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I thought I would share some info with you guys since I'm going through it right now. Differential identification always seems to be a difficult one. For starters, the location of the ident. numbers are on the bottom of the diff on the flat spot between where the spring bolts to and the rear diff cover. Sorry about the condition of the arrow.
Ok, here's and example of how to read the numbers.Lets say the stamp reads OH C2181 . OH is the axle code or prefix, the C is the assembly plant, the 218 is the day of the year and the 1 is the shift. The OH represents a 78-79 3:55 ratio diff.
Other axle prefixes or codes are as follows, I'm sure this site will cover most. It's very informative.It takes any mystery out of decoding.
AW is 3.08 in all the years that code was used (68 through 75, including 73). All C3 diffs were posi from 71-82, but it was possible to have an open diff before that. I don't know how to decode your diff's birthday, though.
Last edited by Bikespace; Sep 11, 2021 at 03:16 AM.
W341 indicates built at the Warren (MI) plant on the 341st day of (presumably) 1972 which would be Wednesday, December 6. I say presumably because I don’t know if the differential is original to your car. Look on the left side of the casting for a raised date code like in the example below. What’s the last 5 of your VIN?
The E indicates an Eaton posi unit was installed and the 1 indicates the differential was built on the 1st shift.
AW was a 308 gear. W warren, 2nd shift I believe, 291 the day of the year. Look at the lower left side for the casting date, will be a letter and 2-3 numbers. So say B12 8= Feb 12 1968 or 1978. I think 1971 started with the Julian dating, prior had the actual date stamped in, ie: Oct12 69.
Differential Identification
