1957 Rear Axles
All '57 Corvette rear axles are stamped with an alpha-numeric code, which identifies the build source, axle ratio, and date of manufacture.
The axle code is located on the front right or passenger side of the differential carrier at the same height as the axle tube. The axle code will read from left to right or bottom to top. The prefix or two-letter code designates the gear ratio and any other specific information about that rear differential. This code also refers to the manufacturer or source which built the rearend.
The numbers following the letter prefix designate the calendar month and day that axle was produced. From the 1955 through 1962 model years, the calendar month was designated by a one-number code from January (1) through September (9). The October through December codes were designated as 10-12, respectively. Beginning with the '63 model year, all month designations begin with a "0" so the January date code would show "01" instead of "1" as in previous years.
These rear axles were part of number 684 option code released approximately 3/1/57, which included heavy duty brakes and suspensions.
From Corvette By The Numbers by Alan Colvin, used with permission of Robert Bentley Publishers.