What is my ratio?

Discussion in 'Differential & Driveline' started by Iowan, Sep 13, 2017.

  1. Iowan

    Iowan Full Access Member

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    I crawled all over the axle and have no idea what I found

    IMG_2556.JPG
     
  2. Iowan

    Iowan Full Access Member

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    Can this be upside down? I found the GM21 too which I've never heard of. Thanks guys!
     
  3. spanky55amg

    spanky55amg Full Access Member

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    That looks like a casting number for the rear end itself. Now Im not a rear guru, but, the rear ends used to be tagged on one of the cover bolts, but it being 37 years old, thats not there. I think the only way you will be able to know is to count the ring and pinion gear teeth.
     
  4. CSFJ

    CSFJ Supporting Member Supporting Member

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    The ratio should be stamped on the edge of the ring gear. If you're going to open it to count teeth, I'd look for that instead.
     
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  5. spanky55amg

    spanky55amg Full Access Member

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    see.... I knew someone would know more than I do.
     
  6. Jerry phillion

    Jerry phillion Junior Member

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    Calvin, is it a posi rear end or an open rear end? If posi, put truck
    In neutral gear, block front wheels. Then jack up truck so both back wheels are off ground. Now make chalk mark on either tire
    Facing ground. Also make mark on driveshaft facing ground.
    Rotate back wheel one complete revolution while counting
    Driveshaft revs. Example: if it's a little over 3 revs it's a 3:08 .
    If it's less maybe a 2:73 etc. if open rear end drop Opposite wheel to ground , then do same wheel/driveshaft procedure. Done.
    Jerry
     
  7. Iowan

    Iowan Full Access Member

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    Thanks and I have one more picture too

    IMG_2766.JPG
     
  8. Iowan

    Iowan Full Access Member

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    G239
     
  9. Iowan

    Iowan Full Access Member

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    It took 1 and then some
     
  10. Iowan

    Iowan Full Access Member

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    Not much just about maybe an 3/8 more of a turn
     
  11. Jerry phillion

    Jerry phillion Junior Member

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    You have to double the amt of turns. I may have forgotten
    Yo mention that. It looks like a 2:73 gear.
     
  12. Iowan

    Iowan Full Access Member

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  13. spanky55amg

    spanky55amg Full Access Member

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    Haha, Im glad this got solved b/c Im about to count mine. I was wondering if Iowan had counted correctly. Hahaha.
     
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  14. Iowan

    Iowan Full Access Member

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    I wondered too, I even did both sides but that's also how you find out if you have a posi, I do not.
     

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