bump death wobble - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 25 Old 12-24-2007, 10:33 AM Thread Starter
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bump death wobble

stated getting death wobble at low speeds when I hit a bump with only one side of the JK. Before I start going over everything I want to get a census.

What caster angle you running?
What toe in?
Did or have you get any death wobble?


I noticed it and was not able to get under there to look for a few days and found a loose upper control arm bolt (figured t would be something loose) test drove, still did it. Figured maybe I messed up the balance or knocked a wheel weight off caused/causing the loose bolt, balanced today and rotated and still same thing.
Figure get some of you guy's info before I crawl under it and have a baseline for adjustment.

4" superlift, 35 MT Claw radials.
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post #2 of 25 Old 12-24-2007, 10:55 AM Thread Starter
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I got 1.6* and 2.3* caster off the flat-top of the knuckle.

Nothing "appears" to have shifted or moved since the installation of the lift 6ish months ago
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post #3 of 25 Old 12-24-2007, 12:16 PM
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I've been messing with pinion angles the last week, but my caster is now about 1.5. That is about as low as I can go before the steering gets too light. I've been down to 0 and the steering is scary light, but no bump steer or death wobble.

FWIW These are my front end angles.

Driveshaft Angle: 10.1
Pinion Angle: 4.5
DS/Pinion: 5.6

I do have the Poly Performance high steer drag link and their track bar bracket. After installing them, I noticed a definite reduction in bump steer, to the point it is pretty much non existent.

I'd check all the bushings on the control arms for any that are worn or loose. I'd also check all the rod ends on the drag link and tie rod. As the problem appeared with no changes, I'm guessing you have something worn somewhere. I wore out a couple of rod ends on the drag link before going high steer.

Also check the track bar, I wore out several heims on my adjustable track bar.
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post #4 of 25 Old 12-24-2007, 01:16 PM
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I'd also check the front ball joints at the knuckle. We had some go out all ready on one of our JK's.


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post #5 of 25 Old 12-24-2007, 03:37 PM
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Track bars and control arms need to be snug too. Particularly in back.

How's the shocks and springs?

Tire pressure?

Tire balancing?
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post #6 of 25 Old 12-26-2007, 06:55 AM Thread Starter
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Tires were balanced fine (waste of $30 but ruled it out) I increaced the caster as much as the eccentric cams on the lowers will do and it "seems" to have gone away.
Nothing else was loose besides 1 upper link bolt, EVERYTHING was tight and all steering joints fine as well.

Maybe its time to save up MORE cash after I save for bumpers and get some adjustable lowers
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post #7 of 25 Old 12-26-2007, 07:06 AM
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Quote:
Originally Posted by usmcdoc14 View Post
get some adjustable lowers
If you are just going to do one set, then do the uppers.

I'm not sure why having a low caster by itself should introduce a wobble. I've had mine down to zero and while the steering feels dangerously light, it does not introduce any wobble.
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post #8 of 25 Old 12-26-2007, 05:55 PM Thread Starter
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Quote:
Originally Posted by PhilD View Post
If you are just going to do one set, then do the uppers.

I'm not sure why having a low caster by itself should introduce a wobble. I've had mine down to zero and while the steering feels dangerously light, it does not introduce any wobble.
don't know. I went over every bolt in the suspension, checked for ball joint and steering play and other than that one upper bolt being LOOOSE it was the only thing I changed and it appears to have gone away.
I will have to ask Bev if its still doing it as she drives the JK to work until I do the engine swap on her waggy and fix the exhaust leak so the MPGs don't suck
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post #9 of 25 Old 12-26-2007, 06:31 PM
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Quote:
Originally Posted by usmcdoc14 View Post
don't know. I went over every bolt in the suspension, checked for ball joint and steering play and other than that one upper bolt being LOOOSE it was the only thing I changed and it appears to have gone away.
A loose control arm will definitely cause some wobble issues, so that was likely it, hopefully.
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post #10 of 25 Old 12-28-2007, 09:03 AM Thread Starter
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Quote:
Originally Posted by PhilD View Post
A loose control arm will definitely cause some wobble issues, so that was likely it, hopefully.

wheeeeeee feeling a slight "clunck" sound. seems my lower track bar mount may be wallowed out. That bolt is shifting around a little.

