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Old October 24th, 2006, 08:51
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woody woody is offline
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Join Date: May 2002
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What transfer case do I have?

The following 4WD transfer cases were utilized on the various XJ/MJ models throughout the production run.

New Process NP207 Command Trac: 2-speed, chain-drive, part-time 4WD. 2:72:1 low-range. 84-86 2.5l 4cyl and 2.8l V6 models with manual or automatic transmissions. 21-spline input. These used a vacuum switch to activate the dash indicator lamp and engage the front axle disconnect. The shift indicator pattern is 2WD > 4WD high range part-time > Neutral > 4WD low range part-time.

New Process NP229 Select Trac: 2-speed, chain-drive, part or full-time 4WD. 2:72:1 low-range. 84-86 2.8l V6 models with automatic transmission only. 21-spline input. The shift indicator pattern is 2WD > 4WD high range part-time > 4WD high range full-time > Neutral > 4WD low range part-time.

New Process NP231 Command Trac: 2-speed, chain drive, part-time 4WD. 2.72:1 low-range. 87-01 2.5l 4cyl and 4.0l I-6 models with manual or automatic transmission. 87-89 21-spline input, 90-01 23-spline input. The older models used a vacuum switch to activate the dash indicator lamp and engage the front axle disconnect. Newer (non-disconnect axle) versions used an electrical switch to activate the dash lamp. The shift indicator pattern is 2WD > 4WD high range part-time > Neutral > 4WD low range part-time.

New Process NP242 Select Trac: 2-speed, chain-driven, part or full-time 4WD. 2.72:1 low-range. 87-01 models with 4.0l I-6/AW4 automatic transmission only. 87-89 21-spline input, 90-01 23-spline input. The shift indicator pattern is 2WD > 4 high range part-time > 4 high range full-time > Neutral > 4 low range part-time.

Common to all New Process/New Venture transfer cases is an round ID tag on the rear case half. This will indicate the model and serial number. OEM Jeep transfer cases are indicated by the "J" designator (ex: NP231 J) and other OEMs had their own designators (C= Chevy, D= Dodge, AMG= AM General etc...) there is some crossover between parts within the various OEMs, but I won't get into that here.

Throughout the production run, input spline counts and other internal specs changed, and must be compatible with the transmission it's mated to. The later model cases (1996.5 and newer) changed styles of rear slip yoke to an internally sealed version. When replacing parts, performing upgrades, or replacing the case entirely, one must take care to insure the new parts/assemblies are compatible with what is in presently.
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