Auret,
I guess the best way to describe this is the amount of play or "slop" between the pinion shaft gear and the differential ring gear. It needs to be set properly for the gears to mesh as intended. That being said, I'm trying to figure out how to properly measure it and adjust on the type axle we have on the 113's. I think I understand how to do this on a differential that has bearing caps and adjusters and a back plate that allows access to an assembled rear, but the 113 axle pumpkin differs from these set ups in a number of regards. Wtch my posts to see how some of the experts suggest doing this. One of the great things about this site is that you can always find someone who is working/worked on the same issues.
Geogre Des