Adapting

Chevrolet & GM Standard Shift Engine Bellhousings

to the

Jeep AX15 Transmissions

Jeep AX15 adapter kit to GM Bellhousings

Kit GMAX15, adapting the AX15 transmission to GM bellhousings

This conversion kit joins the popular AX15 overdrive transmission to the standard GM pattern bellhousings for a variety of OEM transmissions. This affordable and straightforward method allows the installer to retain the bellhousing they already own, and in many cases, the existing clutch and its release system.

The adapter is precision designed and expertly CNC machined from alloy aluminum. Its thick cross-section provides ample thread engagement and high structural integrity. Precision indexing is achieved through locating dowels to the transmission and bearing retainer to the bellhousing. This adapter is 1" thick for a total adapted length of 17.7".

The adapter installs onto these transmissions with no change of input gear or other transmission internals. Cutting the transmission input shaft is not required as the adapter spaces the transmission properly for the GM crank and clutch assembly. A new pilot bushing is required for this assembly. See Related Products below for the one matching your particular GM engine.

Kit Contents

Included are the adapter plate, bearing retainer (which serves as a centering index for the GM bellhousing and clutch release bearing sleeve) and required hardware.

Applications & Compatibility

Compatible Jeeps

This engine conversion is compatible with TJ & LJ Wrangler Jeeps in which this transmission was native. It is also compatible with CJ7 and longer Jeeps in which builder may be retrofitting this transmission. CJ5 Jeeps do not have a long enough wheelbase for the longer, five-speed transmissions.

These are strong transmissions, and full Size Jeeps such as Wagoneers, J-Trucks, etc. are conversion candidates for them unless used for more aggressive driving or heavy work situations.

Compatible Engines

Nearly all GM Generation I-III engines are compatible with this conversion, including Chevrolet Small Blocks, Gen III+ V8's, Chevrolet V6's and Chevrolet I6 engines. Also, Buick, Olds, Pontiac, and other GM engines are compatible with this adapter assembly if you have a standard shift classic GM bellhousing and flywheel for your engine. Even some of the front wheel drive and unique engines could be made to work with this adapter using certain factory or aftermarket bellhousings sharing this common bellhousing / transmission bolt pattern.

Compatible GM Bellhousings

Chevrolet Muncie Saginaw Bellhousings

The classic Chevrolet bellhousing, with the four-bolt rear pattern. Buick, Olds, Pontiac and other bellhousings with the same rear face are equally compatible.

your GM bellhousings will typically feature either a 4-11/16" rear face bore or a 5-1/8" rear face bore, the latter typically only from Chevy / GM trucks from 1968-1991. Our adapter will works natively with the smaller bore bellhousing and with the larger bore bellhousing if you choose the 5-1/8" press-on spacer ring. If you are unsure of your bellhousing bore, buy the ring and return it after your build if it turns out you don't require it. See Related Products, below.

Clutch Assembly

Because of the 1-1/8" x 10 spline configuration of these transmissions, use an off-the-shelf GM clutch kit (pressure plate & disc) with this conversion.

Be aware of the following clutch configurations - see Related Products below for more information:

  • 153 tooth classic flywheels typically use a 10-1/2" clutch assembly
  • 168 tooth classic flywheels typically use a 11" or 12" clutch assembly
  • Gen III+ engines should use a taller aftermarket flywheel that normalizes the clutch kit to a classic 168 tooth style

The pilot bushing included with most clutch kits will not be compatible with the pilot tip diameter of these transmissions. See Related Products below to select your proper pilot bushing.

Clutch Release

The factory style master cylinder can be retained. The hydraulic line and slave cylinder need to be changed over to a system which is compatible with the GM bellhousing. Novak's #HCR Series slave cylinder kits are ideal for this situation. We also provide a hydraulic line and brass fitting which allows the conversion from the factory hose. See Related Products, below.

Clutch release bearings need to be a GM compatible unit. Because of the various heights of pressure plate fingers, consider Novak's adjustable throwout bearing assembly, available in Related Products, below.

For more theory and in-depth discussion about clutch systems, see Novak's Guide to Clutches, Linkages and Bellhousings.

Related Products


Jeep T14 to GM pilot bushing
GM engine to AX15 transmission pilot bushing
GM Gen III Engines to Jeep Pilot Bushing
Adjustable clutch release throwout bearing
Hydraulic release master kit for Jeeps
Hydraulic release master kit for Jeeps
Adjustable clutch arm pivot
GM LS Vortec Bellhousing
GM Chevy Bellhousing
Extended depth flywheel for GM engines
Bolts for GM engine flywheel to crank
GM clutch kit
GM clutch kit
GM clutch kit
AX15 & NV3550 Rear Mount
Adapting NV3550 transmissions to Jeep Dana 300 transfer cases
Adapting NV3550 transmissions to Jeep Dana 18 & 20 transfer cases

Installation Requirements

AX15 joined to a Chevy / LS bellhousing, complete with #HCR clutch release assembly, #RMAX rear mount and #153 ring for a customer's Dana 300 transfer case.

Tools

A drill, 33/64” bit, and various smaller bits are required, in addition to typical mechanic's hand tools.

Placement

Transmission placement is largely determined by 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

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 featuring the AX15 & NV3550 transmissions have higher hood clearance, clearance for classic Small Block and high Vortec (truck style) intakes and accessories is not a problem. Same for CJ's and Trucks that are getting these transmission / engine combos as retrofits. 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.

Driveshafts

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.

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