Identifying the series of GM 12 bolt rear end...?
 

I've searched and tried to watch some youtube but am still trying to figure out how to identify what series of 12 bolt rear end I'm looking at. Found one for a decent deal somewhat local but... guy thinks is out of a GTO (which if I understand correct makes it a series 3) but also thinks it has 4.55 gearing (which would have to be a series 4 right)? How do guys actually know what series they are looking at.

I've got a 69 Beaumont with a 454 so I'm thinking I want 3.73 gearing (has to be a series 3 right?)...

So confused. Ha!

I am not sure if these are 10 or 12 bolts but this is how you tell. And your right finding this information is like a trade secret. https://i.postimg.cc/Njmb5qyd/carrier.jpg

That is amazing. Thank you. Any chance you know what a 4 series would look like in comparison to these?

Nope I looked a long time for one. All we know is it isn't these 2.

Https://ibb.co/3R4bY8D

*wont let me imbed the photo for some reason*

So I finally got mine and pulled it apart. Gearing is a 4.56 so I'm assuming this makes it a 4 series. If my measurements are correct, its 1.82 from the flange to the end of the bearing.

It clearly has a large shim on the flange... to allow it to take a series three gear set I assume... although it brings it to about 2.02... which seems to be a hit heavy. My measurements might not be perfect though as I'm eyeballing that one.

Call richomnd gears tech dept. They were very helpful with my van.