As I told everyone in the past I joined the heard and got a sheep.1999 xj cherokee with the 4.0. Well I just finished up installing a rustys 4.5" lift on it and now I have a concern.I am hearing from some guys that I should install a slip yoke eliminator and others say I dont need it.Well they are $200 bucks plus like300 more for installing it.Do I really need this item??? If I dont install it what parts would the damage if any occur to.By the way the lift kit came with a transfer case drop so the angle shouldnt have changed to much.Thank's for any tips opinions in advance.And keep in mind Im from michigan so there is no rock crawling involved ever just sand dunes and mud...

P.S. sorry its been so long since I've posted but I have been out of town for quite awhile...

If you're not getting driveline vibration, you're probably OK. Jack it up at full droop and see how much slip yoke spline is still in contact in the case. If it's less than an inch and a half, I'd do something.

and dont forget to overfill the diff because I believe your pumpkin is at an angle now.

You only need the SYE if u want more ground clearence and stuff the driveline back into teh frame where it belongs. Then you need the SYE, and a CV shaft, and change your rear pinion angle accordingly. A good reson to have one beyond that, is for trail repair. Break a rear shaft/u-joint w/out SYE, and you're SOL Leaking ATF all over the ground from an unplugged slip yoke is bad! W/the SYE, just remove busted rear shaft, and drive home on the front driveshaft!

On a '99 you should get the SYE. The yoke will wobble, even if you don't feel it, and destroy the output bearing in t-case. Early models could get away with 4-5 inches but they changed the output on later models, '97 up I think.
Did you get new rear leaf packs or add-a-leaf and shackle? With new springs, your pinion angle will be okay, but longer shackles will change the angle and cause vibration.
On my '88, I was able to use a longer driveshaft vice the SYE, this was to be temporary until I could get the SYE, but something happened to the Jeep before I could finish it.

Its the add a leaf kit with shackles.I cant really feel any vibration except at one spot between 50 and 55.But I also know the tires are out of balance a little bit to.I called the guys from rustys and they said definetly use the slip yoke eliminator but I'm not sure if there just trying to sell me stuff or not...I appreciate the help and keep the opinions coming please I am setting this truck up for our honeymoon being spent at silver lake sand dunes and I need it to be right.Everyone knows if your g/f or wife isnt happy she can make it real unhappy for you especially on your honeymoon...

If I may make a suggestion, try here.

Thanks for the tip I'm going to go get new tires tomorrow and see how it goes from there to see if I still have a vibration or not but I think I should definetly go for the sye...

You would install a slip yoke eliminator so you could get rid of the stock driveshaft and install a double cardan driveshaft in its place. The double cardan unit will handle the breakover of a lifted vehicle. You also have to reset the pinion angle on the rear differential. You use adjustable upper control arms on a TJ--don't know how its done on leaf spring sheeps. If your getting a vibe at 50-55--it's probably your driveline angle. You can either drop the transfer case, install a motor mount lift, or go with a SYE and new driveline as mentioned.

Angle Shims between the leaf pack and the axle will reset pinion angle on a leaf sprung vehicle.

Well here's my problem I am totally new to the sheep thing.When I ordered my lift they told me I should go with a sye so I got it what they failed to tell me was I also needed a new driveshaft to go with it or at least I think I do???Once again I gotta say it this site just rocks I have to get a n4w sticker for the sheep just to show that not all sights are one brand and willing to help all...By the way 15 more days till the wedding.

Yes, you'd need a new DS with a slip joint built in.

great news I just had new tires put on and watched the guy balance them perfect and now I have no vibration at all.I mean there is a ride difference because of the lift but no more shaking...