1964 Chevelle
1965 Chevelle
1966 Chevelle
1967 Chevelle
1968 Chevelle
1969 Chevelle
1970 Chevelle
1971 Chevelle
1972 Chevelle1968 Chevelle Rear Axle Date & Ratio Codes
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The rear axle identification code consists of a two letter prefix indicating the gear ratio, four digits indicating the assembly date as month/day, and a single letter suffix indicating the manufacturing location. 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: CG1025B decodes to CG - 3.36:1 Positraction, 1025 - Month [Oct] and Day [25], B - Buffalo (G=Chevrolet Gear & Axle, W=Warren, K=McKinnon Industries).
Casting Numbers:
12-Bolt Casting #3917124
10-Bolt Casting #3917123
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.
| Prefix | Axle Ratio |
| CA | 3.08:1 |
| CB | 3.36:1 |
| CC | 3.73:1 |
| CD | 3.07:1 - Positraction |
| CE | 3.08:1 - Positraction |
| CF | 3.31:1 - Positraction (L35/396)* |
| CG | 3.36:1 - Positraction |
| CH | 2.73:1 - Positraction |
| CI | 3.73:1 - Positraction |
| CJ | 3.08:1 |
| CP | 2.73:1 |
| CR | 3.70:1 - Positraction |
| CU | 3.73:1 - Positraction w/Metallic Brakes |
| CV | 3.70:1 |
| CW | 3.31:1 |
| CX | 3.07:1 |
| CY | 3.07:1 (L35/396)* |
| CZ | 2.73:1 (L35/396)* |
| FH | 2.73:1 - small ring gear (Note 1) |
| FI | 2.73:1 - Positraction, small ring gear (Note 1) |
| FJ | 3.08:1 (Base 230/base 307)* |
| FK | 3.08:1 - Positraction (L22/250 & 307)* |
| FL | 3.36:1 (L73/327)* |
| FM | 3.36:1 - Positraction |
| FN | 3.55:1 - small ring gear (Note 1) |
| FO | 3.55:1 - Positraction, small ring gear (Note 1) |
| FP | 3.70:1 |
| K2 | 3.55:1 |
| K3 | 3.55:1 - Positraction |
| K4 | 3.73:1 |
| K5 | 3.73:1 - Positraction |
| K6 | 4.10:1 - Positraction |
| K7 | 4.56:1 - Positraction |
| K8 | 4.88:1 - Positraction |
| KA | 3.55:1 - small ring gear (Note 1) |
| KB | 3.55:1 - Positraction, small ring gear (Note 1) |
| KC | 2.73:1 - Positraction, small ring gear (Note 1) |
| KD | 2.73:1 - large ring gear (Note 1) |
| KF | 3.55:1 - Positraction, large ring gear (Note 1) |
| KJ | 3.55:1 - large ring gear (Note 1) |
| KK | 4.10:1 - Positraction |
| KM | 4.56:1 - Positraction |
| KO | 4.88:1 - Positraction |
| KW | 2.73:1 - w/Metallic Brakes |
| KX | 3.07:1 - Positraction |
| KY | 3.31:1 - Positraction |
| KZ | 3.31:1 |
Note 1:
Just what constitutes a 'small' ring gear or 'large' ring
gear is uncertain. My Chevrolet Parts and Accessories Catalog, circa 1972, only
shows the gear ratio service part numbers so it is quite possible one or the other
was discontinued in favor of a 'service' part. Anyone with knowledge of the differences,
please contact me so I can share the information with all.
| Assembly Month - 1st and 2nd numbers | |||
| Number | Month | Number | Month |
| 01 | January | 02 | February |
| 03 | March | 04 | April |
| 05 | May | 06 | June |
| 07 | July | 08 | August |
| 09 | September | 10 | October |
| 11 | November | 12 | December |
Assembly Day - 3rd and 4th numbers
01...31
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Rear Axle Assembly Plant - 5th letter |
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| Code | Assembly Plant |
| B | Buffalo, New York |
| G | Chevrolet Gear & Axle, Detroit, Michigan |
| K | McKinnon Industries (GM of Canada) |
| W | Warren, Michigan |
* Engine RPO code and size following the rear axle ratio are taken from build sheets or Protect-O-Plate warranty 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 documentation to verify them.
Axle Ratio Code Stamps
CY 0824B for 3.07:1 ratio, August 24, 1967, Buffalo plant.
CF 0825B for Positraction 3.31:1 ratio, August 25, 1967, Buffalo plant.
CW 0109B for 3.31:1 ratio, January 9, 1968, Buffalo plant.
KF 0417B for Positraction 3.55:1 ratio, April 17 1968, Buffalo plant.
CF 0522B for Positraction 3.31:1 ratio, May 22, 1968, Buffalo plant.
Casting Date Examples
Casting date example of F 21 7 for June 21, 1967.
Casting date example of B 18 8 for February 18, 1968.
Casting date example of D 19 8 for April 19, 1968.
Casting date example of E 8 8 for May 8, 1968.
Casting Number Examples
1967-1969 -
Variations of casting number 3917124
