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1972 El Camino Rear Axle Identification

 

 

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: CHC0642E1 decodes to CH ~ 2.73 Positraction, C ~ Buffalo, 064 ~ day of year starting with January 1 (the 64th day being March 5), 1 or 2 ~ shift (if present), E ~ Eaton Positraction

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
GD 2.73 ~ 10-bolt Positraction
GF 3.08 ~ 10-bolt
CH 2.73 ~ 10-bolt Positraction (L48/350-4)*
GC 2.73 ~ 10-bolt (L65/350-2)*
GG 3.36 ~ 10-bolt (L65/350-2)*
GI 3.36 ~ 10-bolt Positraction
KD 2.73 ~ 12-bolt (L48/350-4)*
CW 3.31 ~ 12-bolt (LS3/402)*
CF 3.31 ~ 12-bolt Positraction
RU 3.31 ~ 12-bolt (LS5/454)*
RV 3.31 ~ 12-bolt Positraction (LS5/454)*
RW 4.10 ~ 12-bolt
GH 2.73 ~ 10-bolt (L14/307)*
GN 3.08 ~ 10-bolt (L14/307)*

Assembly Day - Day of the year, 000...365

Shift - 1 or 2 (or Day / Night)

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

File Photo - 07/20/2009
CH ~ Positraction 2.73, Buffalo, NY, November 27 (321st day of year), 2nd shift, Eaton Positraction

03/10/2010
RU ~ 3.31, Buffalo, NY, April 18 (109th day of year), 1st shift.

* 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.