I work for www.gearcentregroup.com
I sell transfercases, differentials, lockers and all that stuff ALL DAY LONG lol
Many different variations of Transfer case, mainly made by Borg and Warner or New Process.
A stock 4wd truck, without a diff lock in the front or rear is really only a two wheel drive, one wheel has power in the rear, one has power in the front, as both differentials are "open". The Inner nest kit it both diffs will couple and power away from a wheel that gains to much traction, usually. This is why they wear out, and people chew splines and what not on there axle shafts.
AWD basically means it a full time "4x4" vehicle, usually Fully independent drive/suspensoion, much like say on a Chevy Astro van say for instance
GM 7.25 CORP diffs front and back. This gives a better traction advantage, especially on more say gravel.
Thats the gist of it...i could go into Vacuum operated diff locks/electric diff locks, were a small shift collar is engaged to lock that differential into power mode, as, some vehicles regardless of t-case shifter position, still allow for the front driveshaft to rotate.
Damien-they don't make them like this anymore
97 SSEi. 3.2mps,msd,optima,1.9 YTs,245 RE750s,SLP Headers,custom ported SC inlet/outlet, 180 deg, INTENSE pcm,42.5#injectors,255lph pump,custom soilid motor mount, 3.0 mps(maybe), and the nut behind the wheel.