[GordonJ]

To Dudley's comment - having purchased axles for Ford for nearly 5 years, the standard process for North American axle manufacturers today (and probably for many, many years prior) is to machine the ring and pinion independently, bring them together and run them through a lapping operation. This an abrasive slurry that flows over the gearset, removing inperfections and "mating" the two components together - highs to lows and lows to highs. From that point forward, the set needs to remain together. This would explain scribed or stamped numbers on the individual components if they were a replacement set. In normal assembly plant operations, the sets are packaged together such that they are picked and assembled together.

For those who care, the other method of making axle gearsets is to machine and grind. This process is most often found in European axles. In this process, the gears are machined first and then put into a grinding machine to finish the gear lands. The action is so precise that the individual components do not need to be mated and can be picked independently for assembly into the axle. Why aren't all axles made this way? Many, many reasons. Primary reasons are Grinding is a little more expensive and grinding leaves what some have described as a "harder" gearset. This really has nothing to do with material hardness, but more of a feel or sound of the gearset. The ground gears are described as harder and potentially louder because of the precise fit of the gears as they lock together and the lapped gears are described as softer and quieter because the gears tend to flow into each other since they are less perfect but mated together. Design Engineers tend to feel strongly about one approach or the other but the only real difference I ever saw was that ground gears were used in performance applications while lapped gears were used in everyday vehicles. Another interesting sidenote told to me by a gear design consultant was that ground gears can sometimes be so precise that if not properly designed, they can act like a bell in operation - like striking tuned metal with a metal hammer.

Enough axle trivia...