Imp, one thing that is up in the air, does removing the front shaft increase fuel mileage? I have always thought no, and that removing it was ridiculous when you can just get a RWD Explorer.
In my own Explorer, which has 3 choices by switch: 4WD AUTO, 4WD HIGH, and 4WD LOW, the front driveshaft, front gears, and front axles must turn whenever the vehicle is moving. Removal of the front shaft, as I see it, would eliminate only the frictional losses and inertial effects due to the front U-joint, rear C-V joint, and the weight of the shaft and parts. If the difference in fuel consumption amounted to more than 1%, I would be surprised.
OTOH, the earlier Explorers like my '96, which had the vacuum-operated axle-disconnect which I THINK allowed the driveshaft (and consequently, the axleshafts, to "free-wheel", the axles still having to rotate whenever the vehicle was in motion. The switch to 4WD in the '96 was accomplished by energizing an "electronic clutch", which drove the front driveshaft, in both 4WD HIGH and 4WD LOW. The vacuum-disconnect threw in one more part which could cause loss of 4WD if it failed. Still, in 2WD, it likely saved again, my guess, less than 1% in fuel economy. My 2004 has essentially the same system, with the only difference being front/rear speed sensing to turn on the T.C. clutch automatically in 4X4 AUTO, that selector replacing 2WD in the '96.
Obviously, the best set-up would be locking hubs, which eliminate axle rotation altogether (AND driveshaft rotation). With manual hubs and manual T.C., one could engage 4WD HIGH or LOW, with hubs UNLOCKED, and drive was through rear wheels only. I did that now and then, in LOW, to achieve very slow speed, but not needing 4WD, for very short distance. When that was done, the front axle shafts turned within the unlocked hubs.
The AWD T.C. is actually a much simpler system than either of the above, having no gear choices, no switches, but rather a slippey-slidey viscous coupling driving the front wheels. The often-quoted "torque-split" between front-rear, sometimes quoted as 65% rear, 35% front, actually varies with the tractional difference between axles, but will never be 50/50, because the lesser torque delivered to front wheels is explained by heat generated within the viscous coupling. imp
