Does any one here know what number for Eaton or any well known axel makers for a 12 bolt cover 31 spline 3.42 gear rear end? Car is a 1968 442 with m21 455 engine. It is the original 3.42 gear 12 bolt cover rear axel with 31 spline axel shafts. I see a lot but am getting confused as they say one thing but show a 10 bolt cover picture. Other just say BOP but don’t elaborate wether 10 bolt is the cover or ring gear. Thanks Matt

 

Your axle is a Type O, used only in 1966-1970 Cutlass models. Most of the mainstream differential suppliers do not support this axle. It has a twelve bolt cover but only a ten bolt, 8.5" ring gear, and no, it is not the same as the 8.5" Chevy ten bolt axle. Be sure any differential you get for this axle is for a Type O. If the vendor doesn't know what that is, move along. Some aftermarket suppliers actually modify the differential from a Ford 8.8 to fit the Type O.

 

Thanks I know about the Chevy ones not being the same. I see a lot of guys swap the whole axel to Chevy ones but would like to stay original. I guess my best bet is just callling some of these guys on the phone direct.

 

Here's one source.

Jim at JDRace is another. Contact monzaz on this site. Actually, I suspect Jim will jump in here when he stumbles over this thread.