Not sure exactly where my problem is. I just got this truck a few weeks ago, 1994 f250 7.3L manual, automatic locking hubs.
Truck works perfect in 2wd. When I put it in 4wd and start driving there is a loud bang and what feels like a gear slip. This continues loudly and repeatedly if I leave it in 4wd driving slowly up my dirt/gravel road. I pulled the hubs, cleaned and packed them, they look and operate fine from what I can tell. On the passenger side, the splined washer behind the hub and snap ring was worn and had obvious cut and scratches in it. After searching all over I finally found one, replaced it but the same problem remains.
Any ideas one what this might be? Thanks.

 

Did you test-drive it in 4WD before buying it? My first guesses would be the t-case & front diff.

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Yeah, I test drove it. The 4wd worked great for a while but I have a 2 mile rough 'road' that I drive twice a day that has a knack for exposing problems in vehicles.

 

Well, in case any one else is having this problem, I fixed it. There are two large lock nuts behind the hub with a fixed washer between them. The first one you see as you pull them out should be 160-200 ftlbs tight, mine was finger tight. I also put in some manual Mile Marker hubs. 4WD works perfect now.