741 8 3/4

Unless you disassemble it for inspection the only other way I know of is to stick axles in both sides and lock one in a vise and put a pry bar on the other and try to turn it backwards. This is the way I have done it before. It should be pretty hard to turn. If it spins easily it's worn out.

Also if you can make sure and get a clutch type unit since they're rebuildable. Here's a link to a page that shows what the 2 look like

http://www.moparts.org/Tech/Archive/axle/13.html