Mystery Death Wobble In JK Unlimited
Q In March 2009 I purchased my first Jeep, an '09 JK Wrangler X Unlimited. In April I had a Zone Off-Road 3-inch suspension lift installed. I put on Pro Comp 17x9 Knight Khrome wheels with 35x12.50/17 Pro Comp Xtreme M/Ts. I also had a JKS adjustable track bar installed shortly afterward. Everything has been great until I put my factory tires and wheels back on for the harsh Ohio winter (a lot of road salt and brine water also). The factory tires are Goodyear Wrangler SR-As, 255/75R17s on the factory wheels.
I am having a problem with a "death wobble" at freeway speeds (65 to 70 mph) when I go over a bump on the freeway. The installation shop and I have both called Zone and BDS about this. They recommended that we install two-degree caster cam plates on the lower control arms. After the install, the death wobble was present at lower speeds of 30 to 40 mph. I drove back to the off-road shop and we adjusted the toe. The wobble is still present, and we are going to adjust the toe some more and balance the tires to see if they're out of balance. We have made sure everything under the front end is tight and to torque specifications.
I have not been off road with the Jeep yet, so it's mainly on the street, and is my daily driver. This is driving me nuts and is very frustrating. Is this common when switching back to the factory tires and wheels? Am I going to have to re-align the vehicle every time I change my tires for the seasons? Any suggestions, input, or ideas?
Cuyahoga Falls, OH
A It's kind of strange that the death wobble took place after you put the old factory stock tires back on and did not happen with the larger tires. If I read your email correctly, you made no other changes to the Jeep besides changing tires. Once the alignment has been set, it should not need to be changed. Some shops like to run a bit more toe-in with larger tires, as the tire seems to have a bit more leverage and push outward. But then again, toe should not have any bearing on the death wobble situation. Usually, improper toe-in causes the vehicle to wander, not wobble.
I would think that you would need about five degrees of caster angle. You said that you added two additional degrees of caster, but not what total caster was set at. Yes, lack of proper caster can help promote death wobble, but I would think that it would also be present with the 35-inch tires.
My first thought is that the stock tires are badly out of balance. Could you have run the tires at a very low pressure and spun them slightly on the rims? Could it be that somehow you used an air system that had a considerable amount of moisture in it and it was transferred to the tires? A chunk of ice would greatly affect the tire's balance and cause the wobble. Are the factory wheels sitting true on the hub with no interference from spacers of any kind?
If these things all check out, I would suggest going back to a hands-on approach to all the suspension components. Pull, tug, and pry on every mounting location, every tie-rod end and bushing, and search for movement. Jack a wheel off the ground and grab it at the top, and check for any in-and-out movement such as would come from the wheel bearings. Then grab the front of the tire and try moving it in and out. Have a helper watch for movement. Sometimes the smallest amount of wear can cause a death wobble.
Finally, when the Jeep was on the alignment rack, did they check for proper axle camber? When used very hard, it's not uncommon for JKs to bend a front axlehousing; however, this shouldn't cause a death wobble.