The Wrangler YJ was produced with two different transfer cases: the New Process 207 (NP207) and the New Process 231 (NP231). The 1987 Wrangler YJ came with the NP207 primarily because there was a surplus of them when Chrysler took over the Jeep brand. Up until this point, the NP207 was used exclusively in the 1984-87 Cherokee XJ. From 1988 to 1995, the Wrangler YJ was outfitted with the NP231 transfer case.

The NP207 has an aluminum case. It is similar in appearance to the NP231, but should have a tag (facing the rear of the vehicle) that’s stamped New Process Gear Model 207. The NP207 is chain driven. Models mated to a manual transmission have a 21-spline input shaft. Models mated to an automatic transmission have a 23-spline input shaft. The output for the front driveshaft is on the driver’s side. The ratio for high-range is a direct drive 1:1 while low-range is 2.61:1. This transfer case is unpopular due to its weakness when used in modified Wranglers for off-road. Many of the NP207 transfer cases have been swapped out in favor of the NP231 transfer case.

The NP231 has an aluminum case. Conversely, it is similar in appearance to the NP207, but should have a tag (facing the rear of the vehicle) that’s stamped New Process Gear Model 231. The NP231 is chain driven. Models mated to the Peugeot BA-10 or Aisin-Warner AX-5 transmission have a 21-spline input shaft. Models mated to the Aisin-Warner AX-15 transmission have a 23-spline input shaft. The output for the front driveshaft is on the driver’s side. The ratio for high-range is a direct drive 1:1 while low-range is 2.72:1. This transfer case is widely supported in the off-road community due to its strength and ease for upgrading it with parts made by many third-party companies.

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