As Dog described, but also take any old screwdriver and hold the shaft in at the center of the impeller, as you're pulling the impeller out. That way you won't pull the shaft out. My impeller on my former A4, as well as on my current diesel, had a circlip (circle clip) on the shaft holding the impeller in place. I never saw much function to the clip as the cover holds the impeller in place.
1983 Ericson 33
Channel Islands, California