REAR AXLE IDENTIFICATION

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 front left or right axle tube either adjacent to the carrier housing or about 8" - 10" inboard from the backing plates.

CX = 3.07:1
1028 = October, 28
B = Buffalo, N.Y. manufacturing location

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
CG 3.36:1 ~ Positraction
CH 2.73:1 ~ Positraction
CI 3.73:1 ~ Positraction
CJ 2.56:1
CK 2.56:1 ~ Positraction
CL 2.56:1
CM 2.56:1 ~ Positraction
CN 2.56:1
CO 2.56:1 ~ Positraction
CP 2.73:1
CQ 2.56:1
CS 2.56:1 ~ Positraction
CT 2.73:1
CW 3.31:1
*CX *3.07:1
CY 3.07:1
CZ 2.73:1
KA 3.55:1 ~ small ring gear (Note 1)
KB 2.56:1 ~ 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) (Note 1)
KE 2.73:1 ~ Positraction, small ring gear (Note 1)
KF 3.55:1 ~ Positraction, large ring gear (Note 1)
KG 3.08:1 ~ small ring gear (Note 1)
KH 3.08:1 ~ Positraction, small ring gear (Note 1)
KI 3.36:1
KJ 3.55:1 ~ large ring gear (Note 1)
KK 4.10:1 ~ Positraction
KL 3.36:1 ~ Positraction, small ring gear (Note 1)
KM 4.56:1 ~ Positraction
KN 3.55:1 ~ small ring gear (Note 1)
KO 4.88:1 ~ Positraction
KP 3.55:1 ~ Positraction, small ring gear (Note 1)
KQ 4.10:1 ~ Positraction, heavy duty
KX 3.07:1 ~ Positraction
FH 2.73:1
FI 2.73:1 ~ Positraction
FJ 3.08:1
FK 3.08:1 ~ Positraction
FL 3.36:1
FM 3.36:1 ~ Positraction
FN 3.55:1
FO 3.55:1 ~ Positraction

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