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

to the

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

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.

Product & Features


The Adapter

The Novak 4L60E to Jeep NP231J transfer case adapter is very 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 billet 6061 T6 aluminum, featuring thick flanges, a heavy cross-section, and superior strength.


Advanced computer modeling methods were integral to the design and manufacture of our #4L61 adapter assembly. We were able to push the bounds of product and process well beyond the status quo.

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 for purchase below.


Kit contains billet adapter housing, transfer case input, transfer case input spacer with seal, transfer case to adapter gasket, transmission to adapter sealing ring, fastening hardware, steel mounting base, and instructions.

Applications & Compatibility


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 from now on but compatibility is all the same. For differences in these variations refer to our knowledge page linked below. There are no inherent advantages to the 2wd vs. 4wd transmission as the output shaft will be replaced. 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 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 five-speed manual transmission), we recommend replacing the input gear with one listed below. 

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.


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_advance_adapters_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.


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 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. 


Any engine that can be made to work with the 4L60E will work with this adapter. All of the above mentioned native engines along with others that can be adapted via a front adapter (such as our 437 series kits) open up numerous possibilities. 

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 stray 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 have reverse, third and max line pressure, probably not the best solution for a Jeep.

Related Products

Transmission Rear Mount

This transfer case adapter's design has a structural base for an industry standard urethane isolator mount, available for purchase. This is our preferred rear mount unit. Our kits are designed for it, and its usage is essential to protect powertrain components from the flex and movement typical of any automobile, but especially Jeeps.

Whether you are assembling onto a stock crossmember/skidplate or if you are setting up a high-clearance skid plate, you will find it to be a clean and simple process.



Transmission Tunnel Cover

Because the transmission and transfer case shifters are often in a different location than factory in these Jeeps, this new transmission tunnel cover gives the installer a clean slate. There are no screw holes nor transmission & transfer case shifter holes, allowing the installer to drill and cut them as necessary. An easy way to get a perfect fit is to use the old cover as a template, making cuts as necessary, then overlay on the new aluminum piece for perfect holes.

The finish is natural brushed aluminum, which looks pretty terrific, but it can easily be primed and painted to suit, if desired.

This tunnel cover is compatible only with 1976-1986 CJ Jeeps.


New Process Transfer Case Shifter Options 

Often the shifters are linked to your old transmission, body, or both. As things move or even just to have a better setup these shifter solutions prove invaluable and extremely popular.


Transmission Cooling

Transmission Cooling is critical to the life of all automatic transmissions. Conventional in the radiator tank coolers are simply not adequate for long life on a Jeep’s transmission. Here are the products we recommend for best performance and ease of installation.



23 Spline Input Gears

If you have a 21 spline input transfer case, our recommendation is to replace the input gear with a 23 spline version. The NP/NVG input gears are divided early and late about 1993-1994. However there are no guarantees that the transfer case is original or that the gear change was made as a clean break 93 down and 94 up. 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 photos show the differences in width of the bearing location and the stepped shoulder between the bearing and the gear. 23 spline input gears are available to replace the anemic 21 spline found in all too many applications. Please select the appropriate gear below.


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 tools. Transmission side will be 10mm studs or bolts and the transfer case side is 3/8” fasteners.


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.

Engines & Engine Mounting

mmtj-g3If converting to a V8 in conjunction with this upgrade, aftermarket engine mounts are available to ease its installation. Because of the broad spectrum of engines and vehicle combinations used with this adapter, it would be difficult to list them all here. Whatever your application, Novak likely has the perfect solution. From a 225 Buick V6 in a CJ2A to an LS3 in your JK, we’ve got you covered. 

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

Engine Placement

Engine placement in these applications is an effort in compromise to find the best position overall as a package. Generally the engine will be about 1” or even more towards the left, (driver’s side in the USA) away from the front differential in a CJ application. This gives the best balance of weight and more importantly clearance for the driveshaft going to the front axle. Your tight spots will be steering to exhaust on the left (hold that as tight as you can) and clearance for the front driveshaft on the right. Fore and aft position will vary with the Jeep model and engine. Have a CJ5 and Gen I with a rear distributor? You’ll be better off a little forward for more rear driveshaft length and clearance for that HEI. If you are in a longer Jeep and using an LS engine with no distributor, you’ll have more fan clearance and better balance if you hold it to the rear. Usually for ground clearance tuck things up nicely for height to avoid damage to oil pans and other life giving parts in the Jeep. Common sense and taking a step back to look at things overall goes a long way.


Driveshaft length changes are often required. Most conversions to these transmissions will require that the rear driveshaft be modified to be shorter and front driveshaft longer.

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.

Driveshaft modifications and rebalancing can be affordable when performed by driveline, RV or tractor implement specialists. New driveshafts are an option, but not necessarily a requirement in regards to the actual successful conversion if your existing driveshafts are in good condition.

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