Calgary Jeep Association
4x4 Related Groups => Tech Talk => Topic started by: AV.NINE on February 12, 2009, 09:27:24 PM
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I installed my 5" skyjacker kit with 2" spacers, both trackbar brackets and extra supports, everything is tight as hell.... BUT seems like when i slightly turn left at a certain speed the dreaded death wobble comes into play, big time.
Everythings tight, i do have the "stock" steering stablizer on... could that be the issue?
any advice is appreciated.
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Steering stabilizer is not the cause of death wobble... it can be a band aid solution in some situations but your best bet is to find the real cause.
A wobble caused by a turn makes me wonder if your unit bearings are OK... or your ball joints. Typical death wobble is caused by a loose track bar or bad control arm joints. Hitting a bump will cause the suspension to start to ocillate and making you think you're about to die. Once death wobble starts the only cure is to slow down so the ocillation stops.
What are your exact symptoms?
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Slight left turn around 60-70 and steering wheel shakes back and forth, jeep shakes. Ive had the deather wobble before with a loose trackbar, same thing. Happens like once very 2 days. Its an 08, so I would hope its not the wheel bearings or ball joints. just rolled to 20K.
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Bnine is the death wobble guru around here. Hopefully he can jump in and offer some suggestions.
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Are your tires cupped?
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Yes, I stuck them on the rear. (i got them used, already cupped from being on his jeep, same lift)
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And they're 37's, if I recall correctly.
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yup!
Should mention, I got a wheel alignment after the lift.
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Copied this from another site. Has very interesting info on the subject.
we all expirience it sooner or later, while surfing across the net i found this. It was writtne by Jim frens the owner of nth degree mobility (now works for AEV) he was a engineer at chrysler and knows his isht.
What’s the deal with death wobble / shimmy?
A doctoral dissertation could be done on shimmy (aka ‘Death Wobble’)…It is not so much a ‘design flaw’ but rather an engineering challenge that has yet to be absolutely overcome in suspension design…and we off-roaders just have to live with it more than the rest due to the fact that we do “all the wrong things” to our rigs and basically invite shimmy to happen as a result. Shimmy continues to defeat even the best full-compliance vehicle dynamics modeling programs (Jeep uses ADAMS). The phenomenon is pretty well researched, but it plagues even the factory at times…Jeep almost had to delay/cancel one model launch because it developed a shimmy problem during the last run of prototype parts – only 3 months before launch. We had to ‘tweak’ four things about the suspension to make it go away: reduced lift height to +0.6” from the traditional 1.0”, change durometer of front LCA bushings, re-valve steering damper, and change nominal caster spec…”traditionally”, the last two are the primary things that affect the risk of shimmy, but another major player is front tire balance…they must be *dynamically* balanced (i.e. weights on both rim edges, so the wheel/tire assy is balanced in all planes, not just one).
