[Горыныч]

ХМ, а вот в патенте (вроде она) другая инфа:

A transfer case for a four wheel drive vehicle providing a central shaft defining a first output concentrically surrounded by a forward high/low drive range gear set and an aft dual planetary inter-axle differential gear set. A range clutch collar is disposed between the gear sets for selectively providing four wheel drive low range, neutral, and full-time four wheel drive high range. Likewise, a mode sleeve is disposed between the gear sets for selectively locking the differential gear set when the vehicle is shifted into its four wheel low range. Inner and outer relatively rotational drum housings surrounded the aft dual planetary differential gear set for defining an annular viscous fluid coupling chamber therebetween. The inner drum is formed with internal annulus gear teeth meshed with a portion of the dual planetary gear set for rotation with the first output shaft while the outer drum is interconnected to a second output for providing full-time four wheel drive differentiation with limited slip between the first and second outputs.