3rd gen trans box

[kpautos]

probably been done 300 times so please forgive me and let me know where and i will go away and read it all!!
3rd gen auto
wont move unless you engage diff lock and then it only has power to front wheels
turn rear prop and you can hear and feel a noise as if its not engaging inside trans box
question is... does the vac unit at the rear engage the drive to rear prop or is it to do with engaging the front prop/diff lock?
noise is 100% coming out of trans box not rear diff
any help would be great, thanks, kirk

[kpautos]

quick update, removed prop and rear flange/extension housing, can see the trans box chain and if you turn prop it remains static, its as if the trans box is in nuetral but it cant be as the front prop is being driven
looking like a replacement trans box........

[kpautos]

Deffo stuck/broken as I removed rear prop and it still drives!!