The Novak Guide to
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.
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. Otherwise, a new retainer can be purchased to make these 1988-1993 AX15's compatible, below.
Components Suggested, at a Glance
- Transmission, AX15 or NV3550
- Retainer, front input bearing, AX15 transmission, 1994-1999 - if using a 1988-1993 AX15 transmission, listed below
- Flywheel; native to the AMC engine being used
- Kit, clutch, diaphram, AMC I6 & V8 with 1-1/8" x 10 spline disc, ~11"
- Pilot bushing, two options, listed below
- Cylinder, master, clutch release, listed below
- Mount, rear, transmission to crossmember
- Transmission tunnel cover
- Transmission shifter boot
- Transfer case adapter, factory or aftermarket as applicable
- Transfer case shifter
- Bellhousing, 1993-2006 Jeep 4.0L to AX15 or NV3550 transmission
- Bearing, clutch release, throwout, Novak adjustable, AMC version
- Arm, clutch release, 1994-2004 AX15 & NV3550, external slave style, modifed for adjustable release bearing
- Kit HCR-S34A, slave cylinder assembly, Novak HCR style, 3/4" version
- Assembly, clutch line and flex hose, stainless and poly wrapped, 3/8-24 DOT 1/4 fittings
- Plate, shield, AMC engines to the AX15 bellhousing
- Clip, spring, clutch arm retention
- Pivot, clutch release ball
One of the best transmissions ever built for a Jeep is the AX15. They are available new, for purchase and with all the updates and improvements Aisin has learned from years of producing them.
Novak compliments these AX15's with our improved straight-stick shifter that is bendable by the installer (using heat at the bends) for their particular installation and optimum ergonomics.
More information on this AX15 transmission assembly can be found here.
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 and has the favorable and required external hydraulic slave cylinder provision over its previous design with the problematic internal concentric hydraulic release bearing system.
Mopar no longer makes nor stocks these bellhousings new; however, we do have several available in stock. Additionly, we offer a good used version that has been media blasted and inspected for functional use, contact us for availability.
|The clutch housing shield plate, installed.|
Bellhousing Cover Plate Kit
The variety of engine-to-bellhousing shield plates over the years are problematic for exchange on any other engine and transmission combinations than the factory ones for which they were intended. Novak manufactures this new, cleanly designed version of sheet aluminum that is thick enough to toughly perform its job, while maintaining the stackup tolerances of the bellhousing assembly.
Clutch Release System
This conversion requires a hydraulic clutch release system, and nearly every Jeep will benefit greatly from an upgrade to this if it doesn't already feature it. Use of a mechanical clutch would be contraindicated for a variety of reasons.
The heart of the success of any clutch release system is the throwout bearing. Our adjustable one is the ace up your sleeve.
Clutch Release Bearing
There is no combination of factory clutches and release bearings that will provide the right spacing and geometry for proper clutch release and operation for this conversion and the variety of clutch finger heights. Few bearing length options were available from the factory and even fewer of those are available on the market now. However, Novak's fully adjustable release bearing eliminates this problem and permits very fine adjustment for optimal clutch action.
More detailed information on this Jeep throwout bearing can be seen here.
Clutch Release Master Cylinder Kit
For AMC era CJ's and for YJ Jeeps, we recommend the use of this 7/8" diameter clutch master cylinder as found on CJ Jeeps from 1980-1986. This durable and simple master cylinder has standard DOT inverted flare fittings and is not difficult to install. Most Jeeps feature a firewall that is already marked for such a master cylinder, and whose pedal can be fitted with a boss for the pushrod. Some math and fabrication may be required for your application. TJ Jeeps may use their existing clutch master cylinder, or install a TJ master if needed.
Clutch Release Slave Cylinder
This setup uses a fully internal cross-arm release fork which has a different release ratio than earlier external forks. As such, we need to use a slave cylinder with slightly more linear travel than the master cylinder. For this, Novak's 3/4" slave cylinder assembly use in conjunction with the above 7/8" master is ideal. It features an adjustable pushrod, simple DOT inverted flare fittings and is supported by servicable replacement parts if ever necessary.
This overhead view shows the slave cylinder and line installed, routing nicely vertical before curving over the bellhousing and up the firewall.
Hydraulic Clutch Line
Our slave cylinder, above, uses a highly standard 1/4 DOT fitting. This is the female 3/8-24 threaded fitting ready for an SAE, male double-flare fitting. Most installers that have done any work with brake lines will be very familar with these, as will their local parts supplier.
For the easiest installation and the most professional look, we recommend our braided stainless steel and poly wrapped flex hose and line assembly (right). It features a flareless compression coupling that can accept the provided straight, 90 degree or 180 degree pre-bent lines. Or the installer can bend the provided straight line to best match their situation.
This line is ~3' in length.
For use with Novak and other hydraulic clutch master to slave applications with standard 3/8-24, DOT 1/4 fittings
Clutch Release Arm, Pivot & Spring Clip
Add the below three items which comprise the release arm and its necessary pieces. The release arm is modified with widened slots to work with the adjustable throwout bearing, above.
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.
If you are using the 1988-1991 AX15 with the ~15mm pilot tip, use this pilot bushing:
If you are using the 1992-2004 AX15 or NV3550 with the ~19mm pilot tip, use this pilot bushing:
Front Input Bearing Retainer
If you are using a 1988-1993 AX15, you'll need to replace the front retainer to upgrade to the external hydraulic release, as discussed above.
RMAX 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.
Some crossmember drilling is required and fastening hardware is provided.
Transmission Tunnel Cover
Because the AX15 & NV3550 shifters are biased more rearward than factory transmissions 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.
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 Currie style twin stick kit with these transmissions. See it here:
Transfer Case Adapters
Marrying these AX15 & 3550 transmissions to the Jeep Dana transfer cases is possible. See these pages: