Driveline vibration out of now where! Help!

Side note: if you are going to remove the Speedo Gear to take a look at the Large Tail Shaft Bearing, take and mark the speedo gear aluminum flange (where the speedometer cable screws on) to the tail shaft housing with a dry marker. this way you you can get it back in the correct spot to go with the plastic gear that is inside.
ok, but how will i be able to check that bearing just by looking through the hole without being able to grab hold of it and spin it and feel for roughness?