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50-043X : 1997 to current GM 4L60E/4L65E 4wd to theJeep NP231 transfer case,adapter kit. (#50-0434 / 50-0435)

50-043X : 1997 to current GM 4L60E/4L65E 4wd to theJeep NP231 transfer case,adapter kit.

50-0434

Note: This adapter assembly includes a new Jeep NP231 input gear that is 27 splines. This new input gear only fits Jeep NP231 up to model years 1994!!

Advance Adapter:

The 4L60E hex bolt adapter to the Jeep New Process NP231transfer case is 4.00 in length. And the overall length of the transmission and adapter is 25.875”. Adapter material is 356 T-6 heat treated aluminum alloy. The adapter has a provision our H.D. transmission mount. The adapter kit includes a 2 piece adapter housing, Jeep NP231 input gear that is 27 splines , GM VSS sensor, reluctor ring, o-ring, gasket, fastening hardware, and adapter instructions.

Transfer Case:

This adapter assembly will fit the Jeep New Process NP231 transfer case.

Transmission:

The adapter kit is designed for exclusive use with the 1997 & up GM 4L60E/4L65E with a removable bellhousing.

 

50-0435

Note: This adapter assembly includes a new Jeep NP231 input gear that is 27 splines. This new input gear only fits Jeep NP231 1995 & newer !!

Advance Adapter: 

The 4L60E hex bolt adapter to the Jeep New Process transfer case is 4.00 in length. And the overall length of the transmission and adapter is 25.875”. Adapter material is 356 T-6 heat treated aluminum alloy. The adapter has a provision our H.D. transmission mount. The adapter kit includes a 2 piece adapter housing, Jeep NP231 input gear that is 27 splines , GM VSS sensor, reluctor ring, o-ring, gasket, fastening hardware, and adapter instructions.

Transfer Case:

This adapter assembly will fit the Jeep New Process NP231 transfer case.

Transmission:

The adapter kit is designed for exclusive use with the 1997 & up GM 4L60E/4L65E with a removable bellhousing.

 

TRANSFER CASE INFO:

NP231

 

In 1987 Jeep began the gradual introduction of the New Process 231 transfer case. The Np231 was initially introduced in Cherokees, followed shortly thereafter into the Wrangler. Jeep enthusiasts initially received the transfer case with mixed opinions.  Many jeepers hoping for the grand old days of the gear driven Dana 300 were obviously a little disappointed.  Skeptics aside, the medium duty NP231 proved itself reliable and capable for most applications.  The transfer case is by no means perfect, but coupled with aftermarket upgrades; the NP231 transfer case meets the expectations of most jeep consumers.

Identification and Features

The chain driven NP231 was offered with a driver side front driveshaft shaft assembly only. The rear output shaft offer a centered slip yoke design. The slip yoke feature caused the transfer case to be somewhat long at 21.5”.  The Np231 continued to utilize the round circular six bolt pattern as seen on the previous NP207 and Dana 300 transfer cases. The Np231 case was a die cast aluminum 2 piece design. The standard 231 weighs approximately 70 lbs. 

  One of the easiest ways to identify the Np231 is the metal tag located on the back of the transfer case.  This red and silver tag offers some valuable information concerning the transfer case. This tag indicates from top to bottom: the model type, production build #, date, and lastly 2:72; identifying the standard low range for the Np231.

  The input shafts were available in either 21 or 23 splines.  These inputs were further offered with a short or long design.  These variations were determined by year, engine size, and transmission options. The chart below gives a general breakdown of not only length and spline count but also includes a pitch difference found on the internal planetary gear portion of the various input shafts.

The Np231 operates as 4 basic functions: 2H, 4H, N and 4 low. Since the transfer case is a chain driven design, a true twin stick is not functionally available.  There are internal aftermarket kits available which allows for a 2wd rear low only function.

The speedometer feature of the NP231 can be broken down by three different styles. The speedometer was always located in the rear nose cone of the NP231. The 1987-1991 used a standard mechanical drive which basically turned a cable. In 1992, The Np231 featured a similar mechanical drive however the spinning gear was converted to a digital square wave signal.  The interchangeable plastic gears were the same as previous mechanical units. These replaceable gears allow the consumer to quickly and easily recalibrate their speedometer when doing common tire and ring and pinion changes. The TJ introduced a similar vehicle speed sensor (VSS) however the speedometer drive used a new shorter gear assembly.

