there are 2 reasons either linkage come adrift inside or shafts sticking in front output housing ,behind tin cover is usual place there are 3 shafts 1 with red knob on which selects high/low gears outer behind tin cover which operates 4wd dog and center with yellow knob acts as pivot for red lever to operate outer lever ,either jammed or pivot dislocated latter means box out ,to remove front output housing