Time to pull that off and inspect.
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post #11 of 25 Old 12-28-2007, 09:17 AM
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Quote:
Originally Posted by usmcdoc14 View Post
wheeeeeee feeling a slight "clunck" sound. seems my lower track bar mount may be wallowed out. That bolt is shifting around a little.
Had that happen on other vehicles, the quick fix is to drill a hole in a piece of plate and weld it on the bracket.
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post #12 of 25 Old 12-28-2007, 10:13 AM Thread Starter
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Quote:
Originally Posted by PhilD View Post
Had that happen on other vehicles, the quick fix is to drill a hole in a piece of plate and weld it on the bracket.
Thats what I am going to do if the lathe at work was working I would drill out the trackbar holes and make some stepped plugs to weld in.

But I am lazy today
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post #13 of 25 Old 12-28-2007, 12:15 PM Thread Starter
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I did both the upper and lower. Holy hell is the INSIDE lower a pain to get at and weld. There are some Sahweeeet bugers inside there where I was welding by "feel" and could not see a damm thing
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post #14 of 25 Old 01-13-2008, 11:09 PM
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whats going on guys im new hear but im on another forum. i have had this "death woble" for sometime now. i put a rough country 1 3/4" lift on there just the spacers and 8000 hydro shocks, everything was fine for about 3 months then i went and had an alighment done and the SS for some reason sears un-did the u-bolts that hold that bracket on. i got the woble real bad the next night 2 times in a row, went home found out that it was lose took back got my money back had anthor alighment done at NTB and they had said it dosnt even look like there was an alighment done. so i had it done and it came back, i had my tires balanced and roated 2 times in the last month about 3 weeks apart also, so i took the lift off and just left the 8000 hydro shocks on there, came back again, so took it to have it looked at again and the guys at NTB said the SS was bent/the seal was gone/ and there was water inside of it, so i got a new one at napa and put it on torqed it down, and it seemed to be fine drove down I-55 two nights ago nothing not a shake or anything, then tonight i was driving down this road doin about 55-60 right in there and it felt like it wanted to do it again so i drove back down the road and it did the same thing only felt like it then it just stoped and didnt come back. drove down it again alil later and it started to want to do it again and then didnt and it was fine. im going to be putting on the stock shocks prob tommrow of tuesday, but i have no idea what it could be? any suggestions thanks guys dave

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post #15 of 25 Old 01-14-2008, 05:58 AM
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The steering stabilizer should have nothing to do with death wobble. It may mask a little bit of wobble, but will not cause the wobble.

Likewise with the shocks, even if they are blown (which you would know) they should not cause a wobble.

You'd think if there was a bad steering or suspension component the alignment shop would have picked it up.

First thing I'd do is make sure the track bar and control bushings all look good, then make sure they are all torqued down correctly.
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post #16 of 25 Old 01-14-2008, 10:55 AM
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Also check the ball joints, specifically the lowers, they were toast on both of our JK's and Curries as well.

Here are the factory alignment specs, I dont know if the alignment shops would have this data yet:

Caster: +4.2 deg, +/- .5 deg
Camber: -.25 deg +/- .37 deg
Total Toe-in: +.20 deg (+/-.03 deg

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post #17 of 25 Old 01-14-2008, 11:13 PM
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this is the weird thing after i replaced my SS im able to go 55 just fine and not have a woble like i would have before. it felt like it wanted to happen twice but it never did, and i was able to get up to 60 and then 65 and it was fine.

