255,000 miles. New long block, rebuilt tranny. I've searched the forum and nothing really matches my symptoms, which are:
Engine runs great, nothing significant noticed in transmission which Shifts fine and has been rebuilt.
First symptom was the hi/low 4x4 handle slammed into my leg at 70 mph along with a significant Bucking two more times and immediately went away. It then did not happen again that first day. Sometimes now, it never happens. More often I feel it buck on occasion. happening more and more. Almost feels like I lost a tooth in a gear and it slips and then catches with the 4x4 selector slamming to one side.
Never had an issue like this, confused.
I can replace the transfer case etc, but would like the opinion of the group on likely problems. Did check rear pinion shaft for lose nut.
I'm thinking I'll start by dropping the drive shafts one at a time to eliminate the differentials, any advice on troubleshooting will be appreciated. Money is an issue for me.

 

Check for a broken transmission mount.

 

I just joined the forum in order to find a solution to the identical problem with my 1999 Jeep Cherokee Classic. I have >200,000 miles on the vehicle and it's performance, for all those miles, has been excellent. The bucking only happens when I am on the highway and is detectable only when I am accelerating or climbing a grade. I will be checking periodically to see what responses you get to your inquiry. Good luck to you in finding a solution as I am hoping to share in your luck.

 

Not the mounts, thanks for the help Dave 1123 - I think it's a planetary gear or the chain in the transfer case. The transfer case has all the 250K miles. My symptoms are exactly the same as yours Sawmill. Under acceleration, the more power applied, the more significant the bucking. I found a junk TC (249) for 200 and I'm going to change it next week. It's just a guess, but it's also a cheap solution to try. Since you have the same symptoms - Seems like this might be a common problem, but no real solutions from the group yet. Being Father's day weekend, I think the group is having BBQ and beer. Me too. I'll keep you up to speed on my troubleshooting.

 

Driving with overdrive has no impact, happens in both modes. Appears to be more significant when cold. Any help will be appreciated

 

Did you check on that spring? Sawmill, we've been private messaging and I told abqdave about the detent spring inside the t/case that keeps the shifter quadrant located in each gear. It's under a large hex plug on the bottom of the t/case. There is a spring and a plunger that rides on the quadrant under that plug. If that spring is broken, there's nothing to keep the shift fork from allowing the t/case to pop out of gear.

 

Dave 1123: Thanks, I'll check the spring. Not getting PM's for some reason.

 

Dave 1123 gave me some good tips. To add a symptom, when I held the Hi/Lo selector handle, I could feel it slip in and out of gear without the handle being moved, but the handle would try to back out of gear slightly, leading me to be very confident of Dave1123's diagnosis. It was the detent spring in the TC, making it a very easy repair. Just in time, the jeep will be in the woods in Southwest NM this weekend!! heurah!!, spelling intentional.