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Jeep Transfer Cases

Old 12-10-2008, 05:16 PM
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Year: 1992, 2- 1998 (All 3, 4 Doors)
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Engine: 4.0L in all
Default Jeep Transfer Cases

Transfer Cases

The transfer cases used are all chain driven with aluminum housings. NP stands for New Process which is the brand, if you will. The newer ones are NV instead which stands for New Venture. It is the same transfer case just a different name.

NP207: "Command-Trac", Part-Time only, 2.61:1 ratio low
The NP207 has a aluminum case and an appearance similar to the NP231. It should have a tag on the back saying New Process Gear, Model 207. This chain driven transfer case uses a 21 spline input with the manual transmissions and a 23 spline input with the automatic transmissions. The output for the front driveshaft is on the drivers side. Low range is 2.61 and high is 1.00. This transfer case is widely scorned. If yours should break, look for a 21 spline NP231 or swap transmission and transfer case at the same time. The transfer case is upsidedown in the picture showing the input (it is drivers drop.)

Usage
The NP207 was used in the first year of Wranglers in 1987. It was used in Cherokees (XJ) until from '84-'87.
NP231: "Command-Trac", Part-Time only, 2.72:1 ratio low
Pattern: 2HI - 4HI - N - 4LO
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.

Usage
Since 1988, the NP231 has been the "Command Trac" transfer case used in Cherokees (XJ), Comanches (MJ), and Wranglers (YJ). It has been the "Command Trac" transfer case in the Grand Cherokee (ZJ) since its introduction. The new Wrangler (TJ) continues to use the NP231, but the NP231 used in the TJ has a different tail housing that allows the removal of the drive shaft with out losing transfer case fluid.

Both version of the NP231 used in the Wranglers have an over all length that is long for a short wheel base vehicle. This can cause driveline vibration and premature u-joint failure especially for a lifted vehicle. There are kits to convert the tail housing to a standard yoke to allow the use of a longer rear drive shaft. There is also a 4:1 low range reduction kit for the NP231. Wrangler are only available with "Command Trac", so the NP231 or NP207 are the only transfer cases available from the factory in any Wrangler model.
NP228/NP229 - "Selec-Trac"
The NP228/229 transfer cases were Jeeps first transfer cases to receive the "Selec Trac" name, the later Selec Trac transfer case being the NP242. Both the NP228 and NP229 offer 2 wheel drive, Full Time 4 wheel drive in High range and Part Time 4 wheel drive in Low range. The NP228 uses an open differential for its front/rear power split in 4WD Fulltime High, the NP229 uses viscous coupling for its front/rear split in 4WD Fulltime High. Both lock the front/rear output shafts in 4 wheel drive in Low range. Both lack a 4 wheel drive Part Time High range mode.

The NP228 was offered in '85-'87 XJ Cherokees.

The NP228/229 use 2 controls for its various modes. A vacuum switch controls 2 wheel drive or 4 wheel drive. A shift lever controls High or Low range.
NP242: "Selec-Trac", Full or Part-time, 2.72:1 ratio low
Pattern: 2HI - 4HI (P/T) - 4HI (F/T) - N - 4LO
The NP242 has an aluminum case and it should have a tag on the back saying New Process Gear, Model 242. New versions of the NP242 are refered to as NVG242 or NV242 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.

The chain driven NP242 is a full time transfer case with a 48/52 torque split front and rear. It is possible to lock it into four low so it behaves like a part-time transfer case. When it is locked in, power will be split regardless of traction. The output for the front axle is on the drivers side. Low range is 2.72 and high is 1.00.

Usage
The NP242 is used in Grand Cherokees (ZJ) and Cherokees (XJ).
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Decoding NP/NVG transfer cases

Decoding New Process/New Venture transfer cases is fairly simply, each transfer case has a 3 digit number, like 231, 241, 242, etc.
These numbers will tell you the basics of that particular case.

First Number:
The number of speeds.
If it is a standard high-neutral-low transfer case, the number is 2.
If it is a single speed with no low range, it gets a 1. i.e.: NP133

Second Number:
The size of the case, physically, and it's strength.
The currently used case sizes are: 2, 3, 4, 6, 7.
With X2X series being the smallest, and X7X series being the largest of the production lines.

Third Number:
The third number pertains to what type of 4wd system is used in the case.
Current systems used are designated by: 1, 2, 3, 4, 6, 7, and are described as follows:

1: Part time, Manually shifted.
When in 4WD, the front and rear driveshafts are locked together.
If its a 2 speed transfer case, then it will have 4 positions, 2WD-4WD-N-4LO.
These cases are manually shifted by a lever on the floor.
Popular examples: 231, 241, 261, 271

2: Full time/Part time, Manually shifted.
A geared differential is used to allow the driveshafts to turn at different speeds, while still applying torque.
Some are 4 position, and some are 5:
4 position cases have 4FT-4PT-N-4LO.
5 position boxes get a true 2WD, where the front differential is bypassed, and all the torque goes to the rear driveshaft.
These cases are manually shifted by a lever on the floor.
Popular examples: 242, 242HD, 242AMG

3: Part time, Electronically shifted.
Same as the 1 designation, except an electric motor is used to shift the transfer case in and out of it's ranges, either with a button or a dial easily accessible to the driver.
Popular examples: 133, 233, 243, 263, 273

4: Full time/Part time, Electronically shifted.
Same as the 2 designation, except an electric motor is used to shift the transfer case in and out of it's ranges, either with a button or a dial easily accessible to the driver.
Popular examples: 244

5: Not Currently Used.

6: Active On Demand System.
Front and rear axles are constantly monitored electronically to detect any differences in speed due to wheel slippage. When a speed difference is detected, the computer signals a transfer case clutch-pack to engage. Torque transfer is transparent to, and independent of, the driver.
Popular examples: 226, 236, 246

7: Progressive On Demand System.
The vehicle normally operates in 2WD. When traction is lost by one of the driving wheels, power is automatically transferred to the other axle. Torque transfer is transparent to, and independent of the driver.
Example: 247

Last edited by BowtieGuy3; 01-07-2009 at 10:35 PM.
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