i would be happy that the axle broke rather than the differential gears. there may be a weak link engineered into these to protect expensive components and labor. i had similar experiences with both Land Rover in the 1970's and Jeeps in the 80's. on the Rover the rear Half shaft would twist off before anything else was damaged and on the Jeep the hub was splined to the axle and the hub would strip before any real damage was done. "Collie will probably learn this some day"