I am having trouble finding a solution for my 92 XJ. When I switch into 4hi on my county road, the part time light stays on and I can feel the change in gears - BUT, anytime I am going up a large dirt/rock hill on my way home, i can hear gears slipping/popping from the front axle - like the wheels/axle are struggling to stay in 4WD when I need it most. I do not have a front axle vacuum actuator like the 84-91s and I have checked the front differential (no problems there). I have tried looking for 4WD vacuum problems for the 92 XJ - but haven't seen anything particular to my situation. My local mechanic does not believe it is the T-Case, but I am not willing to rule that out. I do have a 3.5 lift and a rebuilt Straight 6, but other than that my jeep is non-modified. Would the larger tires/wheels be causing this with the front differential gear box?

 

My first thought would be the t-case, sounds like the chain is slipping under load. try and drin the fluid in a white container and look for metal shavings. have you pulled the diff cover and checked the spider gears and the axle splines?

 

Larger tires should be no problem if mechanically things are normal, all
four tires are the same size, and the front and rear axle ratios are the same.

Here are some things to check or consider if you have not yet done so.

Did you open up the front differential to check it? Is the oil level full?
Any sign of leaks at the pinion? Any play at the pinion yoke?

Did you check the front axle wheel u-joints? They should have no play
in them. (IMHO this is the most likely source of the noise you are describing).

Are the front wheel hub unit/bearings both good?

 

Does it sound like this? If so probably t-case chain jumping the sprockets. You can crawl under there and twist the front drive shaft back and forth and listen for the chain slapping the case. If it needs a rebuild it's not a big deal they're super easy to overhaul, or you can go fish one out of a used Jeep for cheap.