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1980 K10 4x4 with 350 Rear End Need Gear ratio

Discussion in 'Differential & Driveline' started by mejiar1969, Apr 21, 2019.

  1. mejiar1969

    mejiar1969 Junior Member

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    Location:
    Adkins tx
    First Name:
    Rick
    Truck Year:
    1980
    Truck Model:
    Chevrolet
    Engine Size:
    350
    I’m fixing up a a this truck. The rear end needs to be replaced. There’s no tag in the rear end. Any idea what the gear ratio is hot this truck?
     
  2. 77 K20

    77 K20 Supporting Member Supporting Member

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    Truck Year:
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    Truck Model:
    K20 5" lift
    Engine Size:
    HT383 fuel injected
    FYI- C10 would be a 2wd
    K10 would be a 4wd

    Is there any sort of sticker in your glove box? If it is there then it will either say or have a code for it.

    3.73s were popular.

    Otherwise you can jack up the rear end, put it in neutral and observe the ratio of the driveshaft turning compared to the tires.

    Welcome!
     
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  3. Charlie

    Charlie Full Access Member

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    Truck Year:
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    Truck Model:
    Cheyenne 10 LWB
    Engine Size:
    350/TH350/AC/4 BBL Quadrajet
    :welcome:
     
  4. Rickf

    Rickf Member

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    Pull the cover and count the teeth.
     
  5. Goldie Driver

    Goldie Driver Full Access Member

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    Location:
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    First Name:
    Britt
    Truck Year:
    1980
    Truck Model:
    GMC K1500 Suburban
    Engine Size:
    350
    I will guess 3.42's as that is what is in Goldie , my 80 K1500 Suburban .

    That's assuming the same TH350C auto tranny like mine, though .

    Good Luck!

    Britt
     
  6. 78C10BigTen

    78C10BigTen Full Access Member

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    Truck Year:
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    Truck Model:
    C10 BIG TEN
    Engine Size:
    350
    Easiest way to do it is jack it up, pull the cover, rotate wheels till the numbers on the ring gear come to you then find the digits and divide them.
     
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  7. 78C10BigTen

    78C10BigTen Full Access Member

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    Engine Size:
    350
    These numbers here. In this case, 43÷14=3.07

    2019-04-22 11.04.57.jpg
     
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  8. Arlo

    Arlo Junior Member

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    Truck Year:
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    Truck Model:
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    Engine Size:
    Still Debating
    3.07 Gear
     
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  9. roundhouse

    roundhouse Full Access Member

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    Truck Year:
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    Truck Model:
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    Engine Size:
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    Could be any thing
    I’ve seen 3.07
    3.73
    4.11
    4.56

    Only way to know is pull the cover and count the teeth or find the number stamp

    You need to change the oil and inspect the diff anyway
     
  10. HotRodPC

    HotRodPC Administrator Staff Member

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    6.2 to Gas???
  11. Craig 85

    Craig 85 Full Access Member

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    Truck Year:
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    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    My California smog '79 K15 had 3.07's.
     
  12. rpcraft

    rpcraft Full Access Member

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    3.07 was probably one of the more popular gear ratio's put in the 4wd trucks that came with a TH350. They did put some higher numbers of 3.73's in the 700r4 trucks but 3.07's were still more popular by a wide margin. If you are doing maintenance you should plan on changing the rear diff fluid, so you might as well get you some replacement gear oil and a gasket for each diff, plus some RTV, and have at it. While in there you can spin the diff around, check out the numbers, do the math, and also determine if you have an open diff or whatever going on in there. There's really no way to tell without actually seeing the gears at this point. EVen if you had the RPO code's and other info a previous owner could have changed the gears out.
     

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