Once known as the NV 231 and then the NP 231, these two transfer cases are basically identical and share interchangeable parts. Nowadays this transfer case is simply labeled the 231J. The 231J features an aluminum case, chain drive, a driver side front output and centered rear output. It has the lowest low range gear ratio of all Jeep 231J transfer cases at 2.72:1. The major variations of the 231J-transfer case are the input gear which can be found in 21 and 23- spline and a short, medium and long versions of each. The 231J is a very strong transfer case and can be found in a variety of Jeeps since its introduction in 1988. The 231J transfer case is strongly supported by the after market and can be easily upgraded. It can be found in XJ Cherokee's, MJ Comanche's, and YJ Wranglers as the Command Trac transfer case. It has also been the Command Trac transfer case in the ZJ Grand Cherokee since the ZJ's introduction in 1993. The new TJ Wrangler continues to use the 231J except in the Wrangler Rubicon.