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Starting in about 1987, the New Process 231/241 series transfer case became standard in Jeep, Dodge, and Chevrolet applications. These transfer cases are part time 4WD (Shift positions 4HI - 2HI - N - 4L). They have a relatively thin aluminum housing. They are 1:1 direct drive in high range, and use planetary reduction gears for low range with a ratio of 2.72:1 They use chain drive for the front output. The NP241 was typically used in V8 applications. The 231 is a lighter duty case than the 241 series cases, and was typically used in 4 and 6 cylinder Jeep, Dodge and Chevy 4x4 vehicles. It is a part-time 4 wheel drive case.
Exact identification:
These New Process cases have a circular plate, about 2" in dia., on the rear of the case, in the center. Full identification info for the case is on this plate
Bolt Pattern:
Jeep, Dodge and Chevy versions all use a 6 bolt circular bolt pattern.
This pattern is NOT symmetrical and will only bolt up one way. You can
typically bolt a Jeep unit to a Dodge transmission and vice versa, however
Chevrolet units are NOT cross compatible: While GM uses the same 6 bolt
patter, they have it rotate approximately 90 degrees from that used by
jeep dodge.
In all of these 6 bolt applications the Klune-V Extreme Underdrive will
bolt up to these transfer cases directly with adapters necessary. Some may
require a spacer.
Slip-Yoke Eliminator
All of these units we have seen have been equipped with a slip-yoke rear output. Slip-Yoke Eliminator kits are available for most of these transfer cases
Jeep / Dodge NP231 units:
All of these cases have a left hand drop (front drive
shaft on driver's side).
Input Spline: These T-cases come with either a 21 or 23 spline female input. The 21 spline shaft is frequently found in 4 cylinder applications and the 2.8L V6, While 4.0L 6 cylinder and 8 cylinder applications always used the 23 spline input shaft.
GM New Process 231 Transfer Case
Most of these units will be right hand drop, but
Chevy also used a few left hand drop applications. The Chevy NP231 is
supplied with a 27 spline female input.