There should be a retaining bolt that is holding the shaft in the center of the differential. Remove that bolt and the shaft should come out. When you get the shaft out you need to push in on the axle (with the wheel and brake drum removed). Then you can remove the c clip from the end of the axle and the axle will slide out.
This might help. http://www.thirdgen.org/techboard/tr...ing-axles.html