Adapting the

GM 6L80E & 6L90E Transmission

to the

Jeep Models 231, 242, 249 Transfer Cases

Novak's 6L80E & 6L90E transmissions 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.

Product & Features


Bearing Input:

use the options above to select the correct product for your conversion

6L81cad

Advanced computer modeling methods were integral to the design of our 6L81 adapter assembly. We were able to push the bounds of product and process well beyond the status quo.

***Please note, with the exception of transmission length and output spline count/diameter all of the information provided below applies to both the 6L80E and 6L90E transmissions***

The Adapter

The Novak 6L80 to Jeep NP / NVG transfer cases adapter is compact at only 3-1/4" long for a combined transmission and adapter length of 26-1/2” for the 6L80E and 27-3/4” for the 6L90E (equivalent to a ~19-1/2” or 20-3/4” manual transmission). The adapter itself is machined of a 6061T6 billet aluminum alloy, featuring thick flanges and a heavy cross-section.

Transfer Case Clocking & Rotation Options 

Our adapter is drilled for multiple clocking locations from near-factory (20 degrees down) to near-flat (3 degrees down). However, pan clearances and front axle width may inhibit the flatter options.

Rear Mount Provision 

This transfer case adapter's design is based on Novak's Universal Series adapters that feature a modular mounting and support system. Included with the adapter kit is a steel base that is a highly configurable mounting foot, and is ready to accept our industry standard urethane isolator mount and is available for purchase below.

Contents

Billet adapter housing, transfer case input gear, transfer case to adapter gasket, fastening hardware, steel mounting base, and instructions.

Applications & Compatibility

Transmissions

There are two versions of the 6L80E transmission output shaft that will work with the Novak adapter. The stock 4WD version will work without modification to the transmission. The stock 2wd truck version will work with several modifications done externally. Other versions require the output shaft of the transmission be replaced and the rear of the unit sealed. All years of the 6L80E are compatible with the kits. More specific information on the modifications needed is provided below.

The 4wd version 6L80 is ready to bolt up to our 6L81 adapter kit. Disassembly of the transmission is unnecessary as the 32 spline 4wd style output shaft which protrudes about 3" from the rear face of the 4L80E transmission main case is correct for this kit version. Disassembly of the transfer case is necessary to install a new matching 32 spline input gear.

The input gear installation is a 2-3 hour bench job and usually includes either a simple gasket and seal replacement or preferably a full rebuild of a tired transfer case, especially a chain replacement. It is not requisite that you rebuild your transfer case to successfully complete the conversion. However, it is certainly worth consideration especially if your transfer case leaks or has many years of service. You will be going all the way into the front of the transfer case to install in the input gear. Our superior quality New Process master rebuild kits along with a top quality chain are the perfect solution for the job and, available below.

Early vs Late Input Gear Style

231_input_long_wide231_input_long_narrow 

The NP/NVG input gears are divided early and late about 1993-1994. However there are no guarantees that things are original or that the 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 above 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 special case requiring special gears. It is a late cut with additional machining required.

NP & NVG Transfer Cases 

ss231_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.

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

  • 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) is longer than 2.2". These will require shortening with a cut-off saw and/or lathe and finished with edge breaking chamfers

***Because the 6L81 kit requires the replacement of the input gear on the transfer case, it is NOT compatible with the 241OR transfer case. However, because of the impressive gear ratio combination of the 6L80E vs the other options available, the 241OR transfer case 4:1 low range is really not necessary especially when one considers the added torque of the V8 in front of it.***

Jeeps

Because this is a longer transmission, more so on the 6L90, it is not compatible with most short wheelbase Jeeps if they have much lift, due to driveshaft angles. CJ7 and similar length Jeeps may be feasible if the lift is mild. However, CJ8 Scrambler Jeeps, other longer Jeeps, especially the full sized trucks and Wagoneers are ideal candidates if punishing transmission duty is a prime consideration.

Engines

Because of the complex nature of the communication between engine and transmission on these transmissions we recommend that the native engine be used with its matched transmission. The 6L series transmissions have an internal TCM (transmission control module) and take a signal via the can bus along with other inputs to calculate the best shifts and control. These units use clutch to clutch shifting on all but one of the forward gears and are extremely exact in their control. See our knowledge page linked below for more information.

