Overview
The Alloy USA high strength rear 30 spline axle shaft, part 21128, is the rear passenger side shaft for a Dana 44 with 30 splines. It fits the 1999–2004 Jeep Grand Cherokee (WJ). It is not for use with a Hydralok differential.
Alloy USA makes the shaft from 4140 grade steel. It is heat treated and induction hardened and is up to 40% stronger than stock. Its cold spline rolling produces splines that are stronger than cut splines, and the shaft carries a 10-year warranty.
Key features
- Rear passenger side shaft
- 30 splines
- 4140 grade steel, heat treated and induction hardened
- Cold spline rolled, per Alloy USA
- Not for use with a Hydralok differential
- Backed by a 10-year warranty, per Alloy USA
Choosing and fitting an axle shaft
A rear axle shaft carries drive torque from the differential to the wheel, so its strength matters most when the vehicle is under load on rough trails. Shafts usually fail at the splines or near the flange, often after a hard landing or a locked-differential turn. Before buying, check that the differential behind the shaft is a standard open or locking unit that matches this shaft’s spline count and Dana 44 housing.
When the old shaft is out, look at the bearing seats, the spline wear on the differential side gear and any cracks at the hub flange. A worn side gear can chew through a new shaft quickly, so inspect it before you reassemble. Replacing the bearings and seals at the same time keeps the axle job to one teardown.
Specifications
| Brand | Alloy USA |
|---|---|
| Part number | 21128 |
| UPC | 804314192501 |
| Axle type | Dana 44 |
| Axle location | Rear |
| Side | Passenger side |
| Spline count | 30 splines |
| Material | 4140 grade steel |
| Spline process | Cold spline rolled |
| Not for use with | Hydralok differential |
| Warranty | 10 years, per Alloy USA |
Vehicle fitment
It fits the 1999–2004 Jeep Grand Cherokee (WJ) across its trims.
Other Grand Cherokee generations, including the ZJ, are not in this list. Confirm your vehicle’s year, model and trim before ordering.
Installation notes
Check the rear carrier before installing, since this shaft is not for use with a Hydralok differential.
What’s included
A single rear shaft for the passenger side.
