Results 1 to 6 of 6

Thread: 1991 gear ratio

  1. #1
    Registered User
    Join Date
    Jan 2013
    Homer, Alaska

    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?


  2. #2
    Registered User atomsmasher's Avatar
    Join Date
    Mar 2007
    Northwest Louisiana
    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.

    Edgar Allan Poe

  3. #3
    Registered User L98Jimmy's Avatar
    Join Date
    Sep 2005
    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
    Join Date
    Oct 2001
    In Front of You
    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
    Join Date
    Aug 2003
    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
    Join Date
    Aug 2002
    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

    numbers on ring gear

    numbers on pinion
    Tuned by Bland Tuning
    Transmission built by Transbuilderguy on FSC!
    Marine Intake swap by me

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts