If it's a C clip type axle (like a Dana 35) some play is normal (1/2 inch is way too much). It's common for them to have maybe 1/16 inch or so. If it's the type of axle that relies on the press fit of the wheel bearing to hold it together (like a Dana 44) there should be very little play, if any. There should be no vertical play on either type. Best of luck - John