JT4x4
The Mud Pit => Wrenching => Topic started by: GreenGrandV8 on May 14, 2010, 04:32:05 PM
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every time i drive on the road, if i get over like 40 i get really bad death wobble and i want to fix it. i was wondering were the 1st best place to start would be?? should i just get a good steering stabilizer?? kevinsoffroad has a good one for 59$$ anyone with helpful hints let me know please. i want to be able to drive my jeep normal and not hold up traffic lol
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Steering stabilizers only mask the DW, they do nothing to actually fix the problem. Here is the best writeup I've seen yet on DW and how to fix it. It was on a Cherokee forum, but we all share the same front suspensions. I suggest printing and reading through it a couple times.
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 balls 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
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
Curing deathwobble is definetly a reality. Deathwobble isn’t similar to a wobble from an unbalanced tire. It is by far worse. When deathwobble hits you will know… it’s a violent shake form the front end that feels like the Jeep is about to fall apart. Usually when it happens the only thing you can do to stop it is slow down. The first steps to eliminate deathwobble should be a visual inspection of each component, check the bushings, tire balance and an alignment. There are some common things you must check anytime you lift your Jeep. Deathwobble is experienced mostly on lifter Jeeps, however it is not uncommon for someone without a lift to experience the dreaded DW. Listed below are a few things you can check.
Torque specs:
Item ........................................ Ft. lbs. ................... Nm
Lug nuts (1/2 X 20 w/ 60* cone) .... 85-115 .............. 115-150
All tie rod ends ............................ 55 ..................... 74
Steering (both ends) .................... 55 ..................... 74
Shock absorber upper nut .............. 16 ..................... 22
Shock absorber lower nuts ............. 17 ..................... 23
UCA frame end ............................. 66 ..................... 89
UCA axle end ............................... 55 ...................... 74
LCA frame end ............................. 85 ...................... 115
LCA axle end ............................... 85 ...................... 115
Track bar frame end ..................... 60 ...................... 81
Track bar axle end ....................... 40 ....................... 54
Track bar bracket bolts ................. 92 ....................... 125
Track bar bracket nut ................... 74 ....................... 100
Track bar bracket support bolts ...... 31 ....................... 42
Hub bolts (3) ............................... 75 ....................... 102
Hub- axle bolt .............................. 175 ..................... 237
Alingment specs (stock):
Angle ............. Preferred ........... Range ............. Max R/L diff.
Caster ............ +7.0* ........ +5.25* to +8.5* ......... 1.25*
Camber ........... -0.25* ....... -0.75* to +0.5 ........... 1.0*
Total Toe-in .... +0.25* ....... 0* to +0.45* ............. .05*
Thrust angle .... 0* to ± 0.15*
Check your Track Bar, play in this can cause the axle to shake.
1. Bushings - check to see that they are not worn. Looks for cracks, and excessive play)
2. Angles - this angle should be the same as your draglink. Use an angle finders you can get at sears to determine this, don’t just eye-ball it.
3. Bolts – Make sure all bolts are tightened down to spec (some lift components have a different torque spec then)
Check the Axle, your mounts may be worn
1. Check the axle mount. Here is a good write up on a wallowed out bolt hole
http://www.jeepin.com/features/trackbarfix/index.asp
2. Check your Universal joints, a binding or lose U-Joint can cause DW
3. On the frame end if you still use the conventional Tie Rod End or (TRE) make sure that there is no play in this, as play can cause DW.
4. Look/Check for worn/torn boots on ball joints/tie-rod ends.
Check your Tires
1. Out of balance tires can cause shaking in the front end, which can lead to deathwobble.
2. Make sure all of your lug nuts are tight, (Sounds elementary but it happens to the best of us)
Check your Frame
1. Small cracks in the frame can cause the steering box to feel loose, Shaking from DW can only make this worse. 33’s and larger should have some form of Steering box brace, or frame brace in.
2. If you have upgraded your frame mount, make sure its cranked down nice and tight. (best to use an impact gun)
3. A busted Frame Mount can cause play in the front end causing DW (Keep a watchful eye on the welds as welds in sheer can break over time.