So here’s the ‘techno-speak’ dissertation on shimmy: It is an imbalance of the gyroscopic forces generated by the spinning front tire/wheel assys…when the ‘setup’ of the front end is ‘vulnerable’ to starting shimmy, it happens due to an asymmetrical force (i.e. one tire hits a bump that the other doesn’t) or also it can happen when the bump-force is not even side-side (in this case it usually happens at higher speed due to say a ‘swell’ on the highway). The problem is worst with wheel-wheel tie-rods (which is why the TJ and most late Jeeps use the Haltenberger linkage – aka ‘inverted Y’ design) because the tires can ‘crosstalk’ directly to each other. The larger/heavier the tire/wheel assy’s are, the stronger the inertia and thus the worse the shimmy can be if it starts….of course a damper is the most direct defense once shimmy starts, but what you *really* want is for it to not start in the first place. For that, you have to look at the ‘free-body diagram’ of the forces that can influence the stability of a spinning front tire/wheel assy. The key for shimmy issues is the distance between the ‘center of tire contact pressure (CTCP, which is not directly below the hub due to ‘pneumatic trail’ – it’s actually further back.) This is the effective center of downforce of the tire’s contact patch when it’s moving/rolling) from the ‘steering point’ (the point where the steering axis intersects the ground plane). If you leave the caster setting at the factory spec of 6-8 degrees while increasing tire diameter from 27-28” to 33-35”, then you’ve effectively *increased* this distance (and therefore the imbalance force it can generate), while at the same time you’ve increased the mass that drives this force (the larger/heavier tire/wheel assy), so when things get to shimmying, they REALLY shimmy! So…what to do? If you’ve followed this far, the answers are easy to ‘guess’, but should be divided into ‘preventative’ and ‘band-aid’ fixes:
Preventative (i.e. will reduce the likelihood of shimmy, in guessed order of empirical relative effectiveness):
1) Keep wheel/tire mass low (i.e. run stock-sized-or-close tires and/or aluminum rims – both of which are likely unacceptable to a real ‘wheeler)
2) Keep CTCP – to – steering point distance short by running stock-ish diameter tires (also not acceptable)
3) Reduce the CTCP – to – steering point distance by reducing caster (moves steering point back towards CTCP)
4) Run radial tires!
5) Dynamic balance the tire/wheel assy’s (weights on both rim edges)
6) Avoid direct wheel-to-wheel tie rods, or if so, have deliberate ‘compliance’ in the tie rod (i.e. not too stiff, but steering feel/precision will suffer)
7) Maintain high lateral stiffness via proper trackbar design and bushing rates (i.e. no non-preloaded urethane bushings and hollow-tube t-bars!)
Tune front control arm bushings on the ‘stiff side’ (i.e. high-ish durometer…TJ uses stiffer LCA bushings than XJ for example, due to trackbar bracket stiffness differences, etc.)
9) Drive slow and/or don’t hit any bumps!
Band-aid-type fixes:
1) Heavy-valved steering damper (helps a lot if tire/wheel mass is 100# per assy or less. Multiple dampers will help with heavier setups, but too much damping will limit steering response time)
2) Match all compliances together to allow drastic violation of above guidelines (i.e. apply a lot of engineering to the bushings and linkage stiffnesses while screwing up the other engineering parameters…)
…so what’s the “Bottom Line”? It’s this: the stock caster spec is NOT the appropriate spec for your lifted Jeep running bigger tires. For 33” tires, I recommend about 5.0 degrees, and for 35” – about 4.0 degrees.
Ultimately your issues (or not) with shimmy will be determined by how well your rig is ‘set up’ either by you or your shop…so the main thing we’re doing is putting some watered-down version of the above in our product instructions (i.e. a new caster spec based on tire size), but also we’ve made sure that the lower caster setting is in the middle of the adjustment range so you have a chance of setting proper caster (which I’ve found isn’t possible with some lifts), and this will help you understand why we’ve designed the front trackbar as a factory-type one-piece solid forging with high-durometer, rate-plated bushings and a stiff trackbar bracket/brace.
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Next step Im going to try and shouldve done originally... Beefed up steering stabilizer and tire balance. Maybe help with the cupped tires.
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The above post has some ok advice. Ignore the caster BS, its web wheeler rhetoric.
The first thing to do is shake test the front end. Have someone cycle the wheel, motor off, from 11-1 oclock. Find out what has movement.
More then likely its your track bar.
Joints an bearings should be fine with that low km's. Watch for movement between the dust sheild and rotor just make sure on the wheel bearings.
Worse case is that your CA bushings are to weak to handle the weight and quality of the rubber you are running.
Shortest fixes for that is better rubber, hydro assist, or upgraded suspension.
You have two choices, run better quality and or lighter rim and tire combonation, or spend the money strengthening your suspension and steering to handle the forces fo the big rubber.
For now, you should be able to dial it out with a jeep as new as yours.
Good luck
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I got a couple Jk things for you to take a look at.
