Adapting the

GM 4L80-E Transmission

to the

Jeep Models 207, 231, 242, 249 & 241OR Transfer Cases

Novak's 4L80E transmission to the Jeep New Process (or New Venture) transfer cases conversion makes for one of the strongest geartrains possible for both on-road and off-road, and has become an increasingly popular transmission to transfer case combination.

The adapter is compact at only 3.0" long for a combined transmission and adapter length of 29-1/4" (equivalent to a ~22-5/8" manual transmission). The adapter itself is machined of a 6061 aluminum alloy, featuring thick flanges and a heavy cross-section.

There are two different styles of kits to join a 4L80E to your New Process transfer case:

  • "A" kit: replacement 4L80E output shaft version, 23 splines, keeping your 23 spline NP2xx transfer case input gear
  • "B" kit: replacement NP2xx input gear version, 32 splines, keeping your 4L80E 32 spline 4wd output shaft

Option A: 4L80E Output Shaft Replacement

Adapter kit for 4L80E to Jeep transfer cases

Kit 4L81-A, adapting 4L80E transmissions to Jeep New Process transfer cases, 23 spline output shaft version

The 4L81-A adapter is compatible with all versions of the 4L80E. If you have a 2wd 4L80E, a 4wd 4L80E that is undergoing a rebuild anyway, are unsure what 4L80E you have (or will have at the time of the conversion), are missing the rear speed sensor, or your transfer case was just rebuilt (doesn’t leak) and you’d rather not open it back up then the 4L81-A kit is your best choice. The new 23 spline 4L80E output shaft is machined from stock material through an extensive process ensuring maximum strength and a precise fit. The new Novak shaft splines directly into the OEM style input shaft of a 23 spline transfer case. The 241OR Rubicon must use the 23 spline output version. This requires disassembly of the transmission, and we recommend the services of a transmission professional.

The basic installation is a 2-2.5 hour bench job and will include at least simple gasket and seal replacements. Be sure that if your transmission is missing the output speed sensor it is added at this time. See below for the correct parts. This is a good time for a more thorough master rebuild and update of the Hydra-Matic.

Early vs Late 4L80E Oiling

In about 1997, GM changed the way the rear bushing is oiled in the 4L80E transmission. The shafts are not interchangeable and you will need to identify for sure which version you need.

  • The first design has two lube holes in the sides of the case bushing journal. Lube flows through these feeding the output shaft and forward to the planets.
  • The second design does not have the lube holes instead has a tube feeding oil from the valve body.
4L80E Transmission Output Shaft Lube Hole

4L81-A Kit Contents

  • Adapter housing
  • Transmission output shaft, 23 splines
  • Seal spacer
  • Seal
  • Adapter gasket
  • Seal ring
  • Fasteners
  • Steel foot for rear mount
  • Instructions

Option B: Transfer Case Input Shaft Replacement

Adapter kit for 4L80E to Jeep transfer cases

Kit 4L81-B, adapting 4L80E transmissions to Jeep New Process 231, 242, 249 transfer cases, 32 splines

There is a factory 4wd version of the 4L80E which is ready to bolt up to our 4L81-B adapter kit. It features a 32 spline output shaft which protrudes about 3" from the rear face of the 4L80E transmission main case. If you have this version, disassembly of the transmission is unnecessary but disassembly of the transfer case is necessary to install the provided input gear.

The input gear installation is a 2-3 hour bench job and usually includes either a simple gasket and seal replacement or a full rebuild with chain if the transfer case has many miles on it. Transfer case rebuild kits are available. See Related Products, below.

Early vs Late Input Gear Style

The NP/NVG input gears are divided into early and late styles around 1993-1994. There are no guarantees that this change was a clean break pre-1993 vs. post-1993, or that your Jeep's transfer case hasn't been swapped by a previous owner.

If in question, the input bearing width on these models is a good indicator. “E” Early uses a 24mm wide bearing and “L” late is 16mm wide. The adjacent photos show the differences in width of the bearing location and the stepped shoulder between the bearing and the gear.

The 241JK transfer case is a late cut gear, requiring a specially machined shoulder, provided if you choose this option in the above kit.

