Inside the 21/2-ton Rockwell
Centersection: Double reduction-style - The upper ring-and-pinion gearset drives an intermediate gear that, in turn, drives the big, gnarly bull gear. The differential or locker is housed inside the carrier sandwiching the bull gear.
Upper ring-and-pinion: 22-teeth on ring gear, 9-teeth on pinion = 2.44:1 Lower bull gear and intermediate gear: 33-teeth on bull gear, 12-teeth on intermediate gear = 2.75:1
Final gear ratio: 6.72:1 (combination of 2.44 ring-and-pinion and 2.75 lower gear)
Axleshaft: 1.62-inch, 16-spline
Differential: Open four-spider gear design or Detroit Locker (PN 225S-15)
Bolt pattern: 6-on-8 3/4
If it's still there, the easiest way to identify which style front axle you've found is by the tag (arrow). If the tag says Timken, then it's an older undesirable model with either the Bendix- or Rezepa-type shaft. If the tag says Rockwell, then it's got Spicer-type shafts. | 
If the tag is gone (and chances are it will be), then just cut the knuckle boot and peek inside to see if it has Spicer-style shafts. Boyce Equipment carries new boots for $28 each, and almost all of the old ones are hashed anyway. |
If you're not looking for a rebuilt axle, then just grab the driveshaft flange and check it for slop. Most experts tell us that the bearings on the upper pinion shaft are the most common wear item. The rest of the axle is pretty much bombproof. | |