Issue Revisit...Any bigger tire than stock = 40 mph shake

Hey all,

Ok if you want to do some reading on the history of this problem, check this out: http://www.naxja.org/forum/showthread.php?t=88504&highlight=green50gt

This was a while back when i was running TSL SX's. Nevermind most of it, as all that suspension is gone, as are the tires. Same problem though.

For about the next month Im running a 4.5" RE lift. Rusty's control arms, RE springs and shocks, and RE 1600 Track Bar. The Jeep has been aligned several times.

The issue is if I put a bigger tire both in dimension and weight, I have a shake or wobble at about 40-50 mph. For the last couple months I have been rolling around on Rubicon wheels and tires, everything was great, no shake/wobble at all. last night I off'ed those in favor of some 33" Trxus and Eagle Alloy 186's, both of which were brand new, and the shake/wobble is back. This is the 5th set of wheel and tires that I have ran. All the suspension is new, and its been aligned multiple times as previously stated.

I dont understand...Could it be like a ball joint, or maybe I need a real heavy duty steering stabilizer? Maybe a 2nd steering stabilizer? If it were a bent axle wouldnt it do it no matter what type of wheel and tire combo i use?

It's nearly at a point where this is irrelivant, as this is now going to be a trail rig only, but there will be times where i will have to drive it to the trail, go to Jeep drive ins and whatnot, and it would just be nice to get it figured out so if i did have to drive it on the street it would be street friendly. My Rock Krawler 3 link should be here within the next few days and im swapping to 5.5" coils and a 1" spacer, HD RE track bar and mount.

Unfortunately, by design, the XJ/MJ hides its death wobble flaws easily. There are MANY things that could be going on. Ive seen small frame cracks under the steering box, the aluminum isolater allowing the box to back off a bit, or crack, and the whole track bar deal is crap, the track bar could be worn at tie tod end, bracket be loose, or even frame cracks under the bracket allowing some flex. The oddest one Ive ever dealt with was a faulty unit bearing assembly, that you couldnt move AT ALL statically, but after replacement of them (had to do both, couldnt tell if it was neccessary, so....), no more death wobble. FInally, ball joints can be a tricky diagnosis as well, thy can be worn and allow the dreaded death wobble.

I chased a vibration similar to what you are describing for a long time. Unfortunatley, there doesn't seem to be a definative answer for it. I had two sets of rims, and three sets of tires and they all did the same thing. I upgraded to the same track bar you have, and added a new stablizer. I finally changed my ball joints and front u-joints this summer and that helped quite a bit. It's still not perfect, but a lot better than it was. If you haven't done those, it might be the next step.

The other thing I thought of, how are your hub assemblies?

The track bar is brand new, so I am assuming that isn't the culprit, plus it did it with the stock one too.

To be honest I'm not sure how to check the hub assemblies, aside from just replacing them.

Whats funny is if you look out the window at the time of the shake/wobble you can see the tires shaking back and forth, and you also REALLY notice it in the steering wheel. But it's only between about 40 and 50, if you go faster or slower its perfectly fine.

If you can see it wobble, obviously something is loose. The way you describe it sounds like a tire balance issue (or out of round or something), but you having checked all that, I'm stumped.

How many miles on your stuff? Like I said before, my guess would be ball joints or hubs now.

My Jeep has 71,000 miles on it. Something is very wrong. I guess I'll take it into a really good alignment place and see if they can figure something out. I might just leave it alone until I get the long arms on and new springs. I took it down to the corner about a mile to the gas station, its bad. Right at 40 it starts doing it, almost as if someone flipped a switch.

HOW MUCH NEGATIVE CASTER ARE YOU RUNNING IN THE FRONT AXLE? Had the same issue with an old Scout I built years ago & I put 4 deg neg caster in the front & the problem went a way....

I have absolutely no idea. It has stock upper arms and Rusty's Lower arms.

The most common cause of Death Wobble is too much caster and not
enough toe. With a lifted XJ setting the alignment to factory Spec’s
can cause this just buy hitting the smallest of bumps. The second most
common cause is a gear box that is out of adjustment. Witch is what sounds
like the problem with your XJ. I would recommend setting the Caster to
around 4 degrees and set the toe to 1/8” in. and adjust up your gear box
about a ¼ to ½ a turn. When changing wheel and tire combinations
this can change toe settings because the center line of the tire is different.
Widening out the track width with a different offset wheel also changes
toe settings. I would recommend an alignment from a reputable shop
to these spec’s and the tires you plain on running.

David Rizor said:

The second most
common cause is a gear box that is out of adjustment. Witch is what sounds
like the problem with your XJ. and adjust up your gear box about a ¼ to ½ a turn.

Click to expand...

Can you explain this more?

Go to your local Harborfreight Tool or Hardware store & buy a cheep angle finder & place it on top of the knuckle where there is flat area, that will tell the deg of caster you have. It MUST me NEGATIVE or rearward tiping, Caster is huge on a lifted truck & is a amust have, I have found this to be the issue on most lifted street driven trucks. Put Negative caster in & I will bet you 12 pack your problem goes away..... Only thing you will loose is a little angle on the front driveshaft u-joint =)