Len vw

All I know is it’s a 12 speed

Hello, I’m working on an 85 Mack dump truck with the speedometer not working. Everything works well all the way back to the transmission tailshaft housing, so I pulled the tailshaft housing off and noticed the spiral gear around the tailshaft is not in an area that the pencil gear will line up with it. The gear doesn’t seem to slide at all, so could there be a wrong part in here somewhere, or is it possible that something was installed backwards? Not sure what to do here.