does anyone know if all the differential oil comes out of the differential when the cover is taken off in an oil change?

 

All that matters, yes. No different than an engine oil change. There is always some residual oil that won't come out.

 

Yeah as jkeaton said, pretty much all comes out. I would try to get out as much as possible, not because I think the few ounces of leftover fluid are going to make any difference at all, but just to check thoroughly for any debris/metal shavings (small amount of metal "dust" is common and normal).

Also check and make sure your axle vent is not clogged just as a precaution. If it's the same as the 1st gens the vent is screwed into the driver's side axle tube and serves a dual duty of keeping the brake distribution block on.

 

is that axle vent inside where the differential is? on the drivers side?

 

Yeah, pretty much. Think of a bell laying on it's side and thats the diff. You can stick a rag in there to soak up any residual laying at the bottom, if you wish. I sprayed it all over with brake cleaner and let it dry out. There is a magnet sitting at the bottom that you should clean. Here is a pic of mine before I cleaned it.

 

It is on the differential housing. A vent with a tube that should run up to the frame rail.