AX15 Input Shaft 10 Spline 1992-Up, Motive Gear AX15-16A

A Jeep AX15 that whines in every gear except fourth, grinds a tooth pattern you can hear with the clutch out, or has a pilot tip chewed up by a dry bushing usually needs a new input shaft. This Motive Gear AX15-16A is the 10-spline input shaft for 1992-and-later AX15 five-speeds, the version with the larger .750 in. pilot tip, used behind the 4.0L in Wrangler YJ and TJ, Cherokee XJ and Comanche MJ.

What the input shaft does in an AX15

The input shaft, also called the main drive gear, is the front gear of the transmission. The clutch disc slides on its 1-1/8 in. 10-spline section, the front bearing carries it in the case, and the drive gear on its back end is in constant mesh with the countershaft. Every gear except fourth sends power through that mesh. In fourth the synchronizer locks the input directly to the mainshaft for the 1.00 ratio, which is why a damaged drive gear goes quiet in fourth. The mainshaft nose rides on needle bearings inside the pocket at the rear of the shaft, and the pilot tip at the front rides in the bushing or bearing in the crankshaft.

Symptoms of a worn AX15 input shaft

• Whine or howl in first, second, third and fifth that disappears in fourth, from a pitted or chipped drive gear
• Growl in neutral with the clutch engaged that stops when the pedal goes down, often the input bearing pressed on the shaft
• Fourth gear popping out under load, from worn engagement teeth on the drive gear or a tired fourth-gear blocking ring
• Clutch chatter or a disc that hangs up on worn or notched splines
• A scored or blued pilot tip, or a squeal at the pilot when the pedal is pressed

How to confirm before you buy

Check the oil first. Low or wrong lube makes an AX15 noisy and notchy, and Jeep specifies 75W-90 GL-3. Then listen: a noise that changes with clutch pedal position is in the front of the box, while a noise that grows with road speed in every gear is further back. Once the case is apart, inspect the drive gear teeth, the dog teeth for fourth, the splines and the pilot tip. If the shaft is fine and you only need bearings and rings, the AX15 master overhaul kit is the better buy. If the pedal sinks or the clutch drags, check the hydraulics first; a YJ clutch master and slave cylinder costs far less than a teardown. Our guide to manual transmission repair cost explains what a rebuild involves.

Fitment

Every AX15 uses a 1-1/8 in. 10-spline input, so the spline count does not separate early from late shafts. The pilot tip does: 1992-up shafts use a .750 in. tip, while the 1989-1991 units had a smaller tip of about .59 in., and the crank bushing or bearing is sized to match. This AX15-16A is the 1992-up version. Jeep also changed the input bearing retainer and pilot bushing when the clutch slave moved outside the bellhousing in the mid-1990s, so compare the new shaft with your old one side by side: pilot tip diameter, overall length, spline count and drive gear tooth count. If your Jeep has a mixed engine and transmission, measure the pilot tip and the crank bore. Send us your year and VIN if you want help. More rebuild parts are in our rebuild kits category.

Install notes

• The shaft comes out after the front bearing retainer is removed and the case is split. Press the input bearing off the old shaft and fit a new bearing to the new one; reusing a noisy bearing defeats the repair.
• Install new needle bearings in the shaft pocket, a new fourth-gear blocking ring and a new front retainer seal. Jeep lists a 0.6-1.6 mm gap between the blocking ring and gear cone as the wear limit.
• Replace the crank pilot bushing or bearing with one sized for the .750 in. tip. A Lisle pilot bushing remover pulls the old one without pulling the engine apart.
• Use a clutch disc with a 1-1/8 in. 10-spline hub, and check that the disc slides freely on the new splines before the transmission goes in.
• Refill with 75W-90 GL-3 gear oil. Jeep lists about 3.10 liters for 4WD and 3.15 liters for 2WD, filled to the bottom of the fill hole.

How do I tell an early AX15 input shaft from a 1992-up shaft?

Measure the pilot tip. The 1992-up shaft, like this AX15-16A, has a .750 in. tip. The 1989-1991 shafts had a smaller tip of about .59 in. Both have a 1-1/8 in. 10-spline clutch section.

Does this fit my Jeep Wrangler TJ or Cherokee XJ?

It is the 1992-up AX15 shaft used behind the 4.0L in Wrangler YJ and TJ, Cherokee XJ and Comanche MJ. Compare it side by side with your old shaft for tip size, length and tooth count, or send us your year and VIN.

What else should I replace with the input shaft?

The input bearing, the needle bearings in the shaft pocket, the fourth-gear blocking ring, the front retainer seal and the crank pilot bushing. If the box has many miles, a master overhaul kit covers the bearings, seals and rings.

Why does my AX15 only whine in some gears?

Fourth is direct, so the input drive gear is not loaded against the countershaft. A whine in every gear except fourth points to the input drive gear or countershaft gear teeth.

What oil does the AX15 take?

Jeep specifies 75W-90 API GL-3 gear lubricant, about 3.10 liters in 4WD models and 3.15 liters in 2WD, filled to the bottom of the fill plug hole.

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