4L81-B Kit Contents

  • Adapter housing
  • Transfer case input gear, 32 splines
  • Seal spacer
  • Seal
  • Adapter gasket
  • Seal ring
  • Fasteners
  • Steel foot for rear mount
  • Instructions
New Process Wide Bearing Input Gear
Early Style
Input Gear
New Process Narrow Bearing Input Gear
Late Style
Input Gear

Applications & Compatibility

Compatible NP & NVG Transfer Cases

The adapter kit is designed for compatibility with 23 spline Jeep NP207, NP231, NP242, NP249, NP241 & NP241OR "RockTrac" transfer cases. Below is a summary of spline counts and lengths usually encountered.

Transfer case seal spacer
New Process input gears come in varying spline counts and lengths. Whichever you have, we've got you covered. A seal spacer sleeve is included and pre-installed in your Novak adapter in the event your transfer case has a short input gear.
  • NP 231 - The NP231 may have 21 or 23 splines and a long or short style input gear
  • NP 242 - The Jeep version NP242 may have 21 splines for the 1987-1990 versions. When connected to the 4.0L HO engine (1991- ) the 242 will have 23 splines as will the Dodge and later V8 Grand Cherokee, AMG versions are 32 splines long
  • 249 - The NP249 always has 23 splines, but may have a long or short style input gear
  • 241OR - The RockTrac will always have a 23 spline, short style input gear. Its gear is unique and not interchangeable with any of the other versions due to the lower 4:1 ratio
  • NP207 - The NP207 may have 21 or 23 splines. Many versions feature extra-long input gears whose stick-out lengths (as measured from the front edge of the input gear to the transfer case front mounting face) longer than 2.2". These will require shortening with a cut-off saw and/or lathe and finished with edge breaking chamfers. New 23 spline NP207 input gears are available in Related Products below.

A more detailed discussion of New Process input gears is found here.

No 21 Spline Version?

The 21 spline shaft is substantially weaker than the 23 spline version. 21 spline versions were only used in the 4 cylinder applications and some very early automatic 6-cylinder versions. Novak does not make a 21 spline version of this adapter kit because of this weakness, vs. the torque created by this transmission.

Our recommendation is to change the transfer case input gear to a 23 spline version. See Related Products, below.

Compatible Transmissions


All versions and years of the 4L80E can be adapted to the NP (New Process) transfer cases. Both the 2WD and 4WD versions work equally well with the correct adapter option.

Output Shaft Speed Sensor

4L80E rear reluctor speed sensor

1991 - 1996 4L80E's should feature a speed sensor at the driver's side rear portion of the case (see image, below), whether they are 2wd or 4wd applications. 1997 and later 4wd applications often omit the rear sensor as this data is available from the transfer case output shaft in factory applications. This adaptation requires that this sensor and its internal reluctor ring be installed by a transmission building professional for proper operation.

See Related Products, below.

Compatible Jeeps

This conversion is compatible with all longer wheelbase (CJ7 93.4” or longer) or stretched Jeeps. The TH350 is the only real automatic option practical for CJ5 and other short wheelbase Jeeps.

These are exceptionally strong transmissions native to 3/4 ton truck and SUV applications. Full Size Jeeps such as Wagoneers, J-Trucks, etc. are conversion candidates for them. There are numerous upgrades available for the 4L80E should stock strength come into question.

Compatible Engines

Any engine that can be made to work with the 4L80E will work with this adapter. Natively compatible engines such as the 1997-2006 Vortec / LS / Gen III+ engines are far and away the most popular choices.

Keep in mind that if you depart from a native configuration on the engine, you will need an aftermarket controller for the transmission as these are electronically controlled both in the shifting and pressure. Without a controller you’ll only have reverse, third gear and max line pressure; probably not the best solution for a Jeep.

Lastly, be aware of Gen III engine crank spacing, 4L80 flexplates, and torque converter heights. This is not much of an issue where installers have pulled a factory matched engine / transmission combo as their donor, whereas those who are mixing and matching LS components should verify accordingly. We've written a helpful guide to GM crank spacing here.

Transfer Case Clocking & Rotation Options

Our adapter is drilled for multiple clocking locations. However, most New Process transfer cases will clock to a near-factory angle.

