Enter the beast
The AX15 manual transmission has always been an excellent gearbox that can withstand the torque and power of most V8s. The biggest problem now is the availability of new units.
Since there are no new NV3550 for replacements, we looked into the possibility of obtaining the Aisin Warner AX15 gearbox and using these as replacements instead and guess what? Succeeded.
Although the torque specifications of this gearbox are not mentioned in a maintenance manual, we consider it sufficient to be similar to the NV3550. The NV3550 was the gearbox that replaced the AX15, and Jeep used the same engine with the same vehicle classes.
The Aisin-Warner AX15 is a successful standard five-speed medium- and heavy-duty gearbox. It was introduced in 1988 (mid-year with the six-cylinder.
The AX15 is behind the AMC 258 and the Mopar 4.0L (242 ci) I6 engine. The AX15 is also found in Dakota trucks and is closely associated with the Toyota R154 as in Supra Turbo, although the rear halves of the gearbox and transmission are different. It also refers to (or is called) AN5, AR5, MA5 in GM and Isuzu applications.
The AX15 was available in Jeeps 2wd (XJ/MJ applications) and 4wd versions.
The AX15 is a split gearbox with a top gearbox, with a polar gearbox at the rear of the gearbox. The AX15 is fully synchronized in all gears. All gears are spiral cut.
The ratios for the AX15 are as follows: 3.83, 2.33, 1.44, 1.00, 0.79, first to fifth.
AX15 version 4×4 has a length of 16-1/2″. It has an aluminum die-cast body with a central plate made of die-cast aluminum. The gearbox is richly grooved and has a gearshift lever at the rear of the unit. According to the latest transmissions, the AX15 uses pins to align the cover housing.
The AX15 Jeep 4×4 version is equipped with an output shaft with 23 slots for connection to the input shaft of the transfer box. This shaft protrudes approximately 1/2″ beyond the rear wall of the gear unit.
The AX15 was used with an internal slave/exhaust device until 1993. In 1994, a more conventional cylinder and transverse arm were used. The input shaft is 10 welds x 1-1/8″ and the output length is 7-1/2″.
1988-1991 AX15 input shafts have a smaller pilot tip (~19/32″). 1992-1999 AX15 has a larger pilot tip (~3/4″).AX15 resembles AX5 and from time to time is confused in identification and replacement.
As the AX15 married the Jeep engines mentioned above, it is OEM compatible. It can also be adapted to the AMC I6 and V8 engines in the years 1972-1991 according to this procedure.
Individuals expect the AX5 to be replaced from time to time and assume that the AX15 will replace it directly. The bell and spline shaft housing patterns that count among these new similar gearboxes are fraudulently close, but not compatible.
AX15 adapted to the GM hood housing
In the factory manuals 75W90 GL-3 transmission oil is prescribed for the AX15 transmission. It is the experience of some that a 50W fluid provides for faster changes, especially in colder climates.
The AX15 is one of the good successes for Jeep transmissions. They are generally considered to be the best five-speed gearbox ever built into a Jeep. They are an excellent transmission and will continue to be produced by Aisin-Warner.