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post #18 of 25 Old 01-15-2008, 06:29 AM
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Quote:
Originally Posted by dave piry View Post
this is the weird thing after i replaced my SS im able to go 55 just fine and not have a woble like i would have before.
Like I said a steering stab may mask the problem, but is not the cause. If that is all you changed, then the problem still exists, and your new steering stab is just masking it.
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post #19 of 25 Old 01-15-2008, 06:13 PM
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Roadforace balancing the tires were a huge help when I got it. It took 3 attempts of balancing. 1 time non-roadforced and then twice roadforced.

I then found a few incorrect torquing of some of the bolts.

I then un-installed the front track bar. Torqued off bolts and lowered the vehicle so the weight was on it and re-torqued.

Since then it's beeeeen sweet.

No more wobbles, no shimmy nothing.
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post #20 of 25 Old 01-16-2008, 07:26 PM
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Quote:
Originally Posted by usmcdoc14 View Post
I got 1.6* and 2.3* caster off the flat-top of the knuckle.
That is probably not enough caster. Also that is a pretty big difference left to right. The Jeep will be a little twitchy like that.

I have seen another Superlift equipped jeep with this issue. Did you put in the custom eccentric bolts?

Also remember that coil sprung jeeps are not like the old leaf equipped vehicles. Don't set it to 6-7 degrees or you will get excessive wobble also. I have had best result in my TJ at the minimum spec for the vehicle (as little as recommended by the factory)

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post #21 of 25 Old 01-17-2008, 01:15 AM
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every rig is different. the cure for DW in my ZJ was 6-7* of caster.

then i changed out the factory steering for a Teraflex High Steer kit. no more DW. I drove it with no front swaybar or steering stabilizer for about 3 months with no hint of DW. it wandered a bit... but no shimmy. put the caster back to around 3-4* when i installed the long arms. still no DW... but it does wander more.
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post #22 of 25 Old 01-19-2008, 03:36 AM
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well i checked the bushings nothin wrong, checked for lil stress cracks nothin, checked the tourqe everything was tight idk what else to do

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post #23 of 25 Old 06-08-2011, 08:29 AM
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Quote:
Originally Posted by PhilD View Post
I've been messing with pinion angles the last week, but my caster is now about 1.5. That is about as low as I can go before the steering gets too light. I've been down to 0 and the steering is scary light, but no bump steer or death wobble.

FWIW These are my front end angles.

Driveshaft Angle: 10.1
Pinion Angle: 4.5
DS/Pinion: 5.6

I do have the Poly Performance high steer drag link and their track bar bracket. After installing them, I noticed a definite reduction in bump steer, to the point it is pretty much non existent.

I'd check all the bushings on the control arms for any that are worn or loose. I'd also check all the rod ends on the drag link and tie rod. As the problem appeared with no changes, I'm guessing you have something worn somewhere. I wore out a couple of rod ends on the drag link before going high steer.

Also check the track bar, I wore out several heims on my adjustable track bar.
Phil can you tell me with your PP trackbar, do you have a lift on your Jeep? I am trying to see if the PP bracket can be used on a JK with no lift (the part description says it's compatible with 3" lifts and higher, so I wasn't sure if that meant the part also works with JK's with NO lift). Thanks!
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post #24 of 25 Old 06-08-2011, 08:36 AM
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Quote:
Originally Posted by notherone View Post
Phil can you tell me with your PP trackbar, do you have a lift on your Jeep? I am trying to see if the PP bracket can be used on a JK with no lift (the part description says it's compatible with 3" lifts and higher, so I wasn't sure if that meant the part also works with JK's with NO lift). Thanks!

It will not work on a JK with no lift, reason is: you MUST use a 3" or taller bumpstop spacer with the track bar relocation bracket and flipped draglink. If you look at the factory track bar at the axle, the top of the track bar busing is shaved to clear the frame, it comes that close at full bump. we raise the track bar 3" so you must limit the up travel by 3" to prevent the track bar and draglink from contacting the frame at full bump.

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post #25 of 25 Old 06-08-2011, 08:51 AM
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For JK axles, we like to be in the 4.2 to 4.5 degree of caster range.

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