To a certain point, there is no way to be 100% sure that the axle you're buying is not going to fail. Most salvage yards offer a short term warranty. That's not going to help much if you have to drive back to Tulsa if you have a problem. However, there are certain 'clues' you can pick up by doing a simple inspection at the yard. First, salvage yards now list the Model Year of the axle as well as the approximate Mileage on the truck at the time it reached the yard. When I was shopping for my axles, I tried to locate something with less than 100K miles. The lower the better but something with really low miles might be more expensive to purchase. On site, I popped both covers to inspect the ring and pinion gears. Look for chipped, cracked or broken teeth, which would indicate abuse, poor initial installation or previous work. I skip those axles. Also, spin the axles by the rotors and watch the differential operate. Everything should operate smoothly (not 'notchy'). Gear oil is not the best smelling but should not smell burned either. Most likely it will be a very dark green color, almost black. Look for leaks, too. Gear oil will 'creep' over a wide area (one drop may eventally cover a 6" x 6" area, if not more) and collects dirt like a magnet. So, what may appear to be a nasty leak could really be something easy to fix. Since I replace axle seals regardless, I concentrate on the pinion gear seal which is a little more difficult to replace. If everything looks good, it probably is. It's pretty cheap to replace internal carrier bearings and seals. As for the axles shafts, if there's no indication of other problems, they should be good as well.
