1. 70 DDDart

    70 DDDart Member

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    I am running 255 x 60-15" BFG's on rear with 391 SG gears with A 833 4 speed. My FSM chart does not list P- metric sizing because it is for 1971 cars. There is not enough reliable info on the internet to convert the tire size. It looks like a 39 tooth gear should be close to correct my speedometer so does anyone have real experience so I can dial this in. Classic lists all gears but at $60 a pop I like to get this right the first time?

    Also the FSM lists two A-833 trannie's a "Standard" and a "Heavy Duty", slight difference in 1 st and reverse ratio's and also lube capacity. How do you tell the difference without a dismantle? My trans has a 1" x 23 spline input shaft, if that helps.
     
  2. Professor Fate

    Professor Fate Push the button, Max...

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    BFG lists your tire as having an overall diameter of 27.1", so using this chart: Mopar Speedo Gear Chart : Drivin' It Home you need a 38 tooth gear, which translates to 2538938(Blue).
    The FSM covers Darts, Coronets and Chargers, so the "standard" 833 is the 23 spline, and the "Heavy Duty" is the 18 spline Hemi/6bbl box. The capacity difference is due to the A body vs. B body boxes, which have different length tailshaft housings.
     
  3. toolmanmike

    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    255 60-15's are 27" tall. I think the standard transmissions came in pretty much everything except the 13 spline tht was used in the Hemi's and 440-6 cars.
     
  4. toolmanmike

    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    Looks like you need a 38 tooth.

    speedo gear.jpg
     
  5. Alaskan_TA

    Alaskan_TA Well-Known Member

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    Just for use in the future, with your tire inflated to the proper PSI you can measure the diameter yourself. ;-)
     
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    • 70 DDDart

      70 DDDart Member

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      Thx all 3 of you, I will be looking now to try and get a better price for a 38 tooth gear than from Classic !!!!
       
    • toolmanmike

      toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    • 69cudaownr

      69cudaownr FABO Gold Member FABO Gold Member

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    • toolmanmike

      toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    • dibbons

      dibbons FABO Gold Member FABO Gold Member

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      You might want to add a GPS speedometer to your smart phone and get some good numbers driving down on the highway (at different speeds) to determine how your GPS speed reads now (compared to the dash speedometer) to get an accurate baseline on how far off you are and go from there.
       
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      • toolmanmike

        toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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        Great idea. GPS is usually accurate to within 1 mph or less. Try Waze.
         
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