1971 SS-Optioned Chevelle

1971 SS-Optioned Malibu

Rear End Gear Ratio/Codes

Depending on the engine, the rear end could be a 10-bolt or 12-bolt. Casting number for the 10-bolt is #3969277 and the 12-bolt is #3969278.

The rear axle identification code consists of at least a two letter prefix indicating the gear ratio, a letter for the manufacturer's identity, and three digits indicating the day of the year from January 1 and other codes as necessary. 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: RUC064 (1 or 2) decodes to RU ~ 3.31:1, C ~ Buffalo, 064 ~ day of year starting with January 1 (the 64th day being March 5), 1 or 2 ~ shift (if present). See bottom of page for photo examples.

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.

Prefix	Axle Ratio
CCF	3.31:1 ~ 12-bolt Positraction (L48/350-4 & LS3/402)*
CCH	2.73:1 ~ 12-bolt Positraction (L48/350-4 & LS3/402)*
CCW	3.31:1 ~ 12-bolt (L48/350-4 & LS3/402)*
CGA	2.56:1 ~ 10-bolt (L65/350-2)*
CGB	2.56:1 ~ Positraction
CGD	2.73:1 ~ Positraction
CGF	3.08:1 ~ 10-bolt
CGG	3.36:1 ~ 10-bolt (base L6 & L65/350-2)*
CGH	2.73:1 ~ 10-bolt (L14/307)*
CGI	3.36:1 ~ Positraction
CGN	3.08:1 ~ 10-bolt (L14/307)*
CKD	2.73:1 ~ 12-bolt (L48/350-4 & LS3/402)*
CRU	3.31:1 ~ 12-bolt (LS5/454)*
CRV	3.31:1 ~ 12-bolt Positraction (LS5/454)*
CRW	4.10:1 ~ 12-bolt Positraction **

* Engine RPO code and size following the rear axle ratio are taken from build sheets or warranty Protect-O-Plate 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 build sheets to verify them. ** To date, no build sheet or other documentation has shown up with a Positraction 4.10:1 rear axle ratio. GM documentation for 1971 only shows a 4.10:1 available with the LS6 which was never released in the Chevelle for public sale. Additionally the RPO option ZQ9 for a performance axle only shows 302 of these options sold. The Positraction 4.10:1 and the 3.08:1 axle ratio are shown as available under ZQ9. With such a low sales of ZQ9 in 1971, one can conclude the 302 sales must be for the 3.08:1 ratio available as an option with the base 307 V8 that came standard with a 2.73:1 axle ratio. Rear Axle Assembly Plant - Third character
Code	Assembly Plant
C	Buffalo, N.Y.
G	Detroit Gear & Axle
K	McKinnon Industries (GM of Canada)
W	Warren, MI.

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

Shift - 1 or 2 (or Day / Night) if applicable

See the engines page for engine/transmission breakdown.

Transmission

The 1971 SS Chevelles required any optional transmission, leaving out any engine with the 2-speed Powerglide transmission.

Power Teams - Sport Coupe/Convertible

El Camino

Monte Carlo

Manual Transmission

Several 3- and 4-speed transmissions were used. Of the two different 3-speed manual transmissions the 270hp L48 has a low gear of 2.54:1 and the 360-hp LS3 has a low gear of 2.42:1. Three different 4-speed manual transmission were used. The two 350 cid engines and the 402 cid engine could opt for the wide ratio RPO M20 transmission while the 365hp 454 cid engine mandated the close ratio heavy duty M22 when a 4-speed was chosen by the customer.

TH350 Turbo-Hydramatic

For the first time, the TH350 3-speed automatic transmission can be found in an SS-optioned Chevelle and was used behind both 350 cid engines.

TH400 Turbo-Hydramatic

Several TH400 automatic transmissions were used with both the 402 cid 330hp LS3 and the 454 cid 365hp LS5.These can be identified by (1) their color and (2) their code. This tag is riveted to the passenger side of the transmission and contains valuable data if you're concerned with originality. The number stamped in the middle (such as the 218 on the first example) is the Julian date starting on January 1, 1970. So a Julian date of 218 is the 218th day counting from January 1, 1970 or August 6, 1970

If the Julian date is 365 or greater then the transmission was built in 1971 like the last example with a Julian date of 463. Subtract 365 from 463 and you get 98, or April 8, 1971.

The 4- or 5-digit number on the bottom right of the tag is simply the transmission's serial number and of no consequence as far as dating it goes.