[gto4evr]

Hello, more of a curiosity here but does anyone know why there are two different seals listed for the rear ends between 66-69 and 70-72? (we're talking about the 8.2 10 bolt BOP A body rear ends). I was struggling with all the various suppliers on seals and part numbers to application years being all over the place as I was looking to get a seal for my 71 Lemans, so I started back at the beginning.

the 72 master book lists: 9793685 for 66-69 A bodies and then 404294 for the 70-72.

I decided to just track down NOS since I can't trust any of these cross reference charts I found.

I bought both since I've got some pre-70 cars too and wanted one on the shelf.

So, parts came in. I can't see a difference in the measurements with a set of calipers. other than the 404 being painted and the 685 being plain, I can not figure out what makes them different. I've got no good way of measuring the inner rubber for shaft diameter but that has to be the only possible difference. but, when I gently touch the edges with the calipers, they seem to be the same as well.

I was expecting to see some national oil seal numbers or something stamped into these but they're actually stamped with the GM part number on the inside metal so that pushes the aftermarket interchanges back into the sweeping generalizations they make when things are close enough so one size fits all kind of thing which I don't trust.

any master rear end tech's out there that know of some little nuance here I'm missing!?