I was reading some information on line and came across this great post on Model A Rear ends and the use of a brass subber to help the ring gear from walking away from the pinion..causing rear end desintegration.
Here are a couple of photos to show where a snubber is located. I use a Kiwi Quickchange center section. This rear is using a Halibrand manual from speedway that showed a snubber in the later V8 quickchanges. Vic King " Midnite Oil " he said they had put a snubber in the rear end on their dragster to keep the ring gear from pushing away from the pinion, this being the weak spot on the "A"rear end. The one is made out of bronze and give it less than .005 clearance. When the ring gear pushes away the pinion will try to climb the ring gear and break the casting. This is where most model "A" halibrands will show traces of welding