 

Strength and Upgrades

  The NP231 has long been the topic of many campfire debates as well as internet forum arguments.  There has been much discussion as to the strength of this transfer case. In some corners, the transfer case has been proven durable and dependable; capable of handling V8 power, larger tires and moderate off-roading.  For others, they view the transfer case as problematic with questionable manufacturing design choices.  Both ranges of opinions hold some validity.  Luckily with the support of the aftermarket, numerous fixes and upgrades are available. These include wider chains, heavy duty planetaries, low range gears, and fixed yoke kits. The most common upgrade to the NP231 by far is the “fixed yoke kit” also known as an SYE (slip yoke eliminator). More information can be found  here PNNP231-SYE concerning the NP231 fixed yoke kit.

  These upgrades eliminate certain pitfalls and clearly strengthen the transfer case.  For some off roaders, the cost of upgrades with limited results just doesn’t fill the void compared to a gear driven transfer case.  The consumer should heavily weigh his driving style, build choices, and most importantly: his options.  We have seen many Wrangler owners who have installed numerous upgrades including lower gearing to the tune of $1600-$1800 only to replace the transfer case.   Aftermarket transfer cases such as the Atlas have brought back dependable gear driven options to the market.

TRANSMISSION INFO:

 

GM 4L60E Transmissions 

GM manufactures this transmission in two versions. Both these transmissions use a reluctor ring connected to the GM engine computer for proper shifting points. The first version is a mirror image of the 700R/4L60, but it requires the reluctor ring. The second version is found in most of the 1997 & newer vehicles. The case and bellhousing are no longer cast together (now a removable bellhousing design). This transmission no longer has the square bolt pattern on the output side, but is equipped with a hex bolt pattern similar to a TH400.  

4L60E 4 bolt tail housing early design 1993-1996  Available in the same two case designs as 700R4 metric (60 degree V6) and 90 degree Chevy V6/V8. This transmission looks the same as a 700R4/4L60 but has a large round electrical plug on the passenger side of transmission and no T.V. cable was used. This transmission shifted by the engine PCM. There are aftermarket stand alone shift controllers available for the 4L60E. The one we recommend is the Compushift controller which we carry under our Part# P4L110.  

This transmission needs 40 pulse per drive shaft revolution (VSS) for proper shifting. GM installed a VSS sensor in the transfer case on 4x4 models and in the tailhousing on 2WDs. A low range switch is used on 4WDs to send a signal to the computer that the VSS must be adjusted for the transfer case low ratio. We design most of our adapters to have a VSS sensor in front of the transfer case. This allows the computer to always see a accurate reading from the VSS and keeps the transmission from having shifting problems. The sensor can be located after the transfer case; however, the computer must be programed to accept the transfer case low ratio. Stock GM transfer cases have a stock ratio of 2.72:1.   

4L60E late removable bellhousing design  

In 1997, GM changed the 4L60E transmission case to a removable bellhousing design. This was so one transmission case could fit all GM engines including LS series of motors. Care must be taken due to different torque converter bolt patterns and length for each of the bellhousings. The stator and input shaft also had some variations. Be careful interchanging bellhousing and converters on these transmissions. The length of the main case is shorter and now has a 6 bolt pattern on the tailhousing. The case length including bellhousing is 21.735" on Gen I and II V8 and 22.366" Gen III / LS V8. In 2001, GM introduced 4L65E (HD version of 4L60E). This included a 5 pinion planetary gear set vs. 4 pinion in the 4L60E. The 4L70E was introduced with even more upgrades which included stronger output shafts and reaction shells for use in GTO, Silverado SS, Trail Blazer SS, and other high performance vehicles. 

Forward Speeds               ....            

Dates Produced                ....           1993 - 2007 

Manufacturer    ....           General Motors                                 

Case Length       ....           23.375 (1st gen) 15.435 (2nd gen)

Bellhousing Length          ...            Integral (1st gen)  6.315" (2nd gen)

Over All Length ....           23.375 (1st gen)  21.750 (2nd gen)

Case Material    ...            Aluminum                            

Output Shaft Spline        ....           27                            

1st Gear Ratio    ....           3.06

2nd Gear Ratio  ....           1.62

3rd Gear Ratio   ....           1.00

4th Gear Ratio   ....           .696  

Transmission Weight      ....           195LBS (1st gen)   163LBS (2nd gen)

Max Engine Torque         ....           360 to 400                             

Fluid Type           ....           Dextron VI

Fluid Capacity    ....           11 Qts

Gross Vehicle Weight Rated        ....           8600

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