Vibration after <2" lift, U-Joints? SYE? T-case drop?

I just put a roughly 2" lift on my '99 Cherokee Sport, using 4886186AA springs in the rear, and Moog CC782 coils + 3/4" spacers in the front.

Unfortunately, I now have massive vibrations ~35mph and up. I guess late XJs can have vibrations at low lifts, and I'm just unlucky.

1. My mechanic friend suggests changing the U-joints out, on the theory that even though they feel tight, they might have been pushed over the edge by the added lift.

2. I've seen references that the late XJ Upcountry Models had a TSB or similar to put in a mild t-case drop due to vibes. I'm a little tempted to try adding 1/2" of spacers and see if that helps.

3. I'm not really opposed to doing a hack and tap SYE, but I see references for using a front drive shaft with them at 3+ inches of lift, so I'm worried that with my tiny lift the shaft will be too long.

I am NOT likely to lift this any more, I just wanted a little boost, and to run 30" tires. Thanks for any help!

check the double cardan joint on your front shaft. any play in it all, need a yoke centering bearing. they're usually shot by the time they're teenagers, yours will be 20 next year.

try to avoid TC drop if you can. shouldn't be necessary with 2" lift anyway

You are right, the 99s don't like lifts. But 2" should be OK. The vibes come from the slip yoke being pulled out too far. Could you take a pic of your output shaft and yoke so we can see how far out it is?

Attachment 14459

That's what the output shaft looks like. I'm also wondering if I have more lift than I think I do. My stock springs were shot, so it looks WAY higher, but maybe its over 2" in the back?

That doesn't look like it might be out too far, but grab that yoke and wiggle it up and down. If it does wiggle, then it is out too far. Also, visually inspect the pinion angle and compare it to the output shaft angle. You can get a free app for a smart phone to help with this. It needs to be within 4° or it will vibrate

I didn't notice any wiggle last night, but I'll check it again after work and try to measure angles.

Any chance the marginal u-joit theory might be true and they're just acting up now since they're at a different/bigger angle. They may well be stock at 165k
, since the previous owner (good friend of mine that bought it at ~40k doesn't remember changing them).

Always a possibility

they look original

I just bought a set of spicer replacements for the two rear u-joints from Amazon for ~$40, I'll have them Friday and try to get them on this weekend. That seems like a next logical step to take.

Is there a way to measure to see how much lift I actually got out of the Crown HD rear springs? I.E. center of the wheel hub the fender?

Yes there is. Measure from the center of the hub to the fender flare and subtract 17" in front and 17.5" in rear. If you have trimmed the fenders, measure to the crease above and subtract 22" front and 22.5" rear

20" front, 20.5" rear. I think I got way more lift than advertised out of the Crown HD "Up Country equivalent" springs. Hack and tap time?

Probably so. Better bite the bullet. Get it installed properly and you will be glad you did

the bright side is, you got much more lift and can run more tire!

Sadly, I already bought 30x9.5 Falken ATs for it, probably could have went with 31's, abet with rubbing on turns. Oh well. Are there any other modifications I need to do at a ~3" lift that I ignored since I thought I only had 2"? I did get longer (and I think long enough shocks).

Do I have to mess with axle shims too, or can I just do the Iron Rock hack and tap, throw in a front shaft and be good?

On another note, the local junkyard things they have a front drive shaft, but its already pulled, and just labeled "jeep". Does anyone know the collapsed/extended lengths on a XJ, Automatic, 89-01 front shaft? I can measure mine, but its at home and the Junkyard would be easy to stop by on my way home tonight.

Also, as another thought, 30" tires might not be too bad if the springs sag back down to the advertised ~2" over time.

I had a thread on this here, but thanks to Photobucket, you cannot see the pics now. Basically with a double cardan driveline, the pinion angle should be the same as that of the driveline. In other words, when properly aligned, the U joint should not have any bend in it