1) As you have a Sky Jacker lift check your front trackbar bracket. A lot of JKs have had them go bad VERY quickly, some have even failed with the factory 32's, and no wheeling. If it's starting to tear or break you should see the lines/wrinkles/tears starting. The Skyjacker kit also uses a bracket extension on the front bracket (sure I've mentioned this somewhere on this board before, having deja vu...) which is like throwing a snipe on something. It multiplies the forces exerted.
2) Another one to check might be the tie-rod. I haven't dinged mine yet, but apparently these stock ones fold like cheese slices. Rock Krawler makes a forged one, but you've gotta get the moog end yourself. Sure that could throw something out, but I would think that would just be wonky all the time. Dunno enough yet about suspension/steering/alignments to say. Sure Bill can answer this for you.
What else have I heard about d-wobble and sky jacker.....think think.
3) Oh, have a dropped pitman arm? Bet you kit didn't come with one. At the 4" height level you should be thinking that or something like the TeraFlex drag-link flip kit. I think maybe Poly Performance or Rock Krawler make something similar. I'll probably F this explanation, so I'm poaching this link (all these kits do a similar thing) http://www.jk-forum.com/showthread.php?t=53724&highlight=teraflex+flip (http://www.jk-forum.com/showthread.php?t=53724&highlight=teraflex+flip).
That's all I got for you man. Hope you get it worked out.
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Will check all posted, thanks guys. Yes I have a drop pitman arm bracket. Will post up right away.
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Your symptoms sound a little different than mine were but there's no harm in checking. My front driveshaft was bent and caused vibration and shaking at different speeds. Lift up the front end and spin the tires while looking at the shaft. I had spent about 800$ on replacing various components before noticing the bent shaft.
Good luck.
Dennis
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Did you re-center your steering wheel. I know if its off, you will get the death wobble like crazy. Here is a link.
http://project-jk.com/jeep-jk-write-ups/basic-do-it-yourself-jeep-jk-wrangler-front-end-alignment
Your stock steering stabilizer should be fine with 37", aftermarket ones only hide the problem, they don't fix it.
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every time i've encontered death wobbles on a few different vehicles i just changed the steering stab and cured the problem.i've had to change brand new steering stab also because they were faulty from the factory
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Front track bar mount came loose. Barley visible to the eye, but after I installed my procomp SS, the death wobble got worse and worse. Till today I couldnt drive 50 M without it shaking to death.
Of coarse, I was in Red Deer without my garage or tools and its saturday so NOTHING was open..... the only place I found open was.... ugh.... toyota....and canadian tire.... so toyota it was.
But they were nice and tightened my bolts and added locktite for free! Drives good now, just need some upper adjustables to correct my castor.
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so in the instructions for the lift you installed the last thing was to road test and re-torque everything after 100-500kms. and then re-torque everyhting every now and then. once you've modified these vehicles the maintenance goes up. but its a small price to pay. next time you feel the death wobble you'll know where to look. good build up on the jk by the way:)
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Temp solution. Its back big time... Everything is tight that I can see. The angle between the trackbar and drag link seem fine... Still haven't balanced tires, but man am I sick of this wobble. On the highway its fine but I can't go 100 meters in town with it.
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I put on the stock stabilizer and no more death wobble.... WTF!?
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Death wobble is a result of a certain amount of force applied to the suspension, and the ability for those forces to go into a resonating harmonic frequency.
Very small changes in things like dampeners, tire pressure, tire balance, etc etc can make it recede for a short time.
The problem is still there, its just held off for the moment.
Your best bet is to get someone that really knows what to look for take a look at it for you. Not necessarily a shop either. Very few shops are actually good at diagnosing and correcting death wobble properly.
There is something weak or way out in your front end. The fact that small changes in the stabilizers is making it come and go confirms it.
Are you in red deer? Try to hook up with Brink. He should be able to spot it for you.
If you are in calgary, get Dougy to bring you by. I'll pick it out for you.
