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best 10 Bolt gears for highway and low end torque

Discussion in 'Differential & Driveline' started by Evan, Sep 24, 2020.

  1. Evan

    Evan Junior Member

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    [​IMG]
    Hi i have a 1986 K10 with a SM465 four speed with a 205 Tcase and a 10 bolt rear end not sure what rear end gears i should use would like to cruise on the highway without the engine screaming but would like a little take off power also if anyone could guide me in the right direction that would be great thank you.
     
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  2. skysurfer

    skysurfer Full Access Member

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    What gears are in it now? I assume you are aware you have to do both ends, so your budget needs to be ready for that. Last issue is wanting low rpm on the highway but acceleration off the line. There’s no magic gear ratio that will get you both, so decide what’s more important.
     
  3. Evan

    Evan Junior Member

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    I'm in the process of fixing the truck up and swapping in the transmission not sure what's in it right now yet but it has a th350 auto in it at the moment and at 55 the engine is around 3000 rpm. I know the SM465 is geared pretty low so i guess i would like to be able to get my rpms down on the highway
     
  4. Swearbody

    Swearbody Supporting Member Supporting Member

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    id say swap i the 465 and see what you get. The first gear is like 6.55:1 compared to the th350 being around 2.65:1. you will get a huge difference in take off from that big of a difference alone. The jump will be pretty drastic from 1-2 regardless in a 465.

    So 55 @3000rpm with what look to be 33ish tires id say your gears are already pretty low...like 4.10 or lower
    with that 465 youll be able to pull a house.
    Hell 2nd gear is lower than a th350 or even a 700r4 and 4th is 1:1
    With the 1:1 4th youll be at the same speed that your th350 is at on hwy since the th350 3rd is 1:1 so keep that in mind. You may end up wanting taller gears unless you plan to pull a HEAVY trailer.
     
  5. Swearbody

    Swearbody Supporting Member Supporting Member

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    All of that is hinged on the 10bolt holding up to the torque of a 6.55:1 reduction and your low gearing in the first place. Id be suspect on that lasting too long with any real power being applied.
     
  6. BKING33

    BKING33 Full Access Member

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    3.73 is a good starting point. Any higher than that and you will lose all your torque pulling on highway
     
  7. Swearbody

    Swearbody Supporting Member Supporting Member

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    I like the truck though. Looks good. Ive wanted a duckbill(over cab cowl) for mine a while now
     
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  8. Frankenchevy

    Frankenchevy Lying Dog-Faced Pony Soldier Supporting Member

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    3.73 with a 33” tire at 1:1 will be a touch under 2600rpm. The sm465 will be barely lower rpms only because the th350 is never locked up.
     
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  9. Grit dog

    Grit dog Full Access Member

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    Makes me want to keep mine after I repaint the truck! Truck looks great!
     
  10. Grit dog

    Grit dog Full Access Member

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    Beautiful truck btw.
    1st is basically a granny gear in a 465, so theoretically off the line, you're already part way through 2nd gear in a 465 at 1st gear ratio in a Turbo350. That said, if you would want to use 1st gear all the time, gear it up where 4th is basically an over drive for you. 3.08, 3.23, 3.42 tops.
    3000rpms at actual 55mph is fckin low geared 4.56 min, maybe deeper.
    My truck is 4.10s, 1:1 (turbo 400), 35s which are half worn out and a little short for their size so closer to a new 33" tire and 3000rpms is 69-70mph on gps (speedo reads about 10mph slow, presume your trans has the right speedo gear for the tires or gps verified?)
    3.73s are right in the middle. Generally the balance point between power and rpms.
     
  11. rpcraft

    rpcraft Full Access Member

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    Hate to be that guy but have you looked at going with a nv4500 or a 700r4? Might make your current gears perfect and to be honest its easier to swap a transmission in to test than gears and be wrong...
     
  12. Grit dog

    Grit dog Full Access Member

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    ^ Or sticking with a period correct 4 speed, if you can find a NP833 4 speed, you’ll lose granny gear and gain a respectable OD gear.
    Cost? Flip a coin probably compared to re gear.
     
  13. Grit dog

    Grit dog Full Access Member

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    But first figure out what gears you have in it.
    That literally takes 5 min driving with gps and measuring your tire diameter. Then use an online calculator if you can’t do the math.
    What you’re saying equates to 4.88s giver take 1 size which is extremely low for a street driven truck with smallish tires like you have.
    Also very nice to have those gears and I’d rather add OD and keep the stump pulled gears if they’re in good shape.
     
  14. Evan

    Evan Junior Member

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    Ok i will have to figure out the gears in it right now i might get the sm465 in and see what i have and then go from there. This is my first project im taking on by myself so all of this information is very appreciated. I also thought about a NV4500 but i already have a sm465 purchased and ready to go in.
     
  15. rpcraft

    rpcraft Full Access Member

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    I would honestly figure it out before you swap anything. Did someone own this truck before you and have big tires on it? (LIKE REALLY BIG, MAYBE 44'S OR SOMETHING...)
     

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