AX15 5-Speed Transmission Master Overhaul Kit Jeep

A Jeep AX15 that grinds going into second or third, whines with the clutch released, or drips gear oil from the bellhousing is telling you the synchronizer blocking rings, bearings and seals are worn out. Crown Automotive's AX15MASKIT is the master overhaul kit for the Aisin AX15 five-speed in the 1988-1995 Wrangler YJ, 1997-1999 Wrangler TJ, 1988-1999 Cherokee XJ, 1988-1992 Comanche MJ and 1993 Grand Cherokee ZJ. Crown lists it as including the bearings, seals, shifter gasket, blocking rings, small parts and RTV, so the consumable parts of a teardown come in one box.

What the overhaul kit does in an AX15

The AX15 is a five-speed synchromesh manual with an integral shift mechanism in the shift tower of the adapter housing. Jeep's service manual lists ratios of 3.83 first, 2.33 second, 1.44 third, 1.00 fourth, 0.79 overdrive fifth and 4.22 reverse. Every forward gear is engaged through a brass blocking ring that has to match the speed of the gear to the shaft before the sleeve slides over. When those rings wear, the friction cone can no longer synchronize the gear and you get clash. The input, output and countershaft bearings carry the gear stack, and the front bearing retainer seal, rear seal and case sealer keep the oil in. This kit replaces all of those wear items while the case is apart.

Symptoms that point to an AX15 overhaul

• Grinding when shifting into a forward gear, worst when cold or on fast shifts, from worn blocking rings
• Whine or growl in neutral with the clutch engaged that goes away when the pedal is pressed, typical of a worn input or countershaft bearing
• Noise in every gear that grows with speed, from output shaft bearing wear
• Gear oil dripping from the clutch housing, which Jeep traces to the front bearing retainer or its seal
• Leaks at the case joints or tailhousing seal

How to confirm before you buy

Rule out the cheap causes first. Jeep's manual points out that hard shifting is often low or wrong lubricant, or a clutch that is not fully releasing. Check the oil level at the fill plug on the driver side, with the vehicle level; it should be at the bottom edge of the hole or no more than 1/4 inch below it. Then confirm the clutch hydraulics are releasing fully. A sinking pedal or a slave that leaks is a hydraulic problem, and a pre-bled assembly such as our YJ clutch master and slave cylinder or the TJ clutch hydraulic kit fixes it for far less than an overhaul. If the oil is correct, the clutch releases, and the grinding or bearing noise is still there, the transmission needs to come apart. Our guide to automatic vs. manual transmission repair cost explains what a manual rebuild involves.

Fitment

Crown lists AX15MASKIT for the AX15 in the Wrangler TJ 1997-1999, Wrangler YJ 1988-1995, Cherokee XJ 1988-1999, Comanche MJ 1988-1992 and Grand Cherokee ZJ 1993. Wranglers built from 2000 on use a different five-speed, and four-cylinder Jeeps of this era used the smaller AX5, so confirm the transmission before ordering. Jeep stamps the AX15 identification code on the bottom of the gear case. The input shaft changed during production too, which matters if you are replacing gears and not just consumables; our AX15 10-spline input shaft is for 1992-up units. Send us your year and VIN if you want fitment checked. Other kits are in our rebuild kits category.

Install notes

• Before teardown, measure gear thrust clearances. Jeep's specs are 0.10-0.40 mm for output shaft first gear and 0.10-0.30 mm for second and third; out-of-spec gears or thrust parts must be replaced, since the kit does not include gears.
• Check every blocking ring and the shift forks even though new rings are supplied. The manual specifies 0.6-1.6 mm between ring and gear cone, and replacing a fork whose hub clearance exceeds 1.0 mm.
• Lubricate components with gear oil as they go together and use petroleum jelly on seal lips, as Jeep instructs.
• Seal the case joints with the RTV in the kit; Jeep notes that gaps in the sealer, wrong bolt torque or non-recommended sealer are what cause leaks at the mating surfaces.
• Refill with 75W-90 API GL-3 gear lubricant. Jeep lists about 3.10 liters (3.27 quarts) for 4WD and 3.15 liters (3.32 quarts) for 2WD, then check the level at the fill plug.

New blocking rings can feel slightly notchy for the first miles; Jeep notes this usually fades as the rings wear in.

Which Jeeps does the AX15MASKIT fit?

Crown lists the 1997-1999 Wrangler TJ, 1988-1995 Wrangler YJ, 1988-1999 Cherokee XJ, 1988-1992 Comanche MJ and 1993 Grand Cherokee ZJ, all with the AX15 five-speed. It does not fit the AX5 used with four-cylinder engines or the five-speed used in 2000-up Wranglers.

What does the kit include?

Crown describes it as bearings, seals, the shifter gasket, synchronizer blocking rings, small parts and RTV sealer. Gears, shafts, shift forks and the case are not included and should be inspected and replaced separately if worn.

What fluid does the AX15 take and how much?

Jeep specifies 75W-90 API GL-3 gear lubricant. Approximate dry fill is 3.10 liters (3.27 quarts) for 4WD and 3.15 liters (3.32 quarts) for 2WD. Fill to the bottom of the fill plug hole with the vehicle level.

My AX15 grinds into second. Do I need the whole kit?

Check the oil level and clutch release first, because both cause hard shifts. If those are good, a worn blocking ring is likely. Since the case must be split to reach it, most rebuilders replace all the bearings, rings and seals at once rather than just one ring.

Should I replace clutch parts at the same time?

With the transmission out, it is the right time to inspect the clutch, flywheel and hydraulics. A leaking slave or worn pressure plate can cause the same hard shifting you are trying to fix.

• Automatic vs. Manual Transmission Repair Cost: What to Actually Expect