Guess on gears in a '74 318 Duster with 8-1/4 rear

Discussion in 'Transmission and Drivetrain Tech' started by DusterDaddy, Sep 12, 2017.

  1. DusterDaddy

    DusterDaddy sledgehammer mechanic FABO Gold Member

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    If you had to guess, what gears are in the bone stock rear in my 74 Duster?

    The car is a factory 318/904 car with a fresh mild build 318 and a stock 904 cleaned up with a shift kit in it.

    Sadly there was nonfender tag and the mice shredded the build sheet under the back seat.

    Trans has the stock Mopar high stall converter in it. Have not really driven the car on the street other than a spin around the block yet but I am getting close to that point. I'm wondering how it will behave...
    IMG_6877.JPG
     
    Last edited: Sep 12, 2017
  2. 540slant6

    540slant6 Mopar SB Ripper

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    Probably 2.76 or 2.94. Best case would be a 3.23 unless someone special ordered 3.55's.
     
  3. 451Cuda

    451Cuda Well-Known Member

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    Probably 2.94
     
  4. oldkimmer

    oldkimmer Well-Known Member

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    A couple that I had with 318s had 2.71s. Kim
     
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    • 451Cuda

      451Cuda Well-Known Member

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      If you still have it on the lift, just mark the inside of right rear tire and a point on the pinion yoke, rotate tire exactly once and count revolutions of yoke.
       
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      • DusterDaddy

        DusterDaddy sledgehammer mechanic FABO Gold Member

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        A friend advised I do the same. She is home now, but easy enough to jack her up. i could just put the trans in neutral and count the yoke revs with on full turn of the wheel right?

        There are many mysteries within this nice little 318 I bought carb to pan. The builder is unknown but it has a purple cam with a .480 lift. That all I know about the cam. The motor lopes really nice at idle. The seller of the motor suggested I stay with the stock "high stall" torque converter so I did.

        The seller was a speed shop owner who acquired the motor, which was not fired until it was in my car, when he swapped it out of a Demon that one of his clients bought from a divorce situation. His shop kept the 318 as part of the compensation.

        It has Keith Black pistons and the interesting thing is the heads are stock 74 318 heads but they have the 360 1.88/1.60 valves in them and they are very nicely gasket matched and blended.
        It has a performer
        Intake and a 600 cam Holley street avenger on with with 340 hi-po exhaust manifolds and straight 2-1/2 duals.

        I look at it this way. I like that my car left the factory a 318/904 car and it still is a 318/904 car. It just has some
        Performance enhancements.

        My 69 318 bone stock 2 bbl barracuda would blow the doors off most anything off the line. So this thing should be a hoot to cruise around in....
        IMG_7555.JPG
         
      • H22A4

        H22A4 Well-Known Member

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        I'd guess 2.94 but if you might be super lucky and have 3.21's. 3.23 gears came in the 8 3/4, never in the 8 1/4.
         
      • SGBARRACUDA

        SGBARRACUDA ROY FABO Gold Member

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        I'll guess 2.45's
         
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        • SGBARRACUDA

          SGBARRACUDA ROY FABO Gold Member

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          Why not drop the rear cover and get right to the bottom of this mystery?
           
        • forphorty

          forphorty Well-Known Member

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          I've had two A body 8.25s and they were both 2.45s. Maybe I was just unlucky.
           
        • 318willrun

          318willrun Stomper 4x4... we kept energizer in business FABO Gold Member

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          my '76 8 1/4 has 2.45
           
        • 66jim

          66jim Well-Known Member

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          Had a 73 Dart Sport 318 904 I bought for he 8 1/4 from a local junkman, I wanted it to have 2.71 but to
          my surprise it was 3.21.
           
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          • halifaxhops

            halifaxhops 1st Unofficial instigator FABO Gold Member

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            I had 3.21 in a 74 dart but it also has the tow package.
             
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            • thesiren74

              thesiren74 Well-Known Member

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              Mine had 2.45s open.
               
            • DusterDaddy

              DusterDaddy sledgehammer mechanic FABO Gold Member

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              It would be like hitting the lottery if the gears are 3.21
               
            • DusterDaddy

              DusterDaddy sledgehammer mechanic FABO Gold Member

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              Cause whatever they are they are for now. Ill do 451cuda's test and get an idea of what I have for now..
               
            • Dartswinger70

              Dartswinger70 Well-Known Member

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              I think you can mark the driveshaft with chalk and count how many times it "goes around" to one turn of the tire or vice versa.
               
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              • DusterDaddy

                DusterDaddy sledgehammer mechanic FABO Gold Member

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                This is friggin bizarre!
                Jacked up the rear, car in neutral, rotated right rear wheel 1 full revolution. Driveshaft turned 1-1/8 full rotation.
                WTF?
                 
              • SGBARRACUDA

                SGBARRACUDA ROY FABO Gold Member

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                That is because your rear end is a open differential. That method works on SG rears. What you are encountering is the spider gears turning.
                 
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                • DusterDaddy

                  DusterDaddy sledgehammer mechanic FABO Gold Member

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                  I find new ways to embarrass myself each day...
                  Well over the winter we will need to get us some gears...
                   
                • 318willrun

                  318willrun Stomper 4x4... we kept energizer in business FABO Gold Member

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                  Ummm.... you could just pop the back cover off and read it.... :)
                   
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                  • TrailBeast

                    TrailBeast Slightly Twisted Member

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                    Taller gears ain't all bad either if you have the torque to pull em.
                     
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                    • DusterDaddy

                      DusterDaddy sledgehammer mechanic FABO Gold Member

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                      It stays as is for now. I'll take the cover off in January. lol
                      My car needs plenty of other things done before I take a perfectly working resr and give it a makeover.
                       
                    • DusterDaddy

                      DusterDaddy sledgehammer mechanic FABO Gold Member

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                      You're not the first guy to say that Trailbeast.
                      The whole project has been an adventure.
                      The last major thing left is to reset timing after discovering a leaky brake booster then I'll drive it a bit and go from there.
                      Ignorance, desire and determination are a productive combination, although I'm at this thing for nearly six years....
                      IMG_7558.JPG IMG_7547.JPG
                       
                    • TrailBeast

                      TrailBeast Slightly Twisted Member

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                      I hear ya, as my car was almost in that condition when I bought it and drove it home 150 miles without knowing anything about it.
                      I did notice it shifted from 1st straight to third right away, and that almost literally everything was either loose or broken.
                      Heck after I got the car home I found out all the spark plugs were only finger tight.:D