Topic: 4wd didn't engage last night..heard a "clunk"...then it worked..then it didn't..

[Loke Groundrunner]

My '99 5-speed TJ (and I) haven't been offroad in a good while (thus haven't had a need to throw the old girl into 4wd). I got caught on a very "iffy" (and narrow) straight two lane road last night in a bad thunderstorm. Debris on the road...mud...potholes...and alot of water. I was only going about 30 mph and visibility was pretty crappy. I was starting to "wander" on the road (a bit) so I hiked her into 4H "just to be safe" as I was passing some oncoming traffic. The 4wd dash light DID NOT come on. I put the lever down again and pulled back up. Again...no light. I drove another 50 to 60 yards then heard a loud "thump". I though I'd run over something. I put the 4wd lever back down and kept driving. In a few minutes I pulled it up again and this time the 4wd dash light came on and everything was good till I got to better ground. Then I disengaged the lever. On the return trip (later) the SAME thing happened. No dash light and a pronunced (and delayed) "thump". Later the Jeep shifted into 4wd HIGH just fine. That "thump" has me worried. Never happened before. There was NO "grinding" sound of any kind. Just a delayed "thump/clunk". I must admit that I DO NOT push my Jeep very hard...thus the malfunction was pretty suprising. Does it sound like a transfer case linkage problem? It kinda seems like the 4wd might have been "partially" engaged and then slipped out. AGAIN...there was NO grinding ...just the "clunk" (and the unlit dashboard light). In 2wd it drove fine. Any tips appreciated. Hopefully I can have a look underneath tommorrow. Cheers.

[Jeffy]

Could you feel the wheel push and pull when it was in 4WD with the light off?  If you could then it was in 4WD but the light didn't come on.  The TJ's from axle is always locked,  all you're doing is setting the transfer case so it powers the front drive shaft.  4HI is synchronized and can be shifted while moving.  4LO is not so you will need to stop or almost stopped as it will clunk when it drops into gear.

[sharpxmen]

mine did that (delay light coming on and clunk) after not using the 4wd for a long time - but i have the disconnect passenger axle which you shouldn't, so when you actually shift in 4wd-hi should be engaged already as opposed to my '95 YJ where the axle disconnect is actuated by vacuum and the light comes on when the lever that moves the collar is in place. so to be honest i have no idea why the delay in your case.

[Loke Groundrunner]

I can't say that I felt it (like I would under normal circumstances.....and you are right...normally I can feel a little bit of a "tug"). Then again...the weather was bad and the road was rough. When I shifted I remember thinking "Did that work?". Then came the "thump" a few seconds later. Hmmmmm.

[YJmechanic]

tj have a pretty known issue with the shift linkage because of the design,  any change in can make the linkage not quite line up right and then shifting in and out can be a pain,  i installed a few conversion kit and that seems to help.  i think you were not completely engaged at first and then it dropped in,  check out your linkage adjustment and try it again.  may just not be moving freely since its been a while too