Iant333

My Jeep has been grinding/vibrating for like the past month and a half now, it still drives "ok" and i have put prolly 2000 miles on it like this but it is driving me crazy. I have tried just about everything I can think of and I still cant find the problem. For the record I am running a stock 2001 slip yoke/driveshaft on about 3.5 inches of lift, NP231 t-case and an Aussie locked 8.25.


Problem:
If you are on the gas any significant amount over ~55 it vibrates really bad, like it feels like you have a massaging seat. If you are coasting at any speed over ~30 it doesn't vibrate but it makes a somewhat loud clinking/grinding sound. If anyone has heard a really bad driveshaft slip-joint it sounds exactly like that.

This started right after I did my gears, however I'm pretty sure it isn't directly related, there is no sign of abnormal wear on the gears or my aussie locker and I have changed the fluid twice since the break in period and there is no excessive metal shavings or anything out of the ordinary in there.

At the same time as the gears however I also messed around with the leaf pack giving it an additional inch perhaps of lift in the rear and removed the shims that were in there. The removal of the shims brought the pinion down from pointing well over the angle it needed to be (pointing way too high since lift shackle install) to pointing directly at the T-case. At first I thought it was the incorrect pinion angle causing this so I threw a 2 degree shim in there. It made the angle much better, it is still maybe ~2 degrees too shallow but it made absolutely zero difference with regard to the problem.

I changed the t-case fluid this morning, no metal shavings or anything out of the ordinary. The case also shifts fine and behaves normally in 4wd. The rear output yoke has absolutely zero play, the front has maybe a 16th of a turn which is supposedly normal, the rear axle yoke has about this much as well but it is normal with a locker.

The front driveshaft was totally rebuilt about 6 monthes ago, I even did the centering ball. The front slip joint doesn't have any play.

I jacked the rear end up and ran it at about 55, it sounds like the sound is coming from the t-case or the driveshaft, pretty sure it isnt higher or lower on the driveline. While driving it sounds and feels like it is coming from right under the passenger seat.

So Basically

Stuff i've checked:

U-joint's
Axle gears
Stretched t-case chain
nothing obviously wrong with the t-case
anything dumb like loose u-bolts
Pinion angle (pretty sure)
Front driveshaft


Anyone have any more ideas short of throwing parts at it or taking the t-case completely apart to check for some funky *** internal problem? I cant think of anything more to even look at. Gonna talk to my driveline teacher at school tomorrow too and see if he has any input.

RoyalXJ

time for a sye

athenscj5

Yeah, SYE is what it sounds like you need. Mine does the same thing on a 3.5" RE lift that netted about 4.5-5". Over 30 mph when I let off of the gas, I hear and feel a grinding that I am pretty sure is the Slip yoke.

Dwinthrup

try dropping your tranfer case an inch I have a 4.5 lift and had to do a 1.5 drop problem was gone after that.

Vincenza V

If it is the SYE you need, don't forget about shimming the rear axle with quality wedges. I though JUST having the SYE was enough, wrong....