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Thread: 1991 gear ratio

  1. #1
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    1991 gear ratio

    I have a 4x4 blazer with a 4.3 and a 700r4.
    I blew the 8.5 rearend to little pices doing a standstill.
    My problem is i cant find any of the codes in the glove box. I cant even find anything on the rear axle.
    So i pulled the diff cover and i noticed i had a lsd or whatever.
    What i need to know is how many different gear ratios did they run with the options my truck has?

    Thanks,
    Jordon

  2. #2
    Registered User atomsmasher's Avatar
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    You might call the local salvage yard that has a Hollander interchange. They can give you the list of what came with the truck. That should at least head you in the correct direction until you get a count on the gear ratio.
    Those who dream by day are cognizant of many things which escape those who dream only by night.

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  3. #3
    Registered User L98Jimmy's Avatar
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    You should be able to go to any gm dealer parts department and have them decode the vin for you. That will at least tell you what the truck came with from the factory.
    Women come and go but you can rely on a truck.

  4. #4
    Administrator Blazin Low's Avatar
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    For one, no 1991 Blazer came with a 8.5" rear

    if its stock, its either a 7.5" or 7.625"

    Common gear ratios were 3.42 or 3.73, and possibly 4.11.

    Cant you just count the number of teeth on the ring and pinion and do some math? Im pretty sure you can calculate it like that.
    this is a test of the sig

  5. #5
    Registered User Myself's Avatar
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    Yes, or even read the numbers off the ring gear as it should be matched and show the tooth count.

  6. #6
    5.7L VORTEC 350 blazin4low's Avatar
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    there should be numbers stamped on the face of the pinon gear and numbers stamped on the ring gear. take the two numbers on one of the gears and divide the big number by the small number and get your ratio......example 13-40 is stamped on the gear 40/13=3.0769 which would be a 3.08 gear. you can also use this if your math is bad http://www.csgnetwork.com/rnggrpinioncalc.html

    numbers on ring gear


    numbers on pinion
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