USA Standard Master Overhaul Kit For Nissan Titan Rear Diff

If your Nissan Titan, Frontier 4WD, Xterra or Pathfinder has started to hum from the rear axle at highway speed, knocks when you take up driveline slack, or leaks gear oil past the pinion seal, the M226 rear differential needs new bearings. The USA Standard Gear ZK NM226 master overhaul kit covers that axle with one part number: every bearing, race, shim and seal for a full rebuild, plus the parts you need when you regear.

What the master overhaul kit does in the Nissan M226

The M226 is the Dana 44-based rear axle Nissan used under its full-size and mid-size trucks, with a 12-bolt rear cover. Inside, a pair of tapered pinion bearings carry the drive load and a crush sleeve sets their preload. The differential carrier turns on two side bearings, and the shims beside them position the ring gear for backlash and bearing load. A separate shim sets pinion depth. When those bearings wear, the ring and pinion stop meshing where they were set up, so the axle gets loud first and starts chewing up gears later.

USA Standard lists the ZK NM226 contents as carrier bearings and races, pinion bearings and races, a pinion seal, a complete shim kit, ring gear bolts, a pinion nut, a crush sleeve, oil baffles and slingers, thread locker, marking compound with a brush, silicone and a gasket. The bearings and races are Koyo. Having the baffles, slingers and a cover gasket in the box means you are not reusing tired small parts on a truck that is apart anyway.

Symptoms of a failing M226 rear

• Whine or howl between roughly 40 and 70 mph that changes when you lift off the throttle
• A growl that gets louder with a trailer or a loaded bed
• A clunk on throttle tip-in or when shifting into drive or reverse
• Play you can feel when you rock the pinion flange up and down
• A wet pinion seal or oil thrown on the inside of the frame
• Bearing flakes stuck to the drain plug magnet

How to confirm before ordering

Drive the truck on a smooth road and note when the sound appears: on acceleration, on coast, or both. Our guide on carrier bearing noise describes how a worn side bearing sounds compared with a pinion bearing, and bad transmission vs bad differential noise helps if you are not sure which end of the driveline it is. Then check for flange play, drain the oil, and pull the cover. Recording backlash with a dial indicator before teardown gives you a starting point.

Fitment

USA Standard lists the ZK NM226 for the M226 rear with the 12-bolt cover in these trucks: 2004-2014 Nissan Titan 2WD and 4WD, 2003-2014 Frontier 4WD, 2003-2012 Pathfinder 2WD and 4WD, and 2003-2014 Xterra 4WD. Nissan did not put the M226 under every Frontier, Xterra or Pathfinder; many have a smaller rear axle, so count the cover bolts and check the axle tag before you buy. The pinion spline changed for 2008 (29 splines on 2004-2007 Titans, 24 on 2008 and later), which affects the flange, not this kit. Still unsure? Send us your year and VIN and we will confirm. If you prefer Timken bearings, the Yukon YK NM226 kit covers the same axle.

Install notes

• Yukon's setup chart for the M226 lists pinion bearing preload at 15-25 in-lb with new bearings and 0.006-0.011 in backlash on 5-cut gears. Check preload with an inch-pound torque wrench as you tighten the pinion nut.
• Fit the new oil baffles and slingers in the same positions as the old ones; they protect the pinion bearings from oil starvation and debris.
• Keep the bearing caps in their original sides and orientation.
• If the flange is grooved where the seal rides, replace it. For 2004-2007 trucks there is the 29-spline YY NM226-RND-29 flange; 2008 and later trucks need the 24-spline version.
• Regearing a 2008 or later Titan for bigger tires? Set up the new gears with this kit, for example the Yukon 3.13 ring and pinion for the 2008-up M226, and match the front ratio.
• Install the cover with the gasket or silicone, fill with the gear oil and limited-slip additive your owner manual calls for, and break in new gears gently.

Does the ZK NM226 fit a 2012 Frontier?

Only if that Frontier has the M226 rear. USA Standard lists the kit for 2008-2014 Frontier 4WD with the M226 and 12-bolt cover. Many Frontiers have a smaller rear axle, so check the cover bolt count and axle tag first.

What comes in the kit?

Carrier and pinion bearings and races, pinion seal, complete shim kit, ring gear bolts, pinion nut, crush sleeve, oil baffles and slingers, thread locker, marking compound with brush, silicone and a gasket.

How is this different from the Yukon YK NM226?

Both fit the M226 rear. This USA Standard kit uses Koyo bearings and adds oil baffles, slingers and a gasket. The Yukon kit uses Timken bearings.

Is the ring and pinion included?

No. This is the installation and bearing kit. Gear sets in the ratio you want are sold separately, and this kit has everything needed to set them up.

Will a new pinion seal alone stop my leak?

Only if the pinion bearings are still tight. If the flange has play or the axle whines, the worn bearings let the flange wobble and a new seal will soon leak again.