors to take into consideration he asked for the best place to start basicaly , So instead of all these treads leading a guy in 9000 different directions how about he gets pointed in the best place to start and go from there . Eagle I really mean no harm at , I know the first time I had it , I had spent well over a grand till I solved it , I hate to see someone else do the same . The reason I came to my answer is from his other posts he is working on MJ so it has got to be at least 16 years old. BY the way my computer chair has 6 wheels no tracks.

[Eagle]

You are the only person I have ever encountered who thinks the control arm bushings is the place to start. Most people say "Track bar." I say "wheel balance." Other people say "caster angle."

 

Take your pick, but don't try to present your guess as the ultimate solution. It ain't. My '88 Cherokee has 275,000 miles on the original control arm bushings, the front end clunks turning into driveways, one of the front tires is definitely out of balance, and I don't have death wobble.

 

Next case ...

[mvusse]

I think what Eagle was getting at is that caster angle can either cause or allow DW to happen. The only way to change the caster angle is to rotate the axle, which in turn changes the pinion angle. My truck is at stock height, so with the correct caster, the pinion angle is correct.

 

When you lift a Comanche (or Cherokee), you would want to rotate the axle to correct the pinion angle, but at the same time you are adversely affecting caster. So you'd have to find a balance between a good enough pinion angle, and caster being "close enough" for DW to not occur.

 

I did not reread the entire thread, though, and my memory is not the best.

 

Edit: to add that my last post is based on my personal experiences with my truck, and states my personal opinion. I have only owned my truck since February, and other people participating in this thread have far more experience than I when it comes to the idiosyncrasies of the MJ and XJ (and others?) front suspension.

[chicofuentes0224]

Hey in the melee,

Did ya ever get this fixed bra?

[highlandjeeper]

My MJ is still stock height with 235/75r15s. I have also been fighting a severe death wobble problem. We put in upper and lower ball joints in the PS as they were shot. DS ball joints are good. I also changed the steering gear as it had some play as well. After replacing what we could find to be the only worn parts, DW occurs much more frequently and at lower speeds. :mad: We couldn't see any play in the control arms or the track bar. I will have to inspect these much closer as well as check alignment. I need all of this fixed before I put the lift and bigger tires on. I am still confused as to why it got worse with replacing worn parts.

 

I guess I should check all of the bolts from when the PO swapped in the front diff.

[CWLONGSHOT]

My MJ is still stock height with 235/75r15s. I have also been fighting a severe death wobble problem. We put in upper and lower ball joints in the PS as they were shot. DS ball joints are good. I also changed the steering gear as it had some play as well. After replacing what we could find to be the only worn parts, DW occurs much more frequently and at lower speeds. :mad: We couldn't see any play in the control arms or the track bar. I will have to inspect these much closer as well as check alignment. I need all of this fixed before I put the lift and bigger tires on. I am still confused as to why it got worse with replacing worn parts.

 

I guess I should check all of the bolts from when the PO swapped in the front diff.

 

As soon as I hear someone say the have experienced DW... I look for the words "LIFT " to follow. As soon as you see that and read that the DW didn't ever occur before the lift and nothing else has changed... I think CASTER/ALLIGNMENT!!!!! The "CAUSE" and the "CURE" CAN be to separate and distinct issues. That's the BIGGEST reason this whole DW thing is shrouded in such a cloud of misunderstanding.

 

As has been said over and over DW has many aspects that can contribute.

 

CW