good ol' death wobble
07-10-2009, 11:15 PM
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good ol' death wobble
hey guys about a month ago i installed a new track bar and i thought i fixed the problem and now it is back. Could the track bar have possibly failed on me already!?! (not to worry though, it's a lifetime warranty.)
Could someone give me a list of where I should start looking?
Alignment is a bit off, keeps pulling to the right.
(I tried to get it aligned, but it STILL kept pulling to the right.)
Possibly control arms???
Tie-rod bushings are good and tie-rod in general
pittman arm is good
anywhere else i should check??
my wheels I am a bit concerned, but I am not sure if that could be the MAJOR cause of the problem. I am unsure if they are balanced, but they do have the correct PSI when I checked it.
I'm able to drive around the city fine, but as soon as I hit the freeway (65+ mph), I start to feel it shake and once I go over freeway bridges, those bumps trigger the death wobble
The jeep runs amazing (249k miles and going!!!) and I don't think its right to not let the jeep run to its full potential!!
Could someone give me a list of where I should start looking?
Alignment is a bit off, keeps pulling to the right.
(I tried to get it aligned, but it STILL kept pulling to the right.)
Possibly control arms???
Tie-rod bushings are good and tie-rod in general
pittman arm is good
anywhere else i should check??
my wheels I am a bit concerned, but I am not sure if that could be the MAJOR cause of the problem. I am unsure if they are balanced, but they do have the correct PSI when I checked it.
I'm able to drive around the city fine, but as soon as I hit the freeway (65+ mph), I start to feel it shake and once I go over freeway bridges, those bumps trigger the death wobble
The jeep runs amazing (249k miles and going!!!) and I don't think its right to not let the jeep run to its full potential!!
Last edited by kurvy; 07-10-2009 at 11:19 PM.
07-10-2009, 11:20 PM
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yeah i've definitely looked around the web and spent about a full day looking up potential death wobble causes. It IS probably the worst problem you could have with a jeep
07-10-2009, 11:37 PM
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it could be the combination of your tires being unbalanced and your alignment. thats what was wrong with mine. i put the 3" lift on, needed an alignment after that but did not have the DW. so i waited until i put 31 x 10.5s on and as soon as i did the death wobble occured, same situation as you (reaching about 60 65 mph). i went to my local tire shop and had them do the alignment and balance/rotate tires and i have not had one problem since. i think this could be your cure since you have inspected most of the other culprates to no avail. good luck hope you get it sorted out
07-10-2009, 11:43 PM
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Death Wobble... The Engineering Explanation
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
gearida
I worked as an Alignment guru for several years. When asked to explain or help in remembering steering angle terms I found a simple way to remember: 1) toe in and toe out - simple right if not find something else to do in your spare time...
2) Caster, my analogy is like fishing and throwing the pole from over the shoulder. This is the angle in question called caster, so if your arm is in the strong muscle man position as if you are prior to casting the fishing pole your forearm is at positive caster (strong muscle=positive)
If you are at full throw of the fishing pole or weak muscle man pose then you forearm is at negitive caster.
3) Camber, now give me some here, again take your forearms and think of them as straight up in front of you. Lean them out (as if your dates legs where apart) that is a positive...camber.
If your forearms are again straight up in front of you and your fists are coming in close together (as if your dates legs are closing) this is negative...thus negative caster.
I hope you don't forget my little story!
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
09/20/06, 08:29 PM
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
gearida
09/10/07, 03:42 PM
2) Caster, my analogy is like fishing and throwing the pole from over the shoulder. This is the angle in question called caster, so if your arm is in the strong muscle man position as if you are prior to casting the fishing pole your forearm is at positive caster (strong muscle=positive)
If you are at full throw of the fishing pole or weak muscle man pose then you forearm is at negitive caster.
3) Camber, now give me some here, again take your forearms and think of them as straight up in front of you. Lean them out (as if your dates legs where apart) that is a positive...camber.
If your forearms are again straight up in front of you and your fists are coming in close together (as if your dates legs are closing) this is negative...thus negative caster.
I hope you don't forget my little story!
07-10-2009, 11:47 PM
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07-11-2009, 12:04 AM
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this thread should be a sticky...seems like everyone from time to time has to deal with the death wobble. thats why I joined this forum...i'd bet money that is the reason most people join this forum.
07-11-2009, 12:44 AM
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Death wobble is why I originally joined. But has been helpful in several cases now.
About every 25,000 miles or so I have to take mine in and have the tires balanced.... goes away every time until another 25,000.
About every 25,000 miles or so I have to take mine in and have the tires balanced.... goes away every time until another 25,000.
07-11-2009, 07:45 AM
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Start off by balancing your tires. They shouldn't be shaking at 65 mph. Next get someone to steer while you watch for movement in any of the tie rod ends and trackbar. Make sure the trackbar is TIGHT.
07-11-2009, 08:40 AM
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are you sure you had the death wobble? that's when your front tires start shaking left and right and you have to slow down just to get back in control. I can't see how a sway bar will cause the death wobble cuz the sway bar only controls the swaying, not tires wobbling.
07-12-2009, 01:49 AM
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thanks guys for the info and thanks mike for the huge post .. i've definetly read that and was looking to book mark that.
I really do think it is balancing + rotating tires, i'm definetly going to check that out tomorrow, but also, my tie-rod ends are shot as well, which could possibly be a contribute to the death wobble
--added note on the rotation
my jeep also pulls to the right EVEN after I took to an alignment shop, I looked at the treads and there is alot more wear on the front right than my front left .... deff going to rotate tomorrow + see if I can get them balanced ..
I was also wondering if I DO rotate my tires, do I NEED TO GET THEM ALL BALANCED???? Or just be good with the two that are coming to the front????
I really do think it is balancing + rotating tires, i'm definetly going to check that out tomorrow, but also, my tie-rod ends are shot as well, which could possibly be a contribute to the death wobble
--added note on the rotation
my jeep also pulls to the right EVEN after I took to an alignment shop, I looked at the treads and there is alot more wear on the front right than my front left .... deff going to rotate tomorrow + see if I can get them balanced ..
I was also wondering if I DO rotate my tires, do I NEED TO GET THEM ALL BALANCED???? Or just be good with the two that are coming to the front????
Last edited by kurvy; 07-12-2009 at 01:56 AM.
07-12-2009, 01:50 AM
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x2 on that, that is the original reason why I joined this forum.
I have done alot of research though with google.com
It is great to see that I am not alone with this problem!