1964 Chevelle
1965 Chevelle
1966 Chevelle
1967 Chevelle
1968 Chevelle
1969 Chevelle
1970 Chevelle
1971 Chevelle
1972 Chevelle1971 Chevelle Rear Axle Date & Ratio Codes
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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
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 ** |
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* 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 |
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| 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
RUC - 3.31:1, Buffalo, N.Y, January 9th (9th day of year), 2nd shift.
KD - 2.73:1, K - McKinnon Industries, January 11th (11th day of year)
GN - 3.08:1, K - McKinnon Industries, February 21, 1971 (53rd day of
year)
CHC - Positraction 2.73:1, Buffalo, N.Y., March 5, 1971 (64th day of
year), 2nd shift, Eaton Positraction.
CFC - Positraction 3.31:1, Buffalo, N.Y., March 10, 1971 (69th day of
year), 2nd shift, Eaton Positraction.
RVC - Positraction 3.31:1, Buffalo, N.Y., August 3, 1970 (215th day
of year), "B" is unknown.
KDC - 2.73:1, Buffalo, N.Y., August 17, 1970 (229th day of year), "A"
is unknown
Casting Number Examples
1970-1972 - Variations of casting number 3969278.
