If you want to choose the best used rear axle, there are several areas that you must examine. The condition of the lubrication oil in the center section is the best indicator to identify the best used rear axle for any application. The bearings must also be examined in order to assure that you have picked the best used rear axle. If choosing the complete assembly, you must identify the proper axle housing required to fit your specific vehicle; if choosing the axle only, you will want to make sure the bolt pattern is the same as the axle to be replaced. You may also wish to examine the axle splines to ensure they are of the proper count to fit your center section.
Axle housings can tell a lot about the axle that is located within. Any signs of accident damage, such as fire evidence or a visible bend, will mean that you should avoid that particular axle. Often, you can tell the bearing size of an axle by examining the axle housing, specifically, the axle tube ends. If possible, remove the center section or the rear axle cover to inspect the condition of the gear set and the carrier.
When attempting to secure an axle only, it is always best to buy a used rear axle that is installed in a complete axle assembly. Purchasing an axle that is in a pile of used axles or on a shelf can often lead to the purchase of a sub-standard used rear axle. When you find a complete axle housing, you can turn the axle and verify that it is in operable condition with no burned bearings or damaged splines.
If you wish to purchase the best used rear axle possible, never purchase an axle that has any signs of damage to either the axle flange or spline area. It is also best if the "new" used axle is complete with bearings, and when applicable, C-clips in place. When buying a C-clip-style axle, make sure to examine both the axle end as well as the C-clips themselves for any signs of damage such as overheating, scraping and rubbing damage. This can often indicate a worn or damaged bearing surface on the used rear axle.