So this happened yesterday.
It became clear that I was getting unacceptable driveline vibrations after the lift. I was getting a throbbing hum from the back of the Jeep from 25 to 35 mph and again from 50 to 70 mph. The hum got louder with more throttle, quieter with less throttle, and didn't change when I changed gears, but did change with speed.
To me, that looks like the symptoms of a misaligned pinion. I did measure driveline angles before and after the lift, and I had good u-joint cancellation before the lift, poor cancellation after the lift.
I figure there are a couple of ways to deal with this:
* Drop the transfer case and possibly add a MML to reduce the driveshaft angle and move the pinion angle in the right direction.
* Get adjustable rear control arms and rotate the rear axle by about 4 degrees to get good u-joint cancellation.
* Get a SYE, DC driveshaft, adjustable rear control arms, and a rear track bar relocation bracket and redo the whole rear driveline.
I'm supposed to be leading a trail run today, so I ran out to a local parts shop and picked up the Rubicon Express TC lowering kit.
I did a test drive after the install and reproduced the same conditions and didn't get any noticeable vibration. If anything, there's maybe a tiny vibration at just over 70, but I may have imagined that, and I don't drive 70 anyway.
Hopefully the RE kit is doing the job, but I have to say I'm not impressed with it. The plastic spacers start getting crushed before you reach the torque spec on the bolts. And the washers deform before you get the bolts to torque. I replace the washers with better hardware, but the spacers are what they are.
Not recommended, but it will do as a temporary solution.
Next up is to look at adjustable control arms to see adjusting pinion angle lets me get rid of the TC drop.