Rear Mount Provision

This transfer case adapter's design features a modular mounting and support system and mounting base, ready to accept our industry standard urethane isolator mount, available in Related Products, below.

Related Products

Urethane Rear Mount for Crossmember
4L80E Output Speed Sensor OSS
Transfer Case Input Gear, 23 Spline
Transfer Case Input Gear, 23 Spline
4L80E 4wd output shaft
4L80E 4wd output shaft
Auto transmission cooler
1976-1986 Jeep floor tunnel cover
NP231 transfer case parts
NP242 transfer case parts
Slip Yoke Eliminator for NP231 Transfer Cases
TurnKey 4L80E Transmission Package

Installation Requirements


The automatic transmission takes more specialized tools, knowledge, gaskets, seals, and snap ring pliers, etc. Installation after the output shaft is in place requires normal mechanics hand tools.

Rear Mount Provision

This transfer case adapter's design features a modular mounting and support system and mounting base, ready to accept our industry standard urethane isolator mount. See Related Products, above.

Powertrain Placement

As these usually are installed as part of an engine swap setting the powertrain to the proper pitch angle - usually tilted down ~5 (3-7 acceptable) degrees - is recommended. Offset will be to the right (passenger’s) side because of the driver drop transfer case and front differential usually 1 to 1-1/2”. Consult our engine conversion guides for more specific recommendations on placement if the engine is being replaced.

Clocking Information & Driveshaft / Yoke to Pan Clearance

Our adapter is drilled for multiple clocking locations and driver’s side drop transfer cases usually clear nicely in most all applications. Yoke and driveshaft clearance is usually ample.

Engines & Engine Mounting

GM Engine Mounts for JeepsNovak engine mounts are available to ease the installation of your GM V6 or V8 engine. Novak has engines mounts for most Chevy, Buick and GM Gen III+ V8's.

Novak's engine mounts, feature vibration dampening, superior strength and useful adjustability - adjustable even after the engine is installed. The design, strength, and affordability of our mounts are second to none.

Engine placement in these Jeeps should consider the following points:

  • Left-right offset location is similar to factory at ~1-1/4" to the driver's side
  • Avoid installing the engine too low (axle clearance and other issues)
  • Avoid installing the engine too high (transmission tunnel interference, etc.)
  • Set your engine to 4-7 degrees of tilt rearwards, like the factory engine & powertrain
  • It is usually best that Chevy and Gen III+ V8 engines install approximately 3" further forward, using the back of the engine block face as the datum
  • When mocking up your engine installation location, pay special attention to radiator and fan clearance.
  • Firewall modifications are not expected.

Since TJ Jeeps have higher hood clearance, clearance for classic Small Block and high Vortec (truck style) intakes and accessories is not a problem. However, XJ / MJ Jeeps have low hoods and will require the use of lower car intakes and accessory packages.

Novak Gen III+ engine mounts for TJ, XJ, & '76-'86 CJs will remove any guesswork from the engine installation location as they are predetermined for the best location and engine clearance margins.


Driveshaft length changes may be required. Chevy engines (with their rear distributors) can install around 3" further forward than AMC engines. It is also recommended that LS family engines be installed 3" further forward than the factory block (using the back face of the block as the datum point) for exhaust clearance, firewall access, etc.

Because of the engine placement and transfer case SYE kits are frequently installed with many of these conversions, you may end up with a longer rear driveshaft (very desirable for lifted Jeeps) and a shorter front driveshaft.

Some installers, concerned about the expense of new or modified driveshafts, attempt to let the existing driveshafts dictate engine, transmission and transfer case location, often to the detriment of the project. Our recommendation is to prioritize the correct position of drivetrain components over saving a few dollars which is usually regretted in the long run with compromised positioning.

Jeeps that require extensive travel or specialty-built driveshafts have this option available through several fabricators across the nation. These are normally specified after placement of the new transmission and measured at vehicle ride height. As the rear driveline gets shorter, it is often advantageous to us a Double Cardan or “CV style” rear shaft with the correct geometry at the axle to minimize vibrations and possible binding.


Use of factory axles is completely acceptable with this conversion. Axle upgrades are not necessary, but they may be chosen for reasons external to this transmission upgrade.

Also See