I have had some difficulty finding where I can fill my 12 bolt. There is no plug on the cover, and the one hole that is threaded on top i believe is a break line mount. I have a 1968, however I believe the axle is from a later model because it has spring perches for the coils. thanks.

The fill plug is on the right side in front of the axle tube. Just above the web that runs along the side. It's about a 1/2npt pipe plug of there abouts.

Thank you Canted. It was right where you said it would be. I just had to scrape a little to see the plug. Its amazing what 20+ years of grease and grime can look like...

Now I am having difficulty finding which size my diff is. "both" of the gaskets at Advance Auto didn't fit. Does anyone know how I can check? I can get the serial #'s later if that helps.

????

Only one size 12 bolt passenger size rear for Chevys, there is a 12 bolt oldsmobile rear that has a 10 bolt ring gear though. There's also a 12 bolt truck rear, that's NOT the one you need.

I'm assuming you're talking about a 68 year model

I was told by somebody that the axle didn't have raised spring perches in 1968, which mine has. I have have been misslead on that. I believe I tried gaskets for 8.2 and 8.795 ring gear sizes, both for a 12 bolt. I'm considering cutting my own gasket pretty soon too.

8.2 and 8.5 size gaskets are 10 bolt

8.875 is a 12 bolt

8.795?????

here's a good ID chart for gaskets
http://www.kennysrodshop.com/fab/how2/differential.html

Big James XXXXL your correct about the 8.875, my bad.

Thanks for the chart. I'll get to the bottom of this, and I have a suspicion Advance had thier gaskets tagged wrong. Maybe pep-boys will have it...

p.s. how was power tour?

Now I'm 90% sure that my axle came from an Oldsmobile. It is a different 12 bolt pattern, no dimple on the cover, and would just be too easy for it to be a real 12 bolt. I plan on keeping it untill I can break it, and then I would like to get a 9 inch for the added strength, and I think I can do it for cheaper then a 12 bolt. maybe somebody knows if going with currie or moser will make a difference, or has one lying around...