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.
For clarity, consider that there are two available tracks in converting AX15 & NV3550 to AMC engines:
- Using a 1976-1986 T150, T18, T176, T4, SR4, T5 style bellhousing + a Novak #AMAX15 adapter
- Using a 1994+ 4.0L to AX15 / NV3550 bellhousing - this method described below
Compatible Jeeps
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.
Compatible Engines
This procedure is compatible with all 1972-2006 AMC 232, 258, 4.0L, 304, 360, and 401 engines. If using a 2005-2006 4.0L engine, you will need its bellhousing with the Crank Position Sensor (CKP) at the 2 o'clock position as viewed from behind the engine.
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 essential.
Components Required
This swap can be performed using mostly stock parts; however there are a few key areas that the Novak pieces really are important.
- Transmission
- AX15, 1994-1999 version (This is the style of the new AX15's provided by Novak - see below)
- AX15, 1989-1993 version, if you replace the early front bearing retainer with the later version, available below
- NV3550, 2000-2004
- Retainer, front input bearing, 1994-1999 AX15 #4636382. See Related Products, below
- Bellhousing, 1994-2004 Jeep 4.0L, #52107552. See Related Products, below
- Pilot bushing. Details below
- Adjutable release bearing, Novak #TB3. This telescoping release bearing reaches the pressure plates on the lower profile flywheels seen on classic AMC I6 and V8 engines. See Related Products, below
- Clutch master cylinder. your factory Jeep one (if equipped) will likely work. We recommend the 1987-1990 YJ style as it is easy to work with
- Clutch slave cylinder. The factory one can often work - its pushrod will need to be cut and rounded and clutch adjustment must be optimal. However, we recommend the Novak #HCR-S34A as it has more travel and adjustability. Read more below...
Adjustable Billet Slave Cylinder
The Novak adjustable slave cylinder offers several advantages over stock plastic slave pieces:
- Billet 6061-T6 & hard anodized construction
- Rebuildable, not a disposable part - see associated rebuild kit
- 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
- 10% more travel than the factory AX15 slave cylinder
- Comes with billet spacer, adjustable pushrod and match plate
Kit HCR-S34A, slave cylinder assembly, ¾” version to AX15, NV3550, NSG370 bellhousings
Kit HCRK-34, rebuild for Novak ¾” hydraulic slave cylinders
Transfer Case Adapters
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 is recommended for joining the AX15 to the Dana 18 & 20 transfer cases. However, this combination is too long for any Jeep shorter than a CJ7.
AX15 Clocking & Tailhousing Considerations
Be aware there are different rotations AX15 4wd adapter between Wrangler and XJ applications, the latter being clocked down 10 degrees to clear the steeper tunnel in the Cherokee. If installing an XJ AX15 in a YJ or TJ, you will want to redrill the tailhousing or send it to us for this service.
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.
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.
Placement
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 I6 engines are not all the same on block boss mounting locations. 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.
Recommended & Related Products
AX15 Transmission
These are brand new units from Aisin and one of the greatest Jeep transmissions ever. They have been successfully used behind AMC, GM and Ford V8 power. Included is our exclusive straight stick that may be bent to the beset ergonomic location for your application. Read more about this transmission package.
Transfer Case Shifter Kits
Many of these transmission retrofits end up in earlier Jeeps and some conversions benefit from an aftermarket shifter kit. For the Jeep Dana 300, the factory shifter works fine when using the #153 Novak adapter above. But we can also recommend the twin stick kit.
Later Jeeps have great shifter options as well. See the full line-up here.
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.