I was thinking about doing this on my wife's 99 expo 4.0, but since hers doesn't have a CAD or lockouts it doesn't change anything, especially for wear. All the components will still be moving, they just will be coasting instead of having power supplied to them. I can't imagine a CV of u-joints life span being affected much by having it coast vs. handle power. Lets face it the 4.0 isn't much of a joint snapping power plant.
Excerpt from a site I found in my research:
"'97-'01(switch says, 4auto, 4high, 4low
The '97-'01 model years lack a true 2 wheel drive option. With a live front axle, there are no significant mileage gains to be had by driving the rear wheels alone. That being said, some of us simply prefer to determine when the front wheels should drive and when they shouldn't, instead of relying on a computer to make that decision for us."
If you can read this, thank a teacher. If you can read it while pooping, thank Bill Gates!
"A girls butt hole is like a 9 volt battery. You know its wrong, but eventually you put your tongue on it."