"The NP228 had a direct-drive 2wd mode. It used an internal, open differential for four-wheel-drive mode and high range and featured a fully locked mode in four-wheel-drive, low range. It featured vacuum actuation for mode operation and a conventional shifter linkage for range operation. This transfer case was used in the XJ Cherokees as the optional in lieu of the NP207.
The NP229 was similar to the NP228, but it featured an internal viscous coupling for full-time operation. This transfer case was offered in the FSJ Grand Wagoneer."