03-13-2006, 03:30 PM
Jack Lives Here!!!
WF Supporting Member
Join Date: Apr 2005
Location: Phoenix, AZ
However, the following information from the site provided is very important. As you can't just swap a 21 spline from a 4 cyl to a 23 spline from a 6 or vice versa. You have to swap the input shaft also.
The NP231 has an aluminum case and it should have a tag on the back saying New Process Gear, Model 231. New versions of the NP231 are refered to as NVG231 or NV231 which stands for New Venture Gear. The tag on the back of the transfer case will reflect the name change. Only the name is different. A NV231 HD model is used in some ZJs. Presumably this is a "heavy duty" version for Jeeps with the big V8s.
There are versions of this chain driven transfer case that take 21 and 23 spline input shafts. The 23 spline version is used behind the AX-15 and the 21 spline is used behind the AX-5 and the BA 10/5. The output for the front driveshaft is on the drivers side. Low range is 2.72 and high is 1.00.
If you own a 21 spline NP231 and you want to swap in a 23 spline transmission, you can either look for a cheap 23 spline NP231 at the junk yard or go to your local Jeep Parts Dealer and order up a new input shaft part #5300-6085. This is the part you need to convert your NP231 to 23 spline input.
How big is this crack in your case? More implortantly how did it crack? If it's pretty small there wouldn't be any harm in just JB welding it up so that it won't spread or leak on you.
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