I was told by a shop to replace the rear with a used axle from a junkyard as the cheapest way to go. Van is G-20, 1995.
Yes, let's use a used axle where we dont' know how many miles are on it, the condition of the bearings and how hard it was driven. Yes, excellent idea. As the bearings deteriorate the spatial relationship between the gears will change, moving outside the designed parameters. This will lead to increased wear on the gears as well as putting forces on the bearings (what's left of them) that will very quickly reduce their life even further. If the bearings explode you are looking at all the gears in the rear-end taking heavy damage and needing replacement; very expensive. If the bearings sieze, the rear-end will seize and lock up which means the tires will lockup. Could cause an accident, or worse.
That's going to be a minimum of a 9.5 rear end. The likelihood of failure of a used rear end is EXTREMELY low. If it's the 9.5, the only cause for any concern is the pinion bearing, which apparently had a few problems, but not nearly enough to condemn the entire lot. The 14 bolt full floating axle has been around since the 70's, if not longer, and the 9.5 (sometimes referred to as a 14 bolt semi-floater) has been around since 1982. Ask yourself how many GM trucks are running around from that vintage to give you an idea of how likely/common bearing failure is. :) What is the reason for the replacement suggestion? Axle bearings are a lot cheaper than replacing the whole axle, but even then failure is not common so why are you having to replace the whole thing?
If all you're doing is replacing the axle, then it should be easy. But, I don't understand why you wouldn't want to just replace the bearing. It's not that hard. Now, if you're talking about the carrier bearings, then that's another story. If you're looking at replacing the whole rear end, then look for one with low mileage and the same gear ratio. Again, if you're talking about the carrier gears, then the outcome of a bearing going out could be bad. At best, you ruin the ring and pinion; at worst, you lock up the rear end.
