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Discussion Starter · #1 ·
2013 Jeep Wrangler UR 6-speed 80K miles AEV 4.5 lift and 37x12.5 BFG KO2

Got a weird one here. I have some vibration at highway speed under load. Accelerating or lugging up a hill. Once I am on level or down hill it goes away.

I thought it was maybe the rear driveshaft but that all looks perfect and no play. You can feel the vibration in the seat of your pants and it actually feels like it's binding slightly causing a power lose.

Any ideas? I take pretty good care of it and regularly change diff, transfer case, and tranny oil as well.
 

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Discussion Starter · #3 ·
I got some time off and removed the front drive shaft. I still have the vibration. I discovered that I have 3/8th inch of rear axle drag when I had my wheel alignment checked. It could be that the drag is causing abnormal tire wear so I just bought a pair of Synergy adjustable rear control arms so I can correct it.
 

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I got some time off and removed the front drive shaft. I still have the vibration. I discovered that I have 3/8th inch of rear axle drag when I had my wheel alignment checked. It could be that the drag is causing abnormal tire wear so I just bought a pair of Synergy adjustable rear control arms so I can correct it.
Did they mean the rear axle was offset to one side by 3/8"? Or the rear axle is not perpendicular to the frame/parallel to the front axle? I've never heard the term XX inch of axle drag before in terms of alignment.

Do you have the factory rear drive shaft still or aftermarket? Vibrations can be really hard to track down on a lifted Jeep as sometimes it is just harmonics and nothing is "wrong". However, a lot of times a vibration under load at speed is due to the pinion angle of the rear axle being slightly too low. As the engine gets under a load, the torque tries to drive the pinion angle upward. This can compress bushings/etc enough to change the pinion angle a few degrees.
 

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Discussion Starter · #5 ·
Drag as in Thrust Angle. The real axle not parallel to the front axle. On a laser alignment machine the amount of thrust was .32 inches.

I installed Synergy Rear Lower Control Arms and we ended up extending the control arm on the rear drivers side to eliminate the thrust.

I have been driving around for about 2-weeks since the thrust has been corrected and all of the rumbling under load has been eliminated!

What really clued me into identifying the tires was the frequency of the rumble and that it would match up with the tread pattern.

Unfortunately the axle rotated enough during the adjustment that I now must by the rear upper control arms to get the pinion angle back where it should be. The upside is that these control arms adjust without disassembly and shouldn't come loose like the jam nut control arms tend to.
 

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Discussion Starter · #7 ·
The only reason I'm getting them is because of the thrust angle being off. I have over 87K on my rig with lots of wheeling and the rear driveshaft is still like new as expected. AEV knows what they are doing and OEM like reliability is a BIG part of what they do.
 
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