Adapting the GM 4L60-E (later version) Transmission

to the

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

Adapting the 4L60E to Jeep New Process transfer cases

Kit 4L61-23, adapting late GM 4L60E, 4L65, 4L70 transmissions to Jeep NP 207, 231, 241, 241OR, 242 & 249 transfer cases w/23 spline input

Kit contains:

  • Adapter housing
  • Transmission output shaft, 23 spline
  • Reluctor ring, pressed on to shaft
  • Vehicle Speed Sensor, GM version
  • Seal
  • Seal spacer (works with both long and short input gears)
  • Transfer case to adapter gasket
  • Transmission to adapter sealing ring
  • Fastening hardware
  • Modular steel mounting base
  • Instructions

Our 4L60-E (including the 4L65 & 4L70) to the Jeep New Process (or New Venture) transfer cases conversion makes for one of the most refined assemblies both on-road and off-road. This kit has become our most popular transmission to transfer case combinations.

The Novak 4L60E to Jeep NP231J transfer case adapter is compact at only 3.0" long for a combined transmission and adapter length of 25.5" (equivalent to a 17.5" manual transmission). The adapter itself is machined from 6061-T6 aluminum, featuring thick flanges, a heavy cross-section, and superior strength.

The new 23 spline 4L60E output shaft is machined from 300M alloy steel which provides a substantial strength upgrade even over the stock 4L70E version. The new Novak shaft splines directly into the OEM style input gear of an NP transfer case. This requires disassembly of the transmission, and we recommend the services of a transmission professional.

Only a 23 spline version is available. If your NP231 has a 21 spline gear (if you're replacing the AX5 manual transmission), we recommend replacing the input gear with one listed below. An in-depth discussion about New Process input gears can be found here.

4L60E, 4L65E, 4L70E transmission assembly

Applications & Compatibility

Compatible Transmissions

The 4L61 adapter is compatible with all versions (2wd or 4wd) and years of the 4L60E, 4L65E & 4L70E transmission. We’ll refer to all these as 4L60E in this page but compatibility is all the same. For differences in these variations refer to this page. There are no inherent advantages to the 2wd vs. 4wd transmission as the factory output shaft will be replaced with the new Novak version.

These kits are for the hexagonal six-bolt rear pattern case made starting in 1996 and include a detachable bellhousing. Some 1999 and earlier versions have a four-bolt rear pattern and non-removable bellhousing. See our Kit #171-E if this describes your transmission.

The basic adapter installation is a 1.5-2 hour bench job and will include at least simple gasket and seal replacements. This is a good time for a more thorough master rebuild and update of the transmission. Many consider one of our complete Novak remanufactured and upgraded transmission packages. The advantage of a superior, professionally built transmission, tested, delivered and ready to bolt in.

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 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 strong transmissions native to 1/2 ton truck, SUV and sports car applications. Full Size Jeeps such as Wagoneers, J-Trucks, etc. are conversion candidates for them. There are numerous upgrades available for the 4L60E should stock strength come into question.

Compatible Engines

Any engine that can be made to work with the 4L60E 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.

There were also a lot of other combinations available to the 4L60E that may not be perfect candidates for a Jeep swap. The Atlas series inline engines, 3.8L in the 90’s era Camaro, a rear configuration for the Corvette, there is even a bellhousing available in Australia for the Holden that will allow a High Feature DOHC V6 to mate to the 4L60E. Sometimes just because it’s possible doesn’t make it a good idea, but we’ll leave that part up to you.

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.

Be careful when working with a Gen IV version of a 4L60E transmission. They feature a special Transmission Control Module that is very picky about the engine and it's controller. We recommend sticking with the matched Gen III style 4L60E transmission control systems.

Lastly, be aware of Gen III engine crank spacing, 4L60E flexplates, 4L60E bellhousing depths, 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.

Related Products

Urethane Rear Mount for Crossmember
Transfer Case Input Gear, 23 Spline
Transfer Case Input Gear, 23 Spline
NP207 Input Gear 23 Spline
Auto transmission cooler
1976-1986 Jeep floor tunnel cover
Slip Yoke Eliminator for NP231 Transfer Cases
TurnKey 4L60E 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.

Strength Comparison of 27 vs 23 Spline Versions

The 27 and 23 spline shaft sizes are quite comparable in minor diameter (the diameter of the shaft at the root of the splines) and therefore, strength. Diameters are very close and the finer 27 spline vs the coarser 23 spline has shown no significant strength variation. The 300M material used in production of the Novak shaft is of a superior strength both in PSI yield and torsional resistance - which is exactly the type of load these shafts see. Aside from that, fundamental design strengths are comparable.

GM 27 spline and Jeep / Dodge 23 spline shafts have a history of great strength in factory applications and Jeep aftermarket set-ups.

Output Shaft Strength

broken automatic output shaftWe’re avoiding the problem of a broken shaft like this one by going through the trouble and expense of making our output shafts from a solid bar of exceptionally strong 300M alloy steel, instead of lower grade alloys or friction welding salvage GM shafts. A second, sometimes less obvious but pernicious problem is the issue of warpage during friction welding and heat treating - which cannot be corrected when the shaft journals are already ground and worn at or below factory specifications. Novak shafts receive a final grind of bearing journals after the heat treat process to ensure the ultimate finish. The Novak shaft is produced to factory specifications with stress risers removed. Our 4-axis CNC cut of spiral gear, oil feed passages and other features are no small tasks. This attention to detail, maximized strength through design and material along with precise tolerances provide the ultimate parts for your project.

Also See