Thank you LEE T, finally someone who can answer a simple question without being a smart ass!!
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I'm of the belief that the later design ('61? and later thru '64) are of a heavier construction, and thus should weigh more if that's true... Did you have weights for both the original design and the update design?
If you are asking me, then the answer is no, I only have the weight of the exact one that markm asked for.
Rocky, I was speaking of the differential chunk *housing* castings, and I'm totally not sure there was a change in the Posi chunk housing casting number... or not?? I've been trying to figure that out as I have a '61 dated and '63 dated '812' P-casting posi carriers...
My understanding of the thicker vs thinner gears has to do with the ratio...
With all the rear ends I am used to looking at that do not use spacers, when the pinion gets fewer teeth and smaller,the ring gear gets thicker. Back in the 90s when I bought 9 inch Ford junk on a daily basis I could just about guess the ratio by looking at ring gear at a distance. I never dealt in many early Chevy jugs but I am sure same applies.
55-56 3rd member housings were a bit lighter than later models. But I doubt if the difference is more than 1/2 pound.
55-56 ring gears are thinner than later models. When they first designed these axles, they didn't build in accomodations for 3.36 or 3.08 gears. With the bigger pinions on these gears, they had to make all the other gears thicker, and move the ring gear mounting surface on the differential case. 57-up gears and differential cases allow the 3.08 and 3.36 gears.
Also, the castings for 62-63 Chevy II axles are the same basic design, but are quite light relative to the others.
The difference between a p-case and an open case is a rib that's there on the open case which had to be removed for clearance with the posi differential. I don't think they are heavier at all. The rib can be removed to allow you to put a posi differential in an open 3rd member housing.
I don't think there's any significant difference in weight among all this stuff except for the Chevy II 3rd members. Even with that one it's only slight.