Building A Better Transfer Case: NP231JPosted in How To: Transmission Drivetrain on October 1, 2010
The NP231 transfer case was introduced in the mid '80s on Jeeps and has been the staple in a number of four-wheel-drive vehicles ever since. The NP231 has 2H, 4H, Neutral, and 4L. When Chrysler took over Jeep this transfer case was coined the NVG 231J, or simply the 231J. The transfer case is a light-duty chain-driven unit that is very popular amongst four-wheel enthusiasts because of its rugged dependability.
The fulltime NP249 transfer case in our '97 Grand Cherokee works well in stock form, but needed to be swapped out because it's not as good for medium-to-hardcore wheeling. The NP249 can be found behind '93-'98 Grand Cherokees and has 4H, Neutral, and 4L. Some of the earlier units are known to have issues with viscous coupling, which acts as a limited slip inside the case. We personally don't care to drive around in four-wheel drive in normal driving conditions either, as it's tougher on the tires and drivetrain and can effect fuel economy.
We contacted JB Conversions regarding the swap for our Grand Cherokee. The company recommended the complete HD 231 transfer case, including a slip yolk eliminator tailshaft. Since we love to put things together ourselves, JB Conversions sent us everything needed to assemble the 231J, including new case halves. The result of this build is a high-quality transfer case that's perfect for a high-horsepower engine and tough four-wheel conditions.