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HELP < need list of GM R&P ratios

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by K10ANDYKHAMNIC, Apr 4, 2003.

  1. K10ANDYKHAMNIC

    K10ANDYKHAMNIC 1/2 ton status

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    yes i searched . i opened my 10 bolt front the other day and read the numbers on the ring gear and it appears to have 2.56 gears ! no wonder my truck was gutless but had top end out the wazoo....i thought it was just the 305 but no . thanks -Andy
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Thought the only K5 available ratios were 2.73, 3.08, 3.42, and 3.73 since about the day of their inception.

    I'd be real surprised if 2.56's made it into any 73-87 truck, and even more surprised if they were put in 4wd's of that vintage.

    2.56's were fairly popular in cars of the 80's, but 2.73's are even fairly uncommon in trucks compared to the 3.08's. Of course someone could have swapped them in, but, why? That would just be scary!

    You sure you didn't figure part of the date code for the ring/pinion count? No offense, but it's happened before, the numbers made sense, and came out to a possible combo. /forums/images/graemlins/smile.gif
     
  3. wrathORC

    wrathORC 1/2 ton status

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    Gear Ratios:
    Code Ratio
    GU2 2.73
    GU4 3.08
    GU5 3.23
    GU6 3.42
    GT4 3.73
    GT5/GT8 4.10


    FOR TEN BOLT ONLY (I don't know if it works for Dana 44s):
    Ratio Ring Pinion
    2.73 41 15
    3.08 40 13
    3.23 42 13
    3.42 41 12
    3.73 41 11
    4.10 41 10
    4.56 41 9
    4.88 39 8
    5.13 41 8


    As you can see, with any axle ever put in a pickup by GM you can get the ratio off the pinion gear alone for a ten bolt. GM never put 3.23 gears in a pickup. They used 2.73s, 3.08s, 3.42s, 3.73s, and 4.10s.
     
  4. K10ANDYKHAMNIC

    K10ANDYKHAMNIC 1/2 ton status

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    ill take a pic of it just to make sure , did they make 2.56 s for the 12 bolt also ? as for my any error on my part i had Arq there and we tried using different numbers but they would have been lower and i know that my truck wouldnt have been so gutless . is thera any way to tell if they are original ? it wouldnt be on the glove box sticker ? thanks -Andy
     
  5. Hossbaby50

    Hossbaby50 3/4 ton status

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    My gear ratio was on the glovebox sticker. It was the optional 3.73 gearset, so it was on the options list on the glovebox sticker. If yours is that low it probably won't be though. Might have the options code though.
     
  6. R72K5

    R72K5 Banned

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    2.76 12 bolt
    2.73 10 bolt
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Dunno. Thought car and truck 12 bolts were different, and if so, I can't see 2.56 being available for the trucks.
     
  8. 84_Chevy_K10

    84_Chevy_K10 Banned

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    2.73s were very common in the '80s. My '84 came with them. It was the, "Standard" ratio.
     

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