I admit it. I’ve been a Corvette geek for longer than I care to admit. Well, I just bought my second Corvette, this time a 1997 Fairway Green/Light Gray C5, and I have questions. Naturally. The following info might be of help to you and your Corvette, so, get yourself a cup of hot java and bear with me.

I’m trying to figure out if my RPO M30 auto transmission has been replaced, or what. The trans identification number is right where it should be, but something seems wrong. Etched into the case, facing down:

7YDD015 _ _ 7087598

OK, some of you are already saying, that can’t be the number! The first position digit is the model year – 1997 – and that’s fine, but it doesn’t make sense that the fifth position (calendar year) is a 0! The fifth position should be a 6 or a 7, signifying a 1996 or 1997 build date! Shouldn’t it? Blasphemy!

Settle down. Refill your coffee cup.

There is not a space between the second D and the 0. And, you’re correct: surely, the calendar year for the build date of the trans can’t be a 0 for a 1997 C5. Additionally, the two blank spaces reveal only the top half of two numbers due to a notch in the aluminum case. They seem to be the number 1 followed by the number 6, but it is truly impossible to tell. What’s more, I have no idea what the “7087598” ending sequence signifies.

Understandably, some of you are loudly grumbling that this sequence does not exactly reflect information found on the internet, which states that the alpha-numeric sequence for 1997 model year Corvette auto trans should be “7YDD6 _ _ _ _” or “7YDD7 _ _ _ _” depending on the calendar year of build (1996 or 1997). The blank spaces are a four number sequence, of which the first three are the Julian date build code – 001 is January 1, 365 is December 31.

Here’s my take on this villainous skullduggery. I will surmise that the one-digit calendar year, the 6 or 7, was omitted.

More coffee.

Here’s why: let’s say the 0 was supposed to be a 6 or 7. The next three numbers should be the Julian date build code. However, a Julian build date beginning with 15x would place the build date at May 30 (150) through June 8 (159) of either 1996 or 1997, both dates being unreasonable for a car built in February of 1997, which mine was. Of course, it is possible that the bone-head doing the etching mistakenly etched a 0 instead of a 6 or 7. Possible, but not likely, because of the May-June ramifications.

Let us now skip over to the “7087598”. Perhaps this sequence begins the Calendar date and Julian date: 7 being the calendar date (good), and 087 being the Julian date, the 87th day of the year. That can’t be correct because that date would put the trans build date at March 28, 1997 – much too late for my February 1997 build of the car.

Finish that cold coffee – grab a beer.

To me, a Julian build date of 015 makes more sense. That would place the build date of the transmission at January 15, 1997, just prior to the February 1997 build date of the car. Keep in mind that this was a fairly early production car, VIN 1160. If the build date really is 015, then the one-digit calendar year was omitted in the etched sequence.

What do you think? Am I missing something? Was the one-digit calendar year in the trans number sequence omitted?

Ps: the engine build date was February 7, 1997: the 38th day of 1997: “97” with Julian date “038” = 10ZYD W970380080

pss: this is the C5 General forum - should this have been posted in the C5 Tech forum?

 

Very interesting and well written! You have talent there.

 

Thanks, o2bnkc!