Adapting AMC I6 & V8 Engines

to the

AX15 & NV3550 Transmissions

The AX15 has become a popular retrofit transmission into a variety of Jeeps featuring the AMC 232, 258, 304, 360 and 401 engines. Because it features the same front bolt pattern as the AX15 the NV3550 is also a conversion option for these engines and installs similarly as described below.

Product & Features

This swap can be performed using mostly stock parts; however there are a few key areas that the Novak pieces really do become essential. Your best and strongest results will be to use our parts exclusively throughout but we will cover all the options.

Use of the 1994-1999 AX15 or the new Novak-supplied AX15 is recommended over earlier AX15's due to the requirement for the proper front bearing retainer. In those early applications a new retainer can be purchased to make these 1988-1993 AX15's compatible when they are available, as they are getting harder to source. With these particular transmissions you might consider the alternative swap using our AMAX15 kit which, in many ways due to clutch actuation, is a better way to go.

The two main components to this swap are the correct transmission and bellhousing which follow directly. But on this particular conversion the saying “the devil is in the details” is an accurate portrayal.

AX15 Transmission

These are brand new units from Aisin and are stronger than any of the original Jeep or Dodge pieces. Originally rated as a Light Duty unit, these carry a Medium Duty rating. They have been successfully used behind LS1, LS2 and the like. With proper care they are extremely strong. Included is our exclusive straight stick that may be bent to the perfect ergonomic location for your application.



All AMC engines from 1972-2006 featured a compatible bellhousing bolt pattern. This AX15 / NV3550 bellhousing produced for the 4.0L in Jeeps from 1994-2006 will work across this array of AMC I6 and V8 engines. It has the favorable and required external hydraulic slave cylinder provision over its previous design with the problematic internal concentric hydraulic release bearing system. While it is sporadically available new, we offer a good used version that has been media blasted and inspected for functional use. These bellhousings come as a kit with pivot ball, arm, and retention spring.


Applications & Compatibility


The following transmissions will work with this procedure: 

  • 1994-1999 AX15 or the new Novak-supplied AX15 
  • NV3550 installs similarly as described below.
  • 1988-1993 AX15 with a new 1994-1999 style retainer

Be aware there are different rotations on the transfer case between Wrangler and XJ applications. The new AX15 we sell is the Wrangler rotation but can be machined for XJ positioning on request (no charge). Two wheel drive versions work the same as 4x4 versions on engine side of the installation procedure described here but if you want to attach a transfer case, then the entire rear half, output shaft, and several other pieces must be changed to allow the transfer case to bolt up. These extra steps usually make this impractical.


This procedure is compatible with all 1972-2006 AMC 232, 258, 4.0L, 304, 360, and 401 engines. There are some variations between versions but all can be made to work with the right combination of parts. Late 2004-2006 4.0L engines use a different pattern CPS that is not in the correct location for this bellhousing. This would also be a good application to consider the alternative swap using our AMAX15 kit which is a better way to go in many ways due to clutch actuation and machining being required to accommodate the CPS for those years. 

The flywheel should be native to the engine, particularly on the V8s as they are externally balanced. We have seen varying height flywheels which is one of the reasons our adjustable clutch release components are usually essential.


Because of its assembled length, CJ7 or longer wheelbases are compatible. Anything shorter simply leaves insufficient rear driveshaft length. Full sized Jeeps, Wagoneers and Cherokees are good candidates, especially for the stronger Novak transmission version. Just keep in mind the rating of the transmission and you’ll be fine with those applications.

Related Products

Pilot Bushing

One of the following Pilot Bushings is required for all installations. Please choose your applicable engine and transmission combination.

Transmission Rear Mount

The AX15 and NV3550 feature a threaded base for support and isolation of the transmission and transfer case. Factory style isolator mounts are difficult to work with in any situation other than as a direct factory replacement. Novak has engineered a universal style rear mount that is easy to affix to a variety of Jeep crossmembers and is very strong and highly adjustable. We recommend it in any retrofit situation. More info on this mount can be seen here.


Clutch Kit

This popular clutch assembly from 1980-1986 Jeeps is our preferred kit for holding power yet reasonable pedal pressure. The disc's spline hub features the correct 1-1/8" x 10 spline configuration for these transmissions.


The disc can be purchased separately for those early applications natively using the 10 spline 1-1/16” disc.


Adjustable release bearing

While sometimes not needed in this application, it is priceless when clearances dictate its use. With all the variabilities in flywheel and clutch height, we adamantly recommend its use. Further information is here.


Hydraulic Clutch Actuation

If your Jeep has the master cylinder, that part can be reused. If not, we would recommend this master for most Jeep applications.


The Novak adjustable slave cylinder offers several advantages over stock plastic slave pieces:

  • Billet 6061T6 hard anodized construction
  • Rebuildable, not a disposable part
  • Conventional double flare fittings allowing either our braided stainless line or standard hard line use rather than an integrated plastic failure-prone line
  • Adjustability - which is severely lacking in the stock piece



Adapting the Dana 300 to the AX15 & NV3550 Transmissions

Transfer Case Adapter

Novak's #153 adapter kit is recommended for joining the AX15 & NV3550 to the popular Dana transfer case as found in 1980-1986 Jeeps. The AX15 can be adapted to the Jeep Dana 20 transfer case using:


Novak's #152 adapter kit. *Warning* Watch closely the overall length of the 152 combination.


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.


Transfer Case Shifter Kits

Many of these transmission retrofits end up in earlier Jeeps and they often require a modified transfer case shifter kit. For the Jeep Dana 300, we recommend the Adjustable Length twin stick kit with these transmissions. The TX300 can be used but is positioned further back and requires modification to the shifters, pan, and tub to clear.


Later Jeeps will likely want to look at our cable shifter line here.

Installation Requirements

With the parts specified above, this is generally a bolt together procedure using normal mechanics tools. A few applications will require minor cutting or drilling but all products come with instructions for their installation. This is a fairly straightforward swap. 


Transmission placement is largely determined by factory engine location. It is not necessary in typical conversions to change the engine position. Setting the powertrain to the proper factory or conversion pitch angle - usually tilted down ~5 degrees (3-7 acceptable) is recommended.

Engines & Engine Mounting

Later 4.0L inline 6 engines are not all the same on mounting location. If you are swapping early to late, or late to early and the engine involves a Grand Cherokee, check carefully that the mount locations are the same.

If converting to a V8 in conjunction with this upgrade, aftermarket engine mounts are available to ease its installation.


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.


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.

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