Help with Rear End ID

[Mike B.]

Can someone provide info including gear ratio etc for the following rear end?

Casting #3725899 F57 GM 25

Thanks in advance.

[William C.]

Re: Help with Rear End ID

The gear ratio info is stamped into the bottom flange, it cannot be discerned from casting numbers. What are the stamped numbers?

[John H.]

Re: Help with Rear End ID

That's a '57 non-posi diff, cast on June 5, 1957. The assembly date and ratio code is stamped on the front face of the passenger side of the housing; hard to see - will probably take some cleaning/wire-brushing to bring it up.