While possible, separate control of the 6L series transmissions is a complicated proposition and not something for which we provide support.

Related Products

Transmission Rear Mount

This transfer case adapter's design is based on Novak's Universal Series adapters that feature a modular mounting and support system. Included with the adapter kit is a steel base that is a highly configurable mounting foot, and is ready to accept our 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.

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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. More information can be found here…

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The 6L80E & 6L90E require a special fitting at the transmission to use the braided lines


6L80E & 6L90E 2WD Seal Kit

Any of the 2WD transmissions need to be sealed up with the following kit that includes the rear seal and necessary plugs. The output will also need to be cut as specified in the instructions to the 4WD length.


 

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.

Block_TransTunnelCover

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.

Block_SK2XC
Block_SK3XR
Block_SK2XZ
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Block_K101
Block_K100






 

Transmission Shifters for the TH350

Your TH350 will require a shifter assembly to work properly. If equipped with an automatic shifter on the column and you would like to keep that method of shifting, we recommend this kit:

Block_ACA-1804

We also offer two cable shifter kits that work well. This will be best determined by your personal preference depending on the Jeep it is going in, certain shifters work better. We have special brackets for the TJ to accept a special shifter version in the console. Other quality shifters made for the TH350 will also work well. We have found that the cable versions are usually easier to install and position correctly.

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New Process Rebuild Kits 

The New Process (or later New Venture Gear) transfer cases are unusually strong for their mass and size. As long as your chain isn’t stretched and you keep up with fluid levels they will take a surprising amount of power and abuse. Like anything else, time and use takes its toll and these rebuild kits consist of the best available components including top quality chains and bearings. The rebuild process is not overly difficult, and if you are there anyway to put in an input gear, our advice is to rebuild, especially considering that the chains can stretch with use.

The 231 kits are divided early and late about 1993-1994. However there are no guarantees that things are original or that the 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. Early uses a 24mm wide bearing and late is 16mm wide.

Block_231MR-1


The Rubicon 241OR rebuild kit is available here.


The 242 kits are a little more pragmatic with chain use. Most of the light Jeep models are the same but there are some variations in those that used a V8 as well as the Liberty and AMG versions. These kits are offered as rebuild components and the chains separately. The same guidance applies to year breaks as the 231 for the rebuild kits. Chains are model and style specific.

Block_242MR-1


Chains for the 242 had 2 pitch sizes, 2 joint styles and 2 widths and all in different combinations. 

new_process_chain

Chain Style


Use the above illustration in the event you are not certain about the provenance of your NP242 transfer case chain joint type.
 

This is the most common chain used in the XJ and other light duty Jeeps.


The WJ Grand Cherokee and Dodge V8 applications commonly used this wider chain.


The Liberty is a unique animal with this version and rebuild kits vary as well.


Some Jeep XJ & ZJ (Europe), NP242ECE models used this chain.


The H1 AMG HMMWV, Humvee, Hummer version is 1-1/4” wide and the coarse pitch.


Installation Requirements

Tools

The New Process transfer case requires hand tools, large snap ring pliers and RTV to reseal. Rebuilds are a little more involved but not much.

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.

Clocking Information & Driveshaft 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 Drivers Drop

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 right, (passengers’s side in the USA) away from the front differential in a Wrangler or similar application. This gives the best balance of weight (and more importantly clearance) for the driveshaft going to the front axle. Clearance is usually quite good in these applications; both the steering and front driveshaft push things towards 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.

Driveshafts

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 of our customers, fearful at the perceived expense of new or modified driveshafts, attempt to let the existing driveshafts dictate engine, transmission and transfer case location, usually to the detriment of the project. Our recommendation is to always value the correct position of drivetrain components over saving a few dollars which is usually regretted in the long run with compromised positioning. Sometimes the application allows use of the existing shafts without modification. While that is perfectly acceptable, it should not be the first priority. 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. Novak can also accommodate your needs on this if provided with dimensions for the shafts at a reasonable rate.

Axles

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