1964 Chevelle Rear Axle Identification

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

Example: YB 1025 decodes to YB ~ 3.36:1, 1025 ~ Month [Oct] and Day [25]

Casting Numbers:
10-Bolt Casting #3839390N

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
LA 3.08:1 ~  3 or 4-speed
LB 3.36:1 ~  3 or 4-speed
LG 3.08:1 ~  Positraction
LH 3.36:1 ~  Positraction
YA 3.08:1 ~  3 or 4-speed
YB 3.36:1 ~  3 or 4-speed
YG 3.08:1 ~  Positraction
YH 3.36:1 ~  Positraction
ZA 3.08:1 ~  found with Powerglide transmission
ZB 3.36:1 ~ 
ZC 3.08:1 ~  w/Metallic Brakes
ZD 3.36:1 ~  w/Metallic Brakes
ZE 3.08:1 ~  Positraction w/Metallic Brakes
ZF 3.36:1 ~  Positraction w/Metallic Brakes
ZG 3.08:1 ~  Positraction
ZH 3.36:1 ~  Positraction
ZJ 3.70:1 ~  w/Overdrive
ZK 3.70:1 ~  Positraction
ZL 3.70:1 ~  w/Metallic Brakes
ZM 3.70:1 ~  Positraction w/Metallic Brakes
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
* It's not unusual for the month to be a single digit number

Assembly Day - 3rd and 4th numbers
01...31

Rear Axle Assembly Plant - 5th letter

Code Assembly Plant
B Buffalo ~  New York
G Chevrolet Gear & Axle
W Warren ~  Michigan
K McKinnon Industries

09/06/2011
ZA ~ 3.08:1 ~ 3 or 4-speed - June 23

Casting Date Examples

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Casting date example of H 20 4 for August 20, 1964