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Vibrations that you can start at a certain speed but can be accelerated through are 99% always tires out of balance
Balance the tires
Steve
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I've put truxus MT's on a couple of different customers vehicle's and they always take stupid amount of weight. and have even checked the balance of the rim without a tire on it. Just my opinion but for what the truxus cost now, they take way to much weight and should be manufactured better. My thoughts are that your tires are wearing unevenly and causing them to go out of balance. For the same or less money you can throw a set of mickey Ts, or cooper STTs or a number of other better brands of tires on when it comes time to replace truxus MTs. I've found that even with worn bushings and less than par track bars, if a vehicle has a proper alignment and balanced tires, you shouldn't get DW.
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Unit bearings are about 100 to 150 takes me about an hour to change both sides
I still think you need to balance the tires
If I'm reading what you posted earlier correctly the wobble occurs about 80 kph but above and below that its not there If this is correct balance the tires before anything else (if balancing doesn't do anything for the wobble , you buy the unit bearings and I'll change them for you)
Steve
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If you go to a shop that sells tire products, they'll have a chart that goes by the size of tire that you're running telling you how many ounces of balancer you need. Running them on a balancer doesn't work.
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you can try air soft pellets, but for the twenty buck or so, use "couteract" balancing beads. If you're going through the hasle of breaking the bead, might as well use the stuff thats made for balancing. It comes in different size(weight) packages.
1. Break bead
2. Open package
3. Throw bag with stuff into tire
4. Reseat tire and drive, bag breaks open and you have balanced tires.
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balance the tires first then ad the airsoft pellets or balancing compound one the stuff is added to the inside of the tire the only way to balance the tires is to remove it
The manufactures of balancing compound recommend you balance the tires first then add the compound so that as the tires wear it keeps them in balance
below 40kph the compound will not help in fact it might hinder the tire is not spinning fast enough for the product to spread out so you might end up with a major shimmy at low speed if the compound settles at the heavy side of the tire
That said go get the tires balanced and see if the wobble gos away if it dosen't it could be time for unit bearing or ball joints or tie rod ends or track bar bushing
start with the cheapest and go from there
the other option is if you could borrow a set of wheels from someone else and put them on yours and see if the problem go's away then you know its the tires
Post a vid of the end components with the jeep sitting on its wheels with the engine off and someone rocking the steering wheel from 11 to 1 and i'll tell you if you need front end parts
Steve
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i powder balanced my bias-ply swampers and put a new bearing in my frontoutput shaft in t-case(first time actually pretty easy,and mine was halarious so messed)and was a WORLD of difference.and thats with my track bar being shot....and bias ply tires...I dont know enough about all of the science but know for sure a lot of small little issues can create super death wobble. i may have"band aided"the real problem but seemed to have cured it so far? just a thought after reading through the thread and parts about tires/wheels,
98 tj retrofit rubicon 44's on 36 bias swampers.
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i put airsoft in my 36in tsls it worked great, did it last year and all is still good. it made a huge diferance, now i can cruse down the highway with out my jeep shaking appart 8)
i think the Dynabeads is probly a bit better way to go.
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the airsoft re ballance every time you take off from being stoped, where i think the other stuff uses static electricity to stay stuck to the inside of the tire so they dont have to rebalance every time you take off.
i never realy reserched this and am just going off what im told. ;)
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Stop the madness. Pat, your front end is worn out, and Trxus are tough tire to balance. These guys talking about pixie dust and the other balancing gimmicks arent stopping to realize that they are a bandaid, no more effective then a new stabilizer.
The only thing the trxus does in regards to death wobble is exagerate sooner then a smoother running tire will.
regardless, your wobbles have SFA to do with your balance, unless the tire has blown a belt, gone out of round, or your rim is bent.
I've said this 100 times on this site, and fixed as many for nearly as many times. DEATH WOBBLE IS NOT DIRECTLY RELATED TO TIRE BALANCE OR WHEEL ALIGNMENTS.
Pat, if you are experiencing early onset of death wobble, bring your jeep over and I will show you how to diagnose it.
I've done this for 50 some members on this board, and solved this issue at least two hundred times.
