How to identify if a transmission is double OD

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by mile marker 27, Jun 17, 2022.

  1. mile marker 27

    mile marker 27 Road Train Member

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    I’ve got a 15 against the dash in my 379 Pete dump truck. I think it’s got 4:25 rears but I’m gonna bet it’ll run over 100. I bought it back in December, from north central KS and drove it back to Joplin Mo for the night. In the first hour I could see the old truck was gonna do fine and then I decided to air it out. Drove it around 85-90mph for hundreds of miles. I’ve seen and read discussions on hear about the OD’s/ DOD’s and the fact that the gears being flipped, doesn’t always mean it’s a DOD. Explain and let me know how to identify.
     
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  3. roundhouse

    roundhouse Road Train Member

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    Does the trans have a data plate ?
    Figuring the axle gearing is easy.
    Jack up , get both wheels off the ground .
    Make a chalk mark on the wheel and one in the driveshaft .
    Turn the wheel and count the rotations of the shaft .
     
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  4. baha

    baha Road Train Member

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    That's why most have the deep reduction lower gears, so when you are loaded and pointed up a hill you can still get it moving and most have the .73 over drive? A 10 speed with the back box flipped around won't get started loaded on any kind of hill! But will get you a speeding ticket with out trying hard.
     
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  5. AModelCat

    AModelCat Road Train Member

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    Need the model number. You could get an overdrive 15 with the stick against the dash or towards the back wall. All depends on the top cover.
     
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  6. jamespmack

    jamespmack Road Train Member

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    Pretty certain no 15 speed eaton was avaliable with 2 overdrive gears. Single od only.
     
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  7. AModelCat

    AModelCat Road Train Member

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    I'm thinking you're probably correct. OD in the main box, deep reduction, low range and high range (direct) in the back box.

    At least that's how mine is.
     
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  8. mile marker 27

    mile marker 27 Road Train Member

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    .......so the only thing with double OD’s would have been a 13?
     
  9. jamespmack

    jamespmack Road Train Member

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    Just to be clear, I have about zero experience with a 8ll or 15 speed.

    Eaton Rtoo,Rtlo would be only double overdrive trans I'm aware of. 13,or18 speeds.

    Maybe be others, will need someone else to answer that.
     
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  10. SmallPackage

    SmallPackage Road Train Member

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    No 15 double O’s from Eaton factory but a 15 can be modified to be double o by the right shop. Has been done many times but they can be very noisy on the top end. More so then the old 9513’s that howl in od around 60-65 mph.
     
  11. jamespmack

    jamespmack Road Train Member

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    Had a 9513 all new parts, in 9th od overdrive rear sound like a bucket of bolts. Quiet in every other gear. Straight cut gears are loud!


    I feel I have heard that. But would it not be huge ratio jumps?
     
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