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finding gear ratios.....

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by big_truxx, Oct 27, 2004.

  1. big_truxx

    big_truxx 1/2 ton status

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    /forums/images/graemlins/1zhelp.gif i was trying to figure out some diff's ratios today but as ive never done it before think i did it wrong. i thought you jacked a wheel up till it will spin and rotate the driveshaft till the tire rotated one full time and that was yer ratio. but both my dana 70 and 14 bolt were both about 2:1 lol i dont think thats whats in there. did i do this wrong? /forums/images/graemlins/dunno.gif
     
  2. Rolled

    Rolled 1/2 ton status

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    On the ring gear, there will be some numbers stamped. They are the number of teeth on the ring and pinion. Divide them to get the ratio.

    Example of a 3.73 setup:

    41 11 will be stamped on the ring.

    41 = ring teeth
    11 = pinion teeth

    41/11 = 3.7272727272727
     
  3. big_truxx

    big_truxx 1/2 ton status

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    /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif /forums/images/graemlins/peace.gif thanks u rock!! i knew there was a reason those #'s were there just not knowing what they meant. and knew how to divide the #'s but couldnt count the pinion. now im straight. thanks.
     
  4. spearchucker

    spearchucker 1/2 ton status

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    Or if you don't want to remove the diff cover, make a mark on the driveshaft and have someone slowly drive forward until the tires make one revolution. The number of times the driveshaft rotates would be your ratio.
     
  5. mofugly13

    mofugly13 1 ton bucket of rust Premium Member

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    If you only jack up only one side and count the driveshaft rotations, you will need to multiply your count by two. Sounds like you've got 4.11's in there.
     
  6. big_truxx

    big_truxx 1/2 ton status

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    when i looked at my 3/4 ff rear, the #'s at the end of everything were; 41 7 75 now does that mean that the ratio is really 5.86???
     
  7. dave_90_blazer

    dave_90_blazer 1/2 ton status

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    [ QUOTE ]
    when i looked at my 3/4 ff rear, the #'s at the end of everything were; 41 7 75 now does that mean that the ratio is really 5.86???

    [/ QUOTE ]

    thats what it comes to, to be sure, pull the cover and count teeth, 41 on the ring and 7 on the pinion
     
  8. big_truxx

    big_truxx 1/2 ton status

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    hmmm i counted 41 on ring but the pinion seemed hard to count if it was possible at all. 5.86 is a fairly low gear /forums/images/graemlins/peace.gif
     
  9. spearchucker

    spearchucker 1/2 ton status

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    I think there was a post about this a few weeks ago. If I recall correctly the gears were made in July '77 (7 75) and the ring gear has 41 teeth. The pinion count would be the number just before the 41. When you get that just divide 41 by that number and there's your ratio. /forums/images/graemlins/thumb.gif
     
  10. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    I think there was a post about this a few weeks ago. If I recall correctly the gears were made in July '77 (7 75) and the ring gear has 41 teeth. The pinion count would be the number just before the 41. When you get that just divide 41 by that number and there's your ratio. /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    That is correct. /forums/images/graemlins/thumb.gif
     
  11. big_truxx

    big_truxx 1/2 ton status

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    the # before the 41 was a 1 /forums/images/graemlins/dunno.gif
     
  12. walla2k5

    walla2k5 1/2 ton status

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    How to I.D. your gear ratio: Count the number of teeth on your ring gear and divide by the numer of teeth on your pinion gear. The result is your gear ratio

    Ring gear: 43 teeth.....Pinion 14 teeth....

    43 divided by 14 equals 3.07 /forums/images/graemlins/usaflag.gif
     
  13. Emmettology 101

    Emmettology 101 3/4 ton status

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    What is the complete string of numbers on your ring gear?
     
  14. 87BrnRsd

    87BrnRsd 1/2 ton status

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    [ QUOTE ]
    hmmm i counted 41 on ring but the pinion seemed hard to count if it was possible at all. 5.86 is a fairly low gear /forums/images/graemlins/peace.gif

    [/ QUOTE ]
    5.86 is not a fairly low gear. Its a REALLY low gear. GM did not put this ratio in any of their axles (except maybe military or extremely heavy duty applications /forums/images/graemlins/dunno.gif) I believe the lowest factory GM ratio is 4.56 and was found in 1 ton military 14 bolts that came from the factory with a detroit locker. I know this because I happen to have one sitting under my K5. Give us the complete line of numbers stamped on your ring gear, and we can figure out your ratio.
    -Harrison
     
  15. big_truxx

    big_truxx 1/2 ton status

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    these are the #'s on the ring;

    GM 3992484 1' 41 7 75

    i also counted 41 teeth on the ring. but was unable to count the pinion teeth.
     
  16. JeremyK5

    JeremyK5 1/2 ton status Premium Member

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    There shouldn't be an apostrophe in that string of numbers, so it is most likely a 1, and not an apostrophe. So you have 3.73 gears.
     
  17. big_truxx

    big_truxx 1/2 ton status

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    thats what i was kinda thinkin. the 2nd 1 didnt stamp correctly. i also saw on the pinion a 41 and an 11 this morning when i went to look at the ' again. thanks all for your help educating me on gear ratios!!!! /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif
     
  18. 87BrnRsd

    87BrnRsd 1/2 ton status

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    Yep, 3.73's. Now that you know what the ratio is, time to get LOWER gears. /forums/images/graemlins/thumb.gif
    -Harrison
     
  19. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    Yep, 3.73's. Now that you know what the ratio is, time to get LOWER gears. /forums/images/graemlins/thumb.gif
    -Harrison

    [/ QUOTE ]

    5.13s /forums/images/graemlins/deal.gif
     
  20. 87BrnRsd

    87BrnRsd 1/2 ton status

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    /forums/images/graemlins/peace.gif
    -Harrison
     

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