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  1. #1
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    Default Differential Casting Numbers

    Can anyone help me decode the casting numbers on my 68 Coupe differential? The numbers cast on it are as follows: 2 AT 71 W. Thanks for any help.

  2. #2
    Member 6880 Mike's Avatar
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    AT is the code for 3.08:1 posi for big blocks; W indicates the Warren, Michigan plant. I believe the 2 is for the second shift and 71 is the year.


  3. #3
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    Quote Originally Posted by 6880 Mike View Post
    AT is the code for 3.08:1 posi for big blocks; W indicates the Warren, Michigan plant. I believe the 2 is for the second shift and 71 is the year.

    That is what I was thinking Mike, but I did not see the AT as an option code in 1971. I know it now has 3.70 gears but was just curious as to what it may have had in it at birth. Thanks for the information.

  4. #4
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    Member Vettehead Mikey's Avatar
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    I believe the '71' would be the 71st day of the year the diff was assembled. What's the casting date of the case itself?

  5. #5
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    Quote Originally Posted by Vettehead Mikey View Post
    I believe the '71' would be the 71st day of the year the diff was assembled. What's the casting date of the case itself?

    I do not have that number. Can it be viewed from under the car or does the differential have to be out? Thanks.

  6. #6
    Member GTR1999's Avatar
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    The casting # is on the lower LH side of the diff. A letter and 2-3 numbers- A 238 = Jan 23 1968 or 1978.

    If you have a 71 chances are someone blew up the original 68 posi case. The 63-64 & 65-69 cases were not the best. The 3's 4's were junk, the 5-9" not much better. The '71-9 cases were better, had better spiders, but lousy clutches. Sounds like someone was in there, just hope they built it correctly and addressed the weak areas in there.
    Gary
    GTR1999

  7. #7
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    Quote Originally Posted by GTR1999 View Post
    The casting # is on the lower LH side of the diff. A letter and 2-3 numbers- A 238 = Jan 23 1968 or 1978.

    If you have a 71 chances are someone blew up the original 68 posi case. The 63-64 & 65-69 cases were not the best. The 3's 4's were junk, the 5-9" not much better. The '71-9 cases were better, had better spiders, but lousy clutches. Sounds like someone was in there, just hope they built it correctly and addressed the weak areas in there.

    Thanks to everyone for the good information. I'm going to crawl under this weekend and check out the other numbers. I guess it really doesn't matter one way or the other, but I am always interested in finding out a bit more history on my car. Thanks again.

  8. #8
    Member GTR1999's Avatar
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    Quote Originally Posted by lhdg865 View Post
    Thanks to everyone for the good information. I'm going to crawl under this weekend and check out the other numbers. I guess it really doesn't matter one way or the other, but I am always interested in finding out a bit more history on my car. Thanks again.

    Here it is, this is a cleaned up diff I built for a guy- Now for you sharpies out there what year is this for?

    Gary
    GTR1999

  9. #9
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    Quote Originally Posted by GTR1999 View Post
    Here it is, this is a cleaned up diff I built for a guy- Now for you sharpies out there what year is this for?


    Let me see if I have learned anything...How bout October 18th 1963 or 1973???

  10. #10
    Member GTR1999's Avatar
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    Quote Originally Posted by lhdg865 View Post
    Let me see if I have learned anything...How bout October 18th 1963 or 1973???
    That is correct it is a 10/18/63 casting used in a 1964 corvette. The thing that really confirms it as a 63 housing, by just that picture, is the front bracket hole is tapped 7/16-14 where as 65-79 housings had thru holes for both bolts.

    Good job
    Gary
    GTR1999

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