C1 rear end

[dale edlund]

Recently purchased a 1960 Corvette. The rear end has a casting #3707306 on front drivers side. It also has a stamped #BB331 or BP331 (I think) on front passenger side. Can anyone tell me where this rear end came from? Also do any of these numbers tell the ratio? Did the wheel spin thing and it came out as 3:70 ratio, it is not positraction. Thank you

[James F.]

Re: C1 rear end

Dale,
The 306 is a '55-'56 Corvette & passenger rear end (this info from a '56 parts book). The date code on mine is cast on a line right below the cast 3707306. BB or BP is probaably a sedan ratio code. I don't have this information. Regards.

[Terry D.]

Re: C1 rear end

The "BB" code is for a 56-58 passenger with automatic transmission. In 57 and 58 it was a 3:36 and in 56 it was a it was a 3:55 ratio. Hope this helps. By the way if you keep this rear end and go to replace axle bearings, they are specific to 56-57, as they are smaller than the 58-62 bearings. Good source is Case's Chevy parts, reasonable prices and friendly knowledgable people.
Terry

[Tom P.]

Re: C1 rear end

The 55-6 Pass car and 56 Vette axle bearings are the same (bearing OD is 2.8346, ID is 1.3780, width is 1.3130).
The 57 Pass car and Vette axle bearings are the same (bearing OD is 3.000, ID is 1.3780, width is 1.2930.
The 58-64 Pass car and 58-62 Vette axle bearings are the same (bearing OD is 3.000, ID is 1.3780, width is 1.4200).
As you can see, all the axle bearings have the same ID (and use the same lock ring). BUT, the OD is different for 56 and 57-64, thus, a 56 HOUSING has a different size opening on each end from the 57-64 housings. The only difference between a 57 and a 58-64 bearing is the thickness. The axle bearings for posi rearends were roller, rather than ball. But they are no longer available.
Axle bearings have NOTHING WHATSOEVER to do with the center section, pumpkin, differential, whatever you wish to call it. The axle bearings are only specific to the ends of the housing and the axles themselves.
The 55-64 pinion and side carrier bearings are the same (even though the parts books don't show the side carrier bearings are the same for 55-6).