Make sure you have a good alignment
1. After you get an alignment done, have them print out the numbers for you. An XJ should have a 7* positive caster angle. A lifted XJ can’t always have that high of a number because the pinion would become out of alignment with the front driveshaft. Pinion angle takes precedence over caster.
2. Make you sure you go to a place that will adjust the caster if necessary (either by shims in the frame side of the LCAs, or adjustable LCAs).
The more adjustable parts the easier it is to tune in your suspension.
1. Adjustable Track Bar
2. Adjustable Upper and Lower Control Arms (upper ones above 4†of lift). Not only are they adjustable, but they are stronger.
Things to remember:
1. A Steering Stabilizer (SS) is not a quick fix for DW.
Entire list of everything that can cause deathwobble:
-Front tires out of balance
-Front alignment out of spec
-Loose track bar
-Worn track bar bushings
-Worn track bar end
-Need adjustable track bar
-Bad bushings/joints in control arms
-Worn/damaged steering stabilizer
-Worn/damaged shocks
-Worn/damaged tie rod end
-Bad U Joint
-Bad ball joint
-Loose frame mount
-Steering box looseness
-Need drop pitman arm
-Driveshaft(s) not balanced
-Bad front hub assembly
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Steering ...Death Wobble...front suspensions on our vehicles... superposition principle ... elastic elements, viscous damping (steering damper and shocks) ... critically damped, ...the tire is moving... answer a question...Everybody got all that? ...Caster ... deathwobble.. front hub assembly
yeah... what he said ;D
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yeah lol. thanks im gonna read it a little more thurough tomorrow when i have more time but it deffinately looks helpful.
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Just an FYI, but I'm not even running a steering stabilizer on my TJ right now.
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I'm not running a stabilizer either. and even though toe in needs to be adjusted after changing a tie rod end I still do not have any DW. but I run leaf spring so it's kind of hard to change the geometry.
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maybe the adjustable trac bar that came with my lift is a POS i want to get the upgraded one with an eye on each end. plus i havnt got a good allignment on the jeep yet since i put the lift on it. every time i get money i buy something for the jeep instead of fixing things, lol hopefully the alignment will help a lot
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If you haven't done an alignment since you lifted your Jeep then your toe is way off and that is at least one thing that is contributing to your deathwobble. An alignment is necessary after a lift or you will almost always have DW.
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yeah im planning on doing it next weekend or hopefuly sooner since ill finally have some extra money
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so i just went and got an allignment and i have the new rustys hd trac bar and frame mount and the hd tie rod with new ends and i still get death wobble as soon as i hit a bump doin like 35-40. im so aggrivated. does anyone think maybe my lower control arm bushings could be the cause of this??? cause im still runnin stock......
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Lower control arm bushings can cause it, but they are usually not the first suspects. When you put in your new track bar did you check the axle mount? I have DW right now because the bolt hole on the axle side of the track bar is wallowed out and allowing almost 1/2" of play in the track bar. How old are you wheel bearings and ball joints. Have you lifted a tire and tested for play there? Wheel bearing units and ball joints always lead to death wobble if they are bad.
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yeah i tried to shake the wheels and there tight. and the trac bar mount on the axle is good too.. but i ordered some fixed lowers for the front and im gonna see if that helps
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100% agree that the problem is not the steering stabilizer. I solved the death woble in my YJ with a tie rod flip kit from Goferit. My steering geomety is pretty close to stock with the flip kit and a drop pitman arm. Good luck.
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check your trac bar bushing... my zj jad wicked deathwobble cuz i blew out the front trac bar bushing.. the alignment was spot on and everything else was perfect, just give her a lil nudge from the driver or passenger side and see if she shakes a little
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finaly fixxed the death wobble i believe.. i had it up to almost 50 today and no death wobble.. i changed like all the steering parts in the front and it did nothing. turns out it was my sway bar bushungs and the CHEAP disconnects i had on the front. changed the bushings and got JKS disco's and she rides pretty nice now. im so happy, now i can take her places faster than 25MPH
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Death Wobble is also related to how parallel the track bar and the tie rod are. If you look at a stock Jeep they are pretty close to being parallel. When people lift their rigs, these angles change and contribute to death wobble. Like Kirk said, do a tie rod flip, get your rig professionally aligned, and changing out your bushings should cure it. Adding the steering stabilizer will make control minute wobble that you probably won't be able to feel.
