Ok, I've been after this issue for a while and I'm stumped.

98 4.0 AX15 4wd
3" lift, 31" tires, hack/tap SYE, pinion shimmed 4° up

This thing shakes... VIOLENTLY when I take off from a full stop.
If I pull the parking brake and slip the clutch as if I'm going to take off, it doesn't shake. That should tell me the clutch/pressure plate isn't the issue. Clutch is about 2 years, 24k miles old.

Things I have replaced:
-Rebuilt both driveshafts
-New motor and transmission mounts
-Rear leaf spring bushings
-New (stock) shackles
-leaf spring clamps (2 of them were broken)

Things I have checked:
-Hack & Tap was my #1 suspect, but it is TIGHT. And it never gave me any problem for the first 18 months, I don't see why it would start now.
-transfer case bearings. Slight in/out play, no up/down. I have 3 NP231s and all 3 of them have the exact same amount of in/out, and no up/down.
-Exhaust hangers (for giggles)
-Leaf springs are not cracked anywhere
-Rear pinion play. There is none.
-Bolt torque. I have checked, double checked, and triple checked damn near every bolt I could think of. Motor mounts, mounting brackets to the engine, mounting brackets to unibody, leaf spring bolts, transmission bolts, bellhousing bolts, tcase to trans bolts, driveshaft bolts... etc.

It only seems to shake like that once it's warmed up fully. It only shakes from like 0-1 MPH. Even if I sloooooowllllly engage the clutch, it still shakes. The shake DEFINITELY feels like it's coming from the back. No bearing noises while driving. The rear end sounds good and quiet. Matter of fact, I recently drove from my house in SC to Key West and back without issue except for the takeoff shakes. It does seem worse with heat soak and load. If I have the family along it seems worse.

I'm just out of ideas now.

 

Do you have a lunch box locker in the rear?

 

Nope. There's one in the front though.

I'm pulling the rear diff cover tomorrow to have a look. I really don't think there's anything odd going on on there, but I feel like I'm out of things to check except that.

 

Mine had a terrible shake when letting the clutch out and for whatever reason ended up being the rear locker. Everything was new, gears, carrier, bearings, locker.... Put the oem spider gears back in and it was like a new Jeep again.

Have you popped out the rear shaft and see if it still does it in 4wd? That would at least eliminate or pin point it to something in the rear end.

 

I tried. You know how hard it is to drive on the street like that? Locked and FWD is terrifying.

 

Wait, you mean you like being able to turn? Where is the fun in that?

 

It's not even the turning part. There aren't any spider gears. On takeoff, it just grabs one wheel with all the torque and rips it out of your hand. Then after it does that for a bit, the locker has enough relative motion to finally lock up. Since you're already holding the wheel to one side for dear life, it rips you the other way.

Wouldn't be so bad on a dirt road, but this is dry pavement with other cars around. Plus, I'm focusing on that so much that I forgot the task at hand.

So yeah, that test was inconclusive. I couldn't really even get things heated up enough to tell a difference.

I will say that it shakes in 2H, and selecting 4H makes no difference.

 

By removing either the front, or rear driveshaft, you can narrow it down to the front or back causing the issue.
Especially if its happening at low speeds.
If removing either one doesn't clue you into the problem, it's a lock up issue with the tcase and your SLE.
Those angles that they put the driveshafts at are extremely well engineered. When we alter them... you get the picture.





Good Luck, and God Bless.

 

Any Resolution to the jerking around?

 

I ended up replacing the clutch yesterday. I drove around town for a couple hours after and haven't had a chatter since.

I was nervous when I saw the one I pulled out. It looked like it had maybe 1000 miles on it, if that. The disc was in great shape, had plenty of life left, and the pressure plate looked almost perfect.

The new clutch went in and it's been buttery smooth all day.

 

This may be way off base, but in my old VW, that i still have, I had the same symptoms. Replaced the clutch and all was good for a while, then they came back, Pull the motor to put in a new clutch and I see 'blueing' on the flywheel, in about 3 spots. Very distinct. I showed that to a VW expert, and he said the flywheel is warped, and a new clutch will work for a while but wont last long. A new flywheel solved the problems, and it hasnt came back.