1968 Rear Axle

Rear Axle Ratios - 1968

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

Rear Axle Assembly Plant - 5th letter
Code	Assembly Plant
B	Buffalo, NY
G	Chevrolet Gear & Axle
W	Warren, MI
K	McKinnon Industries

* 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