Transmission Date Codes...

[69Z28-RS]

From the CRG data, the date coding for '67-69 Transmissions follows the below code...

y  = model year (not calendar year)
   m  = month
        Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
        --- --- --- --- --- --- --- --- --- --- --- ---
         A    B    C     D    E    H    K   M     P   R     S    T    

What I don't understand, and I can't recall if I've ever heard the reason for..  is WHY did they skip the F, and G, and then the J  in the month codes?  I do understand why they didn't use the I for a month due to it's similarity to a '1'.. but why not F, G, and J (and a few other letters later in the alphabet)??

[bcmiller]

Gary, I am not sure why some of the letters were skipped.  There must have been a reason, but in the big scheme of things, it doesn't really matter.  We do know what they DID use.

F was possibly skipped because it was too close to an E .  G may have looked to close to being a 6.  J, maybe too close to a 3.

[69Z28-RS]

Thanks Byron,

I suppose the question is really..  WHY do transmission date codes *differ* from all other components dating?  The same issues re 'similarity' to other characters exist whatever the part is....  It just doesn't make sense to me.. 
You said you 'know' what it is:  HOW is that date coding ascertained?  Does it come from GM documentation?

[bcmiller]

Let me see if I can find any documentation on it.  I will post it if I can find it.

[JohnZ]

Let me see if I can find any documentation on it.  I will post it if I can find it.

It's probably in an obscure old issue of Chevrolet Service News - that's where stuff like that was usually published.

[69Z28-RS]

Let me see if I can find any documentation on it.  I will post it if I can find it.

It's probably in an obscure old issue of Chevrolet Service News - that's where stuff like that was usually published.

John,
Since apparently the same date coding applies to transmissions produced by several different plants, the code requirement must have come from a higher level GM directive.  Do you have any idea why transmission date coding differs from the date coding used on most other parts, differing even from other major parts like engines and differentials??

[JohnZ]

Since apparently the same date coding applies to transmissions produced by several different plants, the code requirement must have come from a higher level GM directive.  Do you have any idea why transmission date coding differs from the date coding used on most other parts, differing even from other major parts like engines and differentials??

I have no idea - apparently someone at Muncie had a reason to code it that way, but we have zero records from Muncie.

[69Z28-RS]

Apparently (from the CRG info), ALL transmissions are date coded with the same code (except for the beginning letter which denotes the factory).. so this would imply the date logic comes from a higher GM source than only Muncie, or any other of those plants...

[ZLP955]

On a related point, it's worth noting that the convention is slightly different for stamped versus cast date codes (http://www.camaros.org/numbers.shtml#GM-InternalDateCodes), and if you really want a puzzle to think over, try and understand the 66-70 LOF glass date coding format (http://www.camaros.org/glass.shtml#LOF).