Hey all, today we have a mystery that has stumped me and figured id ask here to get more ideas before i get under there again this weekend

96 XJ, 4.0 automatic, no leaking transmission, no leaking transfer case, no leaking oil.

Vibrations/Grinding around 1500-2200 RPM and doesnt want to shift SOMETIMES. Some times it works like normal, sometimes it grinds and grinds until i want to skip the gear and it goes right up to 3000 rpmish. Sound and feels like its right under my feet when driving and can feel the vibration/grinding.

When I get underneath, the front drive shaft has some play (can twist it maybe from 12 oclock to 1oclock easily, cannot push in and out), rear drive shaft is perfectly tight. Im hoping to get under there this weekend if its not raining and checking the U-Joints, tightening them, and that fixes it, i really hope its not the transmission itself. Any ideas are greatly appreciated, any questions and ill try to answer them quickly.
have not changed spark plugs yet

186k miles

 

Remove the front driveshaft and take it for a drive. Sounds a bit like the transfer case chain has given out. It also sounds like a lot of play for the front axle, but I'm leaning more towards transfer case right now.

 

assuming i dont go into 4wd would that cause any unintended consequences? New to the platform and not trying to be stranded by accident. Ill try this this weekend thanks.

 

Nope. Absolutely zero. Well, except that you won't have 4wd capability, but that's all. It's 4 bolts at each flange. All of them are 8mm. They round off easily too, so you'd be best off with a 6 point wrench.

I just went through this with my brother's Wrangler. He drove it for 3 weeks without a front driveshaft until I rebuilt his transfer case.

 

took it off and went for a drive, noise has stopped and shifts great.

The drive shaft compressed easily and a bunch of grease came out of a pinhole by the ujoint that is towards to the front of the jeep. Can still turn the transmission ujoint about from 12oclock to 1oclock.

so this tells me its probably the transfer case if it isnt the transmission ujoint nut needing to be tightened. Let me know whats up, thanks again so much

edit: drove it some more and it started to make the noise again, but this time a lot less frequent. So instead of the noise happening 70% of the time now it's only 10% of the time

 

Tightening the front output yoke won't tighten up that slack. That's the drive chain you're feeling. Luckily, rebuilding a transfer case isn't terribly hard. There are plenty of videos on the process. Or get one from a junkyard. Either way, check the fluid level for the time being. You might be able to eek a little more time out of it by topping the fluid off. (Even if you don't see leaks it could be low)

 

damn i was hoping i wouldnt have to take apart the transfer case, oh well. ill pick up a drive chain from rockauto and make plans next weekend to rip her out and do some wrenching.
luckily no leaks and I checked the fluid on thursday and shes topped off. Still think its weird the grinding/vibration feels like its under my feet while driving instead of the transfer case since its by the middle/rear axle. Nature of the beast! thanks for the assistance brother

 

Check the front axle before ripping the transfer case out. Maybe get a tube of RTV and a few qts of gear oil and pull the front differential cover. It's hard to diagnose things without me being there and seeing it, but it sounds like we're on the right track at least. Is there any up/down play in the pinion yoke on the front axle? If you do pull the cover, look for glittery fluid.

 

no play on the axle yokes, and i unscrewed the diff plug and stuck my pinky in, yellowish clear with no glitter just some dirt and grease on the gears inside. Gonna do some looking researching more on similar issues others had

edit: to add it was pretty low on gear oil, like a good 1.5" below the fill hole. Deciding if i want to top it off for a week, then take it off and inspect it next weekend