Jeep AX15 5-Speed Manual Transmission Bearing & Synchro Kit

This is the USA Standard Gear ZMBK163JWS bearing kit for the Aisin AX15 five-speed manual, the aluminum-case box used behind the Jeep 4.0L inline six. It fits the Wrangler YJ and TJ, Cherokee and Grand Cherokee XJ/ZJ, and Comanche MJ from the late 1980s through 1999, and the same core kit covers the AX15 that Dodge ran in the Dakota. If your transmission is apart on the bench, this is the set of bearings and synchro rings you drop back in.

The kit includes the input bearing (92mm outer diameter), the rear mainshaft bearing (72mm outer diameter), the countershaft and rear countershaft bearings, single-piece brass synchronizer rings, wire-type synchro springs, and the case and shaft seals. These are the parts that wear out an AX15: a growl or whine that changes with which gear you are in points to a spun or pitted bearing, and a crunch going into second or third under a quick shift is a worn synchro ring letting the gear clash before it locks.

Use it during a full teardown. Press the old bearings off the input shaft, mainshaft, and countershaft, pull the synchro rings off each hub, and clean and inspect the gears and shafts before you reassemble. Set input and mainshaft bearing preload with the correct shims, seat the new synchro rings on their cones, and check ring-to-gear clearance with a feeler gauge before the case halves go back together. Replacing the whole bearing and synchro set at once is the only way to get the noise and hard shifting out for good rather than chasing one worn part at a time.

This is a hard-parts bearing and synchro kit, not a gear set. Broken or chipped gears, worn shift forks, and a scored input shaft are inspected and sourced separately. Confirm you have the AX15 (not the AX5 or the later NV3550) before ordering, since the bearing sizes and synchro rings differ between those Jeep five-speeds.