LT77 transfer box dismantling

I am intending to "go inside" my LT77 transfer box as I am having difficulty in selecting high box (I have checked linkage play and there is no fouling) The gear keeps spitting out under load and on overrun. Low box is fine. Box noise is not evident . The only thing I can think of is a bent selector.
Can anybody please advise.
Many thanks Ian

You've checked that the lever isn't hitting the plate in the lever housing? From memory, which int very good at the best of times, The shaft in the housing on the box has a selector finger clamped to it, is the grub screw tight? and the detent screw and spring may have loosened is it tight . Any old how if you do have to take the box out its all quite easy to get at inside the front output housing.

I have checkrd that it isnt hitting the plate. I am using the box in a trailer so i have good ? access to the linkages. The grub screw was loose initially but after tightening it ,it only improved things slighly. I think the problem may lie within, as an animal of a mate borrowed it recently and tryed to cure the sliff selection with an extended bar slotted over the high/low shift lever. and also by using diff lock on the road. as you can imagine I am not terribly chuffed.
Anyway many thanks for the info

Problem sorted ..the hi/lo selector shaft was semi siezed in the housing cover a good strip down clean and lube has sorted it.
now I can change up and down with 2 fingers (rather than gorilla strength) many thanks for the suggestions.

Bit easier than tekin yer tranny box apart.

definatly........Now Im off to the MOT shop