Four Wheel Drive Operation (4WD) - YouTube explains how the 2007-2013 Toyota Tundra 4WD system works. Front propeller shaft (and transfer case chain) does not rotate in 2WD assuming the automatic disconnect differential is working properly. 5th generation 4Runner is similar except for the Limited and Nightshade which are full time 4WD. The video shows actual hardware with cut outs showing internal details and how the system works. You'll know a lot after watching it.