1971 Chevelle Rear Axle Date & Ratio Codes

The rear axle identification code consists of at least a two letter prefix indicating the gear ratio, a letter for the manufacturer's identity, and three digits indicating the day of the year from January 1 and other codes as necessary. The identification code should be stamped on the bottom or font of right axle tube either adjacent to the carrier housing or about 8" - 10" inboard from the backing plates. The particular engine RPO code is listed in parentheses as found on build sheets.

Example: RUC064 (1 or 2) decodes to RU - 3.31:1, C - Buffalo, 064 - day of year starting with January 1 (the 64th day being March 5), 1 or 2 - shift (if present). See bottom of page for photo examples.

Casting Numbers:
12-Bolt Casting #3969278
10-Bolt Casting #3969277

Casting date decode here →

The casting numbers/letters on rear end housings may have either a prefix or suffix of "N" or "NF" and no reason has been found yet why they may have one or the other.

Gear Ratio - First & second characters.

Prefix	Axle Ratio
CF	3.31:1 - 12-bolt Positraction (L48/350-4 & LS3/402)*
CH	2.73:1 - 12-bolt Positraction (L48/350-4 & LS3/402)*
CW	3.31:1 - 12-bolt (L48/350-4 & LS3/402)*
GA	2.56:1 - 10-bolt (L65/350-2)*
GB	2.56:1 - Positraction
GD	2.73:1 - Positraction
GF	3.08:1 - 10-bolt
GG	3.36:1 - 10-bolt (base I6 & L65/350-2)*
GH	2.73:1 - 10-bolt (L14/307)*
GI	3.36:1 - Positraction
GN	3.08:1 - 10-bolt (L14/307)*
KD	2.73:1 - 12-bolt (L48/350-4 & LS3/402)*
RU	3.31:1 - 12-bolt (LS5/454)*
RV	3.31:1 - 12-bolt Positraction (LS5/454)*
RW	4.10:1 - 12-bolt Positraction **

* Engine RPO code and size following the rear axle ratio are taken from build sheets or warranty Protect-O-Plate cards and may not reflect the only engine the rear axle codes came with. Where there are no RPO/engine information following the rear axle code only means I do not have build sheets to verify them. ** To date, no build sheet or other documentation has shown up with a Positraction 4.10:1 rear axle ratio. GM documentation for 1971 only shows a 4.10:1 available with the LS6 which was never released in the Chevelle for public sale. Additionally the RPO option ZQ9 for a performance axle only shows 302 of these options sold. The Positraction 4.10:1 and the 3.08:1 axle ratio are shown as available under ZQ9. With such a low sales of ZQ9 in 1971, one can conclude the 302 sales must be for the 3.08:1 ratio available as an option with the base 307 V8 that came standard with a 2.73:1 axle ratio. Rear Axle Assembly Plant - Third character
Code	Assembly Plant
C	Buffalo, New York
G	Chevrolet Gear & Axle, Detroit, Michigan
K	McKinnon Industries (GM of Canada)
W	Warren, Michigan

Assembly Day - Day of the year, 000...365

Shift - 1 or 2 (or Day / Night) if applicable

Examples

© ChevelleWorld
CHC - Positraction 2.73:1, Buffalo, N.Y., March 5, 1971 (64th day of year), 2nd shift, Eaton Positraction.

© ChevelleWorld
CFC - Positraction 3.31:1, Buffalo, N.Y., March 10, 1971 (69th day of year), 2nd shift, Eaton Positraction.

Casting Number Examples

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