Axle Upgrade/Minimum Scrub Radius

JJ151

JJ151

Member
Installed brand be Dynatrac XD60s a couple weeks ago and can’t seem to figure out why I have death wobble above 45mph. Installed new MetalCloak adjustable control arms and trac bar on AEV 4.5” coil springs. New wheels are Hutchinson beadlocks with 5.28” of backspace. Based on videos I’ve seen from Dynatrac and on this forum it seems that this combination creates a very tight scrub radius. In my case it’s about 0.5”. The alignment shop is now telling me after my second alignment adjusting caster from 6 degrees to 7.5 degrees that I should only have a backspace of 3.5-4” My question is does or can having a smaller near zero scrub radius cause death wobble?


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Something has to be loose somewhere for death wobble to occur. Double check that all bolts are torqued properly and no parts have play.
 
JJ151 said:
Installed brand be Dynatrac XD60s a couple weeks ago and can’t seem to figure out why I have death wobble above 45mph. Installed new MetalCloak adjustable control arms and trac bar on AEV 4.5” coil springs. New wheels are Hutchinson beadlocks with 5.28” of backspace. Based on videos I’ve seen from Dynatrac and on this forum it seems that this combination creates a very tight scrub radius. In my case it’s about 0.5”. The alignment shop is now telling me after my second alignment adjusting caster from 6 degrees to 7.5 degrees that I should only have a backspace of 3.5-4” My question is does or can having a smaller near zero scrub radius cause death wobble?


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So the increased caster and told you to get wheels with less backspacing? Sounds to me like that shop really knows what they are doing. Maybe have them work on a Barbie hot wheels instead.


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JJ151 said:
Installed brand be Dynatrac XD60s a couple weeks ago and can’t seem to figure out why I have death wobble above 45mph. Installed new MetalCloak adjustable control arms and trac bar on AEV 4.5” coil springs. New wheels are Hutchinson beadlocks with 5.28” of backspace. Based on videos I’ve seen from Dynatrac and on this forum it seems that this combination creates a very tight scrub radius. In my case it’s about 0.5”. The alignment shop is now telling me after my second alignment adjusting caster from 6 degrees to 7.5 degrees that I should only have a backspace of 3.5-4” My question is does or can having a smaller near zero scrub radius cause death wobble?
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WTF? Ummm, I think you need to find yourself a new shop. MORE back spacing is what you want and near zero scrub radius is AWESOME and desired. Not only will it make turning easier and better, it'll also help protect things like your ball joints and help keep them and your wheel bearings from wearing out prematurely.

Death wobble is caused by loose or worn out steering and/or suspension components - PERIOD. If everything is new on your Jeep, you most likely have a bolt or two that isn't tightened to torque spec. If everything is, the quality of your components probably suck and they're allowing for too much movement in the bushings or are flexing. You should NOT need anything more than factory caster and that's 4°. If you have 6°, that should be awesome and no more is needed.
 
wayoflife said:
WTF? Ummm, I think you need to find yourself a new shop. MORE back spacing is what you want and near zero scrub radius is AWESOME and desired. Not only will it make turning easier and better, it'll also help protect things like your ball joints and help keep them and your wheel bearings from wearing out prematurely.

Death wobble is caused by loose or worn out steering and/or suspension components - PERIOD. If everything is new on your Jeep, you most likely have a bolt or two that isn't tightened to torque spec. If everything is, the quality of your components probably suck and they're allowing for too much movement in the bushings or are flexing. You should NOT need anything more than factory caster and that's 4°. If you have 6°, that should be awesome and no more is needed.
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That’s what I thought. Dynatrac says 6 degrees too.


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Here are 4 pics of the front upper control arms. The first 2 are the passenger and the second two are the drivers side. Both sets are on the axle. It looks like there arm sleeve isn’t seated properly? I’m not a mechanic so am not sure. For those of you that do installs, what’s your opinion?

IMG_2610.JPGIMG_2612.JPGIMG_2613.JPGIMG_2614.JPG


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JJ151 said:
Here are 4 pics of the front upper control arms. The first 2 are the passenger and the second two are the drivers side. Both sets are on the axle. It looks like there arm sleeve isn’t seated properly? I’m not a mechanic so am not sure. For those of you that do installs, what’s your opinion?

View attachment 324591View attachment 324592View attachment 324593View attachment 324594


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That bushing that looks like it isn't pressed in all the way in, actually it is. OEM or aftermarket, that is ok; that's how it is.

Check to ensure ball joint nuts are tight and track bar bolts are torqued properly to 125 foot pounds. Check drag link and tie rod nuts also. And of course ensure your lug nuts are tight.
 
Just to make you feel better, here's an OEM axle and a prorock showing that same bushing.

IMG_20190407_144404_167.jpg

IMG_20190407_144436_953.jpg
 
WJCO said:
Just to make you feel better, here's an OEM axle and a prorock showing that same bushing.

View attachment 324600

View attachment 324601
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Thanks for the feed back. While I’m glad it’s correct i still can’t figure this death wobble out. Checked the torque on all the front arms and track bar. Will recheck tie rod tomorrow. Torqued the wheels and even swapped front to rear (had them balanced twice with no changes). The saga continues.


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WJCO said:
That bushing that looks like it isn't pressed in all the way in, actually it is. OEM or aftermarket, that is ok; that's how it is.

Check to ensure ball joint nuts are tight and track bar bolts are torqued properly to 125 foot pounds. Check drag link and tie rod nuts also. And of course ensure your lug nuts are tight.
Click to expand...

Should all the suspension components be torqued to 125 foot pounds or are there different amounts depending on the component? What is a reliable source for these torque specs?


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After you have checked the front track bar, check the usual causes of death wobble: play in the ball joints and wheel bearings. Don’t assume that they are fine because they are new or near new.


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fiend said:
After you have checked the front track bar, check the usual causes of death wobble: play in the ball joints and wheel bearings. Don’t assume that they are fine because they are new or near new.


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I will have the shop check these out tomorrow but I guess I would be very surprised that Dynatrac would have not caught this in QC before sending out. In my email correspondence with Cory at Dynatrac he has not referenced checking their work once and says it has to be something else. He very well may be right but at this point when you’ve checked everything else you’re left with checking the not so obvious or expected. Thanks for the direction!!


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So I found that the front upper shock bolts needed to be tightened. We’ll see if this fixes the problem. At this point I’m still going to rent a U-Haul trailer to get my Jeep to Moab. Too uncertain about death wobble to flat tow?


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Can you post a picture of front axle which shows tie rod end to end and steering linkage? I want to see drag link/track bar angles etc.


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Tough to see with splash shield and stabilizer in the way but it doesn’t look like they are parallel. Tie rod looks like it is bent weird too. Try having someone saw the steering wheel back and forth sharply and look for movement in joints and track bar bushings.


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