Adapting Chevrolet & GM Generation I-IV Engines

to the

Jeep AX15, NV3550 & NSG370 Transmissions

With the advent of quality five- and six-speed transmissions in Jeeps, we now offer the possibility of marrying them to various Chevy and GM engines in a straightforward and sanitary manner using our block-to-bellhousing style adapter assembly.

* Note: This kit has been discontinued.

Product & Features

Jeep adapter kit to GM engines

The Adapter

This plate style adapter is precision laser cut and machined. Precision CMM mapped and machined dowel locators and fastening points assure total concentricity for long transmission life. The adapter is plated in black zinc for corrosion resistance and appearance.


Both kits include the adapter, fastening hardware and instructions.


Pricing and product information to the right is shown for informational purposes. We recommend calling in and ordering this kit so we can tailor it for your exact transmission. Otherwise, make your order and we will follow up with you via e-mail or phone to verify your technical details.

Applications & Compatibility


This adapter is compatible with the:

  • AX15
  • NV3550
  • NSG370 - 4.0L I6 style, not 3.7L V6. It is possible, however quite expensive to retrofit the front half from a TJ NSG370 to the JK NSG370 and use the kit. Due to cost, our recommendation is to go with one of our HD AX15 transmissions instead as they are much stronger and have proven more effective overall. The GMAX15 would then be the best way to adapt to your engine.

This kit will work with either the earlier AX15 that uses the concentric, internal hydraulic throwout bearing, or the later style AX15 that uses the external slave cylinder.


gm_ls6_thumbThe following Chevrolet & GM engines are compatible:

  • 4.3L V6
  • Gen. I-II Small Block V8
  • Gen. III+ GM V8
  • Chevrolet I6
  • Chevrolet Big Block V8

***This list simply demonstrates what will bolt together and does not suggest that all engines are appropriate for the strength of all transmissions. These are light duty transmissions with the notable exception of our new AX15 linked above and which would be rated as a medium duty transmission. Power capability will depend on the condition of the transmission, vehicle weight, driving style, ability of the user and the base capacity of the transmission itself.

Pilot Bushing

Depending on the transmission you have and the engine you choose, your pilot bushing will vary. The appropriate bushings are available below and are required for installation.


For GM engines prior to the Gen. III & IV Series (LS & Vortec, 1997- present), you will use your GM / Chevrolet flywheel as per factory to your engine, which can be either the 153 tooth version or 168 tooth versions. The 153 tooth flywheel typically accepts the 10-1/2” clutch only and the 168 tooth an 11” or 12” clutch.

If you are using a GM Gen. III+ engine, we strongly recommend the use of our extended height LS / Vortec flywheel to normalize the clutch system. This model accepts both 11” and 12” clutches.


This conversion uses readily available clutch components based on GM pressure plates and their geometries. All of these transmissions use the 1-1/8” 10 spline input shaft. Choose the 10-1/2", 11" or 12" clutch according to your preference and flywheel compatibility. Jeep Wranglers are typically lighter vehicles and the smaller clutches are generally adequate and offer easy clutch pedal pressure. The larger clutches have more holding power and still have very reasonable pedal pressure when using the diaphragm style pressure plate. A more detailed discussion on this topic is available in Novak's Knowledge Base linked below. Clutch adjustment is also addressed in detail and reading this article is highly recommended.

Starter Motor

It may be required to clearance the starter pocket of AX15, NV3550 and NSG370 bellhousings to eliminate possible interference from the starter nosecone. A deburring tool is recommended (not a grinding wheel, for safety) or the installer can choose a small nosecone or no-nosecone version starter; common on modern gear drive starters.

Clutch Kit

Many common GM applications used the 10 spline 1-1/8” hub and as such, it is usually a matter of selecting the correct version. Three sizes are listed below. Most common is the 11” listed in the middle but all are serviceable depending on your needs. Generally the 10-1/2” is used on the smaller 153 tooth flywheel and is exclusive to that application. The 11” and 12” are usually interchangeable with large bellhousings and standard 168 tooth flywheels. Non-standard applications will need to watch for compatibility.

Also See