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As mentioned above, 4 full-time is the same basic idea as AWD and you can use this anytime on any condition. However, there is no viscous coupling or any type of limited slip in regards to transferring power between the front and rear tires. The transfer case functions as an open differential between the front and rear axles (we did testing on vehicles equipped with this transfer case for years, and I just glanced through a factory service manual to verify)......no clutches, no viscous coupling, just an open diff....at least for the Jeep/Dodge/Chryler versions.
This means that you can have a "one wheel peel" going on when in full-time 4wd mode, and I've personally seen this. Again, we intentionally performed a durability test on a wetted uphill grade where a vehicle took off at wide open throttle from a stop, which caused only the left front wheel to spin like mad. Also, if you pulled either the front or rear driveshaft the vehicle would not move unless in 2wd or locked in 4wd.
Several versions of this transfer case were used over the years. Included are "4 position" and "5 position" versions in both manual and electronic shift models. The 5 position versions had 2 hi, 4 FT, 4 PT, N, 4 lo. The 4 position versions eliminated the 2 hi option, normally electronic shift, and where used in heavier vehicles like the V-8 Durangos. This version was called the 244. They also tried a 144 version that eliminated low range, but I don't know if that ever made it into production. (Note the name changing from "2" to "1" which denotes 2 gears, hi and lo range, to just 1 gear).
Jeeps did use other versions of transfer cases with various forms of limited slip and viscous couplers including the 249 (optional in the ZJs) and the 247 (optional in the WJ's). Both of these had a direct drive to the rear wheels, and the viscous coupling applied power to the front as needed.....meaning you could pull the front shaft and they would deliver power to the rear wheels with no slippage.
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