Not once have had them balance their tires, get an alignment, or fill their rims with pixie dust.
Sorry if this post is a bit aggressive. People getting mislead on steering issues via web wheeling is a a bit of a pet peeve of mine.
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Bill he said he has a wobble at 80 but not 90 thats not DW is it ?
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http://www.fourwheelstampeders.ca/forum/viewtopic.php?f=76&t=3590
For your tire balancing information. I'd probably go the BB idea over the packaged ones. Even with the valve stems replaced with special stems I've still had a few issues when airing down.
If it's a death wobble situation. Get rid of it for good by selling the TJ and pick up a CJ. Only wobble you have then is from lose wheel bearings. ;)
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the airsoft re ballance every time you take off from being stoped, where i think the other stuff uses static electricity to stay stuck to the inside of the tire so they dont have to rebalance every time you take off.
i never realy reserched this and am just going off what im told. ;)
sorry to clarify i was onlt talking about balincing tires not geting rid of DW. BILL :P
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i'd just dump the trxus............ the ones on my ZJ shook worse than my iroks...................
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Well if I had a boatload of money *and* hadn't won a second set, I'd consider it. Oh and that they perform fantastically other than balance and weight issues.
tell ya what, when you have a boatload of money, i'll be the Skipper of that boat anytime!
i did the pixie dust thing....... didn't work worth a poop. went through unit bearings every 3 months............. so i bought a DD instead of continually fixin my trail rig/DD. they were decent enough trail tires but felt like swampers on road....
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Sell the set of truxus that you won and get a decent set with the proceeds, when your present set is worn out.
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Well now that I've had pixie dust in all 4 tires (quite a bit too)... and had people check the front end ... and been offroad etc., I decided to figure out which <family site - deletions performed> tire despite all appearances of being fine has a problem. Since a fellow in a truck the other day just about fell out of his truck staring at my right front wheel when the hop started happening, I started there.
Added pixie dust to the spare (slow leak) and put it on the right-front. WOW... the bounce/wobble is gone and it's WAY smoother than before... oh and I've been getting much better mileage even with the bad tire on, so I believe in pixie dust, but it won't fix a bum tire or suspension problems. I figure hundreds of thousands of kilometers of testing with commercial trucks is a pretty good indicator.
If I remember, I'll post an update when I have more time on these tires with the pixie dust in.
I hate to say it but
I TOLD YOU SO
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I hate to say it but
No you don't.... you live to say that!!
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Sell the tires on kijiji. And with the amount that the intercos have jumped in the last year or so, you shouldn't get soaked on them. For a good go everywhere tire consider a MTZ. I was surprised at how well they work on ice.PM
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Bear in mind that you're not limited to running tires exactly the way that they came from the factory. So far I've been very happy with the results from siping my BFG Mud Terrains.
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Most tire places seem to view siping as some sort of strange voodoo. They don't really want to talk about it and certainly don't want to do it.
I found a place that would sipe my factory tires for me, even after I had driven on them. Their only request was that the tires were relatively clean and not too worn.
More to the point the manager of the place managed to convince me that he was confident in the work that his guys would do. His comment to was "If I screw up your tire, I'll buy you a new one."
I'll PM you the location and price.
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You should just post the location so we all know who does it and backs their work with a guarantee like that..
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They're not someone that has sponsored the club in the past, so I don't want to step on toes. If it's okay with the execs, I certainly have no issues posting the details - they did right by me.
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They're not someone that has sponsored the club in the past, so I don't want to step on toes. If it's okay with the execs, I certainly have no issues posting the details - they did right by me
Nothing wrong with sharing info on a company that does good work . ;D
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Nothing wrong with sharing info on a company that does good work . ;D
Kewl :)
I got them done at Kal Tire at the Chinook center. $30 per tire. In and out in two hours, and they've been great since (that was about nine months and 25,000 km ago). No chunking, no issues with side lugs, no strange wear patterns - although I do rotate regularly.