1971 El Camino Rear Axle Identification
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: RUC06421 decodes to RU ~ 3.31, C ~ Buffalo, 064 ~ day of year starting with January 1 (the 64th day being March 5), 1 or 2 ~ shift (if present).
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 |
| GD | 2.73 ~ Positraction |
| GF | 3.08 ~ 10-bolt |
| CH | 2.73 ~ 12-bolt Positraction (L48/350-4)* |
| GA | 2.56 ~ 10-bolt (L65/350-2)* |
| GC | 2.73 |
| GG | 3.36 ~ 10-bolt (base L6)* |
| GB | 2.56 ~ Positraction |
| GI | 3.36 ~ Positraction |
| KD | 2.73 ~ 12-bolt (L48/350-4)* |
| CW | 3.31 ~ 12-bolt (L48/350-4)* |
| CF | 3.31 ~ 12-bolt Positraction |
| RU | 3.31 ~ 12-bolt (LS5/454)* |
| RV | 3.31 ~ 12-bolt Positraction (LS5/454)* |
| RW | 4.10 ~ 12-bolt Positraction(LS5/454)* |
| GH | 2.73 ~ 10-bolt (L14/307)* |
| GN | 3.08 ~ 10-bolt (L14/307)* |
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| Code | Assembly Plant |
| C | Buffalo, N.Y. |
| G | Detroit Gear & Axle |
| K | McKinnon Industries (GM of Canada) |
| W | Warren, MI. |
Assembly Day - Day of the year, 000...365
Shift - 1 or 2 (or Day / Night) if applicable
KD ~ 2.73, K ~ McKinnon Industries, January 11th (11th day of year)
GN ~ 3.08, K ~ McKinnon Industries, February 21st (53rd day of year)
CH ~ Positraction 2.73, Buffalo, March 5 (64th day of year), 2nd shift,
Eaton Positraction
* Engine RPO code and size following the rear axle ratio are taken from build sheets 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.