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Donty you mean the track bar and the drag link? If either of those were paralell to the tie rod I think hed have very serious issues
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Donty you mean the track bar and the drag link? If either of those were paralell to the tie rod I think hed have very serious issues
douce why do you gotta be a douche lol i have been wanting to say that for a while sorry... but yea your right there would be a problem but he probably just made a mistake in the typing
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Just making sure cuz that is how I have always understood it.
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oh i figured as much but i just need a real excuse to say that but back on the topic of death wobble, i had that problem with my zj and it was NOT the sway bar or links i mean hell, i drive with my disconnected sometimes, like after a ride, and i can take her up to 65 no problem. i went through and checked all the bushings but one and it was the axel side trac bar bushing being close none existent. in the future my friend just check all of the bushing then if there is still the problem its something alot worse.
p.s. its nice to know im not exactly the only zj here
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yeah apparently its not totaly fixed.... i got the shit this morning right over 40 mph then i got it on my way home from fishin doin 30 when i drove over a storm drain.. its really starting to piss me off. the jeep is beating me damnit i cant win. so i ordered a drop pitman arm to lower my steering angle maybe that will help i donno
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Normally, the rule on the drop pitman arm is that you don't need it unless you are over 4" of lift or you have installed a drop track bar mount. Same basic principle from what's been stated earlier. The track bar and drag link need to be on the same plane.
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well im runnin about 5 inches of lift right now... but i dont have a trac bar drop bracket.. i just have rustys trac bar and frame mount... i really need to get this thing figured out.. its already held me from going to the last car show and the last trail ride. i want it fixed so i can go wheelin with all you guys. shes good in the woods just not on the road...
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could it also maybe have to do with the 32x11.5-15 super swamper tsl sx bias ply tires i have on it???? they took a really lot of weight to balance and they suck on the road.?
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could it also maybe have to do with the 32x11.5-15 super swamper tsl sx bias ply tires i have on it???? they took a really lot of weight to balance and they suck on the road.?
I was just reading through your posts to make sure that tire balancing had been addressed and it doesn't look like it has. When I had my Cherokee I had developed some really bad death wobble right after a trail run. Everything in the suspension and steering looked fine so I decided to have my tires rebalanced and found that I had ripped 2 wheel weights off on the inside of the tire so I couldn't even see that they were missing. They rebalanced the tires and deathwobble was gone. Because of what we do we chunk up tires and slice them quite often and balancing may be needed quite often unless you're running balance beads or something like that.
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yeah cause the weights go like almost half way around the rim its rediculous. so i donno i might chuck the tires and get some new different 33's with a radial tread more road friendly like some bfg mt or something
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yeah cause the weights go like almost half way around the rim its rediculous. so i donno i might chuck the tires and get some new different 33's with a radial tread more road friendly like some bfg mt or something
That's not a bad idea. Bias ply tires are difficult to balance and they don't run near as smooth as a radial. Your DW could very well be tire related.
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i really hope so man, im ordering a new set of 33x10.5-15 bfg mt km2's right now there only 168$ each i just hope there a good tire
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i really hope so man, im ordering a new set of 33x10.5-15 bfg mt km2's right now there only 168$ each i just hope there a good tire
One of the best....
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sweet i got them all ordered up
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Why 10.50 not 12.50?
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less weight and i think narrower tires cut through the mud and snow better myself
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I would love to find a 35x10.5 rather than the 12.5 myself. The 10.5s track much better in slushy snow and and have less of a tendency to hydroplane in standing water.
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They make the km2 in a 35x10.5x15 i guess my road tires are going to be km2's so i can run my turbine wheels they won't stick out as far and not require a massive flare to cover them and they will do better in snow and Km2's are an awesome tire
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Donty you mean the track bar and the drag link? If either of those were paralell to the tie rod I think hed have very serious issues
You are correct....My bad... :-[
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swamper makes a few tires in a 35x10.5