YJ Transfer Case ID: NP207 vs NP231
The Wrangler YJ used two New Process transfer cases. 1987 YJs got the NP207 (Chrysler had a surplus from the 1984–87 Cherokee XJ). 1988–1995 YJs got the NP231. The two cases look alike from a few feet away. The ID tag, the year, and the low-range ratio tell them apart.
How to tell NP207 from NP231
- Read the tag on the rear of the case (facing the back of the Jeep). It is stamped New Process Gear Model 207 or Model 231.
- If the tag is missing: a 1987 YJ is almost certainly an NP207; 1988–95 is an NP231 unless someone already swapped it.
- Low range is 2.61:1 on the 207 and 2.72:1 on the 231.
| NP207 | NP231 | |
|---|---|---|
| Years (factory) | 1987 YJ only | 1988–1995 YJ |
| ID tag | Model 207 | Model 231 |
| High range | 1:1 | 1:1 |
| Low range | 2.61:1 | 2.72:1 |
| Front output | Driver side | Driver side |
| Manual input | 21 spline | 21 spline (AX-5, BA-10) |
| Auto / AX-15 input | 23 spline (auto) | 23 spline (AX-15 / auto) |
| Aftermarket | Weak; often swapped for a 231 | SYE kits, slip-yoke, lockup |
NP207 (1987)
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.
NP231 (1988–95)
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. The Rubicon Express SYE install on this site is for the NP231.
Shop transfer-case and SYE parts on eBay drivetrain and the Amazon driveline catalog.
New Process 207 (NP207): Installed only in the 1987 Wrangler.
New Process 231 (NP231): Installed in all Wranglers from 1988–95.