yesterday I was pulling a dump trailer around the yard with 7 yards of top soil and got stuck in some very light mud ( rained the night before and ground was a bit soft). my tires are beat and don't have much tread left, so it wasn't a surprise that I got stuck with 10,000 lbs behind me in slippery grass/ mud.

I had switched my '89 F350 into 4wd low (bw1356 manual t-case and manual hubs) long before I got stuck (creeping through the yard is easier). Everything was working for a few minutes after i got stuck while I was slipping around (board here, dig a little there) with both sets of wheels spinning a bit. at one point I rocked the steering back and forth hoping to catch a groove when the front wheels just stopped. I didn't hear any noticeable pops or booms (need to replace my right universal and bearing though and was hearing an occasional pop before getting stuck).

Any how, I unhitched the trailer and got the truck unstuck but 4wd won't engage now (definitely not in low, hard to tell for sure in high- wet and slippery, remember). lights come on on the dash (heigh and low), and I hear the t-case switching & it feels pretty smooth. I locked and unlocked the manual hubs a few times with no luck (both felt fine). put t-case in 2wd and spun the front axel- turned well with both yokes spinning in opposite directions (again the font right had some resistance and wasn't playing along as well as the drivers side). put her in 4wd (i think i only tried high) and turned the axel again and it locked in with a confident 'click' and then obviously stopped since I'm not quiet strong enough to turn the entire drive train and crank the engine by hand.

okay, a few questions-
1) is the Dana60 limited slip, and if so what's it like when ls goes out?
2) is it possible that I blew something in the bw for 4wd low only. if so, what?
3) I'm going to test it again to make sure the 4wd low engages as well, but what else should I check?
4) could both of the hubs died at the same time (old original Ford hubs)? if so would the axle have stopped when I put tested it in 4wd?

 

I would look at your locking hubs

 

It's possible the T-case just slipped out of gear, if your shift linkage is stiff and hard to move(very common) it may not have been in the exact right position to begin with, dismantle and lube that sucker up if this is the case. The hubs are always a possibility as well, may have partially stripped one due to worn or seized outer drive axle u-joints so now it still engages but lets go under load.