Aisin-Warner AX15 Transmission
The Aisin-Warner AX15 transmission is a very successful, medium-duty, standard shift, five-speed transmission. It was introduced in the 1988 (mid-year) YJ Wrangler and XJ / MJ Cherokee / Comanche Jeeps, and found in 1989*-1999 Jeep XJ, YJ, and TJ models. Its only year in the ZJ Grand Cherokee was 1993, and only with the six-cylinder.
The AX15 is found behind the AMC 258 and the Mopar 4.0L (242 ci) I6 engine. The AX15 is also found in Dakota trucks and is closely related to the Toyota R154 as found in the Supra Turbo, though the case rear halves and gear ratios vary. It is also related to (or referred to) as the AN5, AR5, MA5 in GM and Isuzu applications.
The AX15 was available in Jeeps in both 2wd (typ. XJ / MJ applications) and 4wd versions.
*The AX15 was a mid-year upgrade from the weak Peugeot BA10/5, installed in Jeeps built after March 9, 1989.
The AX15 is a split-case, top shifting, overdrive transmission with the shifter being located in the rear section of the transmission. The AX15 is fully synchronized in all gears. All gears are helically cut.
Gear ratios for the AX15 are: 3.83, 2.33, 1.44, 1.00, 0.79, for first through fifth, respectively.
The 4wd version of the AX15 transmission case is 16-1/2″ long. It features a cast aluminum case with a cast-aluminum mid-plate. The case is generously ribbed and features the shifter in the rear quarter of the assembly. In the vein of newer transmissions, the AX15 uses dowel pins for bellhousing alignment.
The 4wd version of the Jeep AX15 has a 23 spline output shaft for connecting to the transfer case input shaft. This shaft protrudes about 1/2″ past the rear face of the transmission.
The AX15 was used with an internal slave/throw out assembly up through the 1993 model year. In 1994, a more conventional slave cylinder and cross-arm were used. The input shaft is a 10 spline x 1-1/8″ and its stick out length is 7-1/2″.
1989 to 1991 AX15 input shafts have a smaller (~19/32″) pilot tip. 1992-1999 AX15’s have a larger (~3/4″) pilot tip.
The AX15 looks similar to the AX5 and they are occasionally confused in identification as well as interchange.
Marrying the AX15 to the NP207 transfer case as found in earlier YJ and XJ Jeeps requires that the 207’s longer input gear be shortened with a hard saw or lathe to 2.1″ of stickout length. This prevents bottoming of the input gear in the spline lead-outs of the AX15’s mainshaft.
The factory manuals call for 75W90 GL-3 gear oil for the AX15 transmission. This fluid is essentially obsolete; superseded by GL4, then GL5. However, many GL5 fluids have friction modifiers that are not compatible with synchronizers, so make sure to check for compatibility.
It is the experience of some that a 50W fluid provides quicker shifts and especially so in colder climates.
The AX15 is one of the good successes for Jeep transmissions. They are generally regarded as the best five-speed transmission ever installed into a Jeep.