The rugged Aisin AX15 5-speed manual transmission was a Jeep® and Dakota 4×4 mainstay from 1989 up. A later version of this transmission is now available new from Advance Adapters. Factory fresh, the unit is suited for both retrofits and OEM replacements. Many builders are attracted to the AX15’s reputation for reliable service and stamina.
Included in this how-to coverage are the steps to “clock” a YJ/TJ Wrangler AX15 for installation in a ZJ Grand Cherokee, an XJ Cherokee and some Dodge Dakota V6 4×4 pickups. The AX15 tailhousing adapter to the transfer case requires a 10-degree clocking change to fit these vehicles. Advance Adapters can provide a template for the new hole pattern.
Note: Be aware that this new AX15 transmission has the later 23-spline output shaft and a pilot/input nose of 0.750″ or approximately 19mm diameter. Early AX15 applications (to 1991) use a smaller diameter pilot nose (approximately 15mm or 19/32″ range, clearly smaller in diameter); some transfer cases (the NP207 in particular and older NP231 types) have a 21-spline input. A 23-spline input conversion gear is available for the NP207 or 231…The depth/length of the input gear is also a concern, and this impacts the fit between the AX15 output shaft and the transfer case input gear…Identify your transfer case type and measure the pilot bearing size before ordering this 1997-99 TJ Wrangler version of the AX15…Model year interchange, parts sizing, spline counts, transfer case input gear depth/length and the pilot size can each be solved with Advance Adapters parts. See the Advance Adapters catalog online or contact tech support.
The factory-new transmission available from Advance Adapters is a 1997-99 TJ Wrangler prototype that can be used as a replacement for 1987-99 six-cylinder Wrangler transmissions and the 2000-2004 TJ Wrangler NV3550 5-speed. For 1987-90 YJ Wrangler 4.2L models and the 4.0L YJ 4x4s through 1993, this prototype transmission also helps facilitate the upgrade/conversion to an external clutch slave cylinder. Either 1994-up factory parts or upgrade pieces available from Advance Adapters can complete this changeover.
Many builders are finding the AX15 transmission well suited for V8 transplants with reasonable horsepower limits. (300 would be the limit for a new AX15 transmission in my view; 275 would be better.) The AX15 is also a time honored retrofit and sensible upgrade for the light-duty AX5 equipped Jeep® vehicles. A new or properly rebuilt AX15 transmission is advisable for V8 conversions.
The vehicle depicted in this coverage is a 1998 XJ Cherokee two-door, factory equipped with an AX15 manual transmission and 4.0L engine. This Cherokee 4×4 came with an AX15 transmission that had the factory 23-degree clocking or tailhousing rotation. The new Aisin AX15 (TJ Wrangler type) has a factory 13-degree tailhousing rotation that must be changed.
AX15 tailhousings are factory drilled for a specific application. Fortunately, the flange of the tailhousing adapter is cast for drilling either tailhousing rotation. The YJ/TJ Wrangler AX15 versions came from Aisin with a 13-degree rotation. This new transmission needs a 23-degree rotation to fit the XJ Cherokee drivelines, body tunnel and transfer case shifter alignment. Advance Adapters can furnish a drilling template for moving the bolt pattern 10-degrees.
Advance Adapters’ Insights and AX15 Products
Advance Adapters has a list of products for installing, retrofitting and swapping the AX15 transmission. In addition to selling the ready to install 1997-99 TJ Wrangler prototype Aisin AX15 transmission assembly, a number of “kits” are available for installing an AX15 into other model year and vehicle applications. Here is the Advance Adapters approach to the AX15:
“The AX15 transmission has always been a great transmission able to handle the torque and horsepower of most V8s. The biggest problem now is the availability of new units. With the lack of availability of new NV3550s, we revisited the possibility of obtaining the Aisin Warner AX15 transmission and were successful. Although the torque specifications are not listed on this transmission in any service manual, we feel it’s similar enough to the NV3550. The NV3550 was the transmission that superseded the AX15; and Jeep used the same engine with the same vehicle ratings. With the availability of AX15 transmissions, we can now offer some additional transmission retrofit applications.
[Advance Adapters] NOTE: These AX15 transmissions feature a 13 degree tailhousing rotation and are exact replacement transmissions for 1997-2000 Jeep TJ Wranglers. If installing this AX15 into a Jeep XJ Cherokee, the tailhousing rotation will be wrong. Cherokee transmissions have a 23 degree rotation tailhousing. The rotation difference will lead to install issues with the Cherokee NP231 transfer case shifter. [This is our reason for redrilling the AX15’s rear adapter flange.]
AX15 Direct Replacement: AX15 transmissions were used between 1988 and 1999 in the Jeep vehicles. Since these Jeep vehicles are getting up in mileage, a new AX15 makes sense as a direct retrofit. AX15s were available in both an internal or external release bearing design. [The new crate AX15 is external slave type; this transmission can be fitted to an internal slave Jeep® by changing the front bearing retainer. However, most builders use this opportunity to convert the vehicle to an external slave. This does require a bellhousing and slave cylinder swap or conversion.]
Retrofitting the AX15 into an AX5 model: This is a newer kit for all 4-cylinder Jeeps 1987 to 2002. The AX5 is considered a light duty transmission compared to the AX15. Jeep vehicles equipped with larger tires and lower gears in the axle and transfer case may find the weak link in the drivetrain is the stock AX5 transmission. You can now install the AX15 in place of the AX5 to gain drivetrain strength. The good thing is that when you’re ready to replace the 4-cylinder with a larger V6 or V8, the AX15 is an ideal transmission for the power increase. See kits 712563 & 712564; this transmission swap will also require a new transfer case input gear with 23 splines if the original spline count is 21.
Peugeot 5 speed Replacement: The AX15 is the exact same length. The kits we offer include a new input gear for either the New Process 231 or 207 transfer case. (AX15 TO BA10 NP207 or NP231, Advance Adapters Part Numbers 27-3507AX15 and 27-3510AA.) Due to vehicle variances, some applications may require transfer case linkage modifications. Kits include a new bellhousing, transfer case shifter linkage, a crossmember adapter mount to retain the stock Peugeot rubber mount, slave cylinder kit, and an input gear for your transfer case.”
Advance Adapters offers individual and kit components for popular V8 conversions and installing an AX15 into Jeep® 4x4s originally equipped with other transmissions. This includes mate-up to the Dana 300, as the AX15 has become increasingly popular as a replacement for OEM transmissions in CJ 4x4s.
Note: For extreme use, high horsepower, heavier curb weight or a trailer hauler, the NV4500 remains the better swap option. NV4500 units have been used in vehicles like the Ram/Cummins and Duramax diesel trucks down to lightweight CJ Jeep 4×4 swaps. The AX15 is referred to by some as a “medium duty” transmission. This should not be confused with Medium-Duty Class truck stamina transmissions. The AX15 is not a “heavy-duty” unit like those found in a 3/4-ton or 1-ton Ram or GM diesel powered truck. Advance Adapters makes a variety of adapters to mate the NV4500 to Jeep® and other 4×4 applications. If you plan to place an exceptional load on the transmission, consider an NV4500 or equivalent transmission conversion.
The AX15 Rebuild Option
If you are considering a rebuild of your existing Aisin AX15 or a similar 150-series Toyota transmission, see the detailed step-by-step video and article at the magazine. This is complete how-to coverage of a rebuild: