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  1. #1
    Join Date
    Jan 2004
    Location
    East Tennessee
    Posts
    4,581

    Default W Olds rearend codes? W-27

    We have a 70 W-31 with a 12 bolt cast iron rearend with a code of TO stamped in the axel housing. I have read where that is correct for a 391 gear. But, I have learned I can't believe what I read. So, is it correct?

    Also, we bought a W27 rearend with SX on it. What's that stand for.

    One more. This other W27 rear from Wisconsin has what looks to be a SZ on it. The S looks pretty good, but the Z is very hard to read. What's it stand for?

    Thanks in advance.
    1971 GS455
    1971 Riviera GS
    John Ayers

  2. #2
    Join Date
    Aug 2006
    Location
    Medford Oregon
    Posts
    73

    Default Re: W Olds rearend codes? W-27

    Wow, you are one lucky guy to have those parts! According to my "By the Numbers" book from supercarsunlimited the codes are as follows:

    TO 1967-70 3.91 Posi, 1971-72 3.73 posi

    W27 rears
    SV 3.23 Posi
    SX 3.42 Posi
    SZ 3.91 Posi

    If you decide to clean house and throw one of these out throw it my way!!!
    John

  3. #3
    Join Date
    Jan 2004
    Location
    East Tennessee
    Posts
    4,581

    Default Re: W Olds rearend codes? W-27

    Thanks John. Glad you showed me the difference in the TO code. I wondered if it changed ratios in 1971. Also, glad to see a SZ on the other. I was having a hard time reading the Z. They had a horrible stamp when they punched it years back. I hope we don't get in the situation where we don't have to clean house. It took too long to find these.
    1971 GS455
    1971 Riviera GS
    John Ayers

  4. #4
    Join Date
    Feb 2002
    Posts
    3,966

    Default Re: W Olds rearend codes? W-27

    2 letter codes are reused in different years and meant different things. In 1971, Olds stopped using their own design 12 bolt rear end and began manufacturing and using the corporate 10.5 design.

    The two letter codes were used to build the cars originally, not identify them later. Actual part number stamps are about the only positive id even though we didn't use them in the assembly plant. The broadcast "build sheets" referred to these codes in the mfg. process.

    The assembly lines were stripped of non carryover parts as the last car went down the line for the model year. Carryover parts were moved to the new point of use location (if relocated due to a process or line layout change.) As long asa the old parts wer removed from the plant, the same 2 letter code was reused on new year parts.
    Aspire to inspire, before you expire.

 

 

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