I recently bought an 83 cj7, and the D300 immediately developed a problem where I can't get anything from the rear wheels unless I am in 4L. Any recommendations before I tear the case out? I'm not sure what I should be looking for in the shift linkage itself.
Sounds like a linkage problem. The shift rail is not moving far enough to engage the rear output. Get underneath and have someone move the shifter between neutral and 2 high. See what can be done to move the shift rail that's moving farther than the shifter is currently moving it.
I am at times able to get the case into 2H or 4H, but it seems like it may be the whole motor/tranny/transfer case shifting position relative to the frame. The motor mounts look about shot. If I replace these and the tranny mount, is there anything special I need to about mounting and alignment?