Hello all, great site, thanks to all for their questions and all the answers
I just bought a 93 wrangler, 6 cyl, 5 speed worth 31 tires. I put in a 2.5 rough country lift. After the lift, it felt like it was binding and difficult to get up to speed in any gear. Called rough country (RC) they suggested lowering the transfer case 1/4 inch. I did and it helped and I had the front aligned. But, I still have a shimmy in the transmission when I start in 1st gear, a vibration in 2nd, 3rd, and 4th gears during accel and deceleration. If the clutch is pushed in or put into netural, the vibration disappears.
I had the same issue on my 95 YJ after installing the same lift. I'm guessing that you got closer to 3" of lift. If that happened you will need to install a slip Yolk Eliminator and new rear drive shaft. As soon as I did this the vibration stopped.
Go to Tom Woods home page and halfway down right side grey banner labeled Technical Information and Sponsors. Open that and start reading. It has more than you want to know about drive shafts and pinion angles.
Pay close attention to two pictures of the drive shady angles.
Without an SYE and double cardon joint shaft your pinion angle is level with the T-Case. With your lift kit I bet you had wedges on the rear springs which have you pinion angle up.
Get a magnetic angle finder at a hardware store and figure out what you have and then go from there.
Before you get the SYE check your drive shaft angles. Your transfer case yoke and rear pinion yoke angles should be the same. You can correct that with shims. (get steel ones not aluminum if you need them) Also double check to make sure your yokes on the driveshaft are timed correctly (in line with each other. not sure how else to describe that) That can cause vibrations as well.
I spoke with Eric at SBC today, he gave great advice and I made all the suggested checks. Then I lowered the t/c to a total of 1/2 inch and the yoke is back in the original position. Test drive was perfect. Thanks to all that posted.
Looks like SBC will be my vendor in the near future.