If you are familiar with New Process/New Venture Gear transfer cases, you know that the first number indicates the number of speeds, the second number denotes the torque rating and the third number is the differential type. So, the 231 is a 2 speed transfer case with a high and low range, with an arbitrary torque rating of "3", and a locked center diff (not actually any differential at all). For street driving and drag racing where you are looking for minimal weight and rotational resistance, it doesn't make sense to have a low range, however, it is beneficial to still be able to select between 2wd and 4wd. While there are many transfer cases that will bolt up to the existing NP transfer case mount on my TH400, none of them offer selectable locked 4wd and 2wd, without low range. I had a nice condition 231J from a liberty taking up space so I decided to tear into it. This particular case has a 31 spline output shaft, so its a bit stronger than the 242 I was using previously. After opening the case the process of deleting the low range was simple. Ditch the fork and planetary gear set, cut the ring gear out of the case, take the teeth off the input shaft (which is the sun gear of the planetary set), and make a spacer for the main shaft which will keep the low range selector slider permanently engaged. After a little clean up on some of the other parts, re-assembly was just like any other 231. After I pulled the 242 out of my XJ, I weighed both cases with a scale, dry. The 242 comes in at 83 lbs, while the "131" comes in at 51 lbs. Unfortunately I did not have a stock 231 on hand to weigh, although I only expect it to weigh a few pounds more. The real advantage comes from the decreased rotational inertia. I expect this case to absorb a bit less power than the 231 and 242 cases.

 

 Taking the teeth off the input shaft