1972 Chevelle Rear Axle Identification

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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 GM Division, and three digits indicating the day of the year from January 1. 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: CHC064 decodes to CH ~ 2.73:1 Positraction, Chevrolet ~ Buffalo, 064 ~ day of year starting with January 1 (the 64th day being March 5, 1972), 1 or 2 ~ shift (if present), E ~ Eaton Positraction. 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 (LS3/402)*
CH 2.73:1 ~ 12-bolt Positraction (L48/350-4 & LS3/402)*
CW 3.31:1 ~ 12-bolt (LS3/402 & L48/350-4)*
GA 2.56:1 ~ 10-bolt
GC 2.73:1 ~ 10-bolt (L65/350-2)*
GD 2.73:1 ~ 10-bolt Positraction (L65/350-2)*
GF 3.08:1 ~ 10-bolt
GG 3.36:1 ~ 10-bolt (L65/350-2)*
GH 2.73:1 ~ 10-bolt (L14/307)*
GI 3.36:1 ~ 10-bolt 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 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 1972 does not show a 4.10:1 available as a performance ratio for any engine. Additionally the RPO option ZQ9 for a performance axle only shows 296 of these options sold. The 3.08:1 axle ratio is shown as available under ZQ9. With such a low sales of ZQ9 in 1972, one can conclude the 296 sales must be for the 3.08:1 ratio available as an option with the base 307 V8 in a sport coupe or convertible that came standard with a 2.73:1 axle ratio.

Assembly Day - Day of the year, 001...365 for 1971 and 001 through approximately 244 for 1972.

Shift - 1 or 2 (or Day / Night)

Rear Axle Assembly Plant - last character
Code Assembly Plant
C Buffalo, NY
G Detroit Gear & Axle
K McKinnon Industries (GM of Canada)
W Warren, MI


GC ~ 2.73:1, C ~ Buffalo, NY, August 3 (215nd day of 1971), 2nd shift


GC ~ 2.73:1, C ~ Buffalo, NY, August 20 (232nd day of 1971), 2nd shift


GH ~ 2.73:1, C ~ Buffalo, NY, September 16 (259th day of 1971), 2nd shift


CF ~ Positraction 3.31:1, C ~ Buffalo, NY, October 5 (278th day of 1971), 2nd shift, Eaton Positraction


RV ~ Positraction 3.31:1, C ~ Buffalo, NY, November 26 (320th day of 1971), 2nd shift, Eaton Positraction


CH ~ Positraction 2.73:1, C ~ Buffalo, NY, November 27 (321st day of 1971), 2nd shift, Eaton Positraction


KD ~ 2.73:1 ~ C ~ Buffalo, NY, November 23 (327th day of 1971), 1st shift


RU ~ 3.31:1, C ~ Buffalo, NY, April 18 (109th day of 1972), 1st shift

Casting Date Examples

Examples welcomed...

Casting Number Examples




1970-1972 ~ Variations of casting number 3969278