tranny pinion
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Thread: tranny pinion

  1. #1
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    tranny pinion

    Got a question for the tranny gurus out there, I took the 68 on it maiden voyage and by god, it moves 0/. One thing I did noticed was that the speedo was reading faster than what it should be, even though I don't know how much faster, it is obvious that I was not going that fast. I have a 32 spline pinion gear and unless I'm reading the book wrong I don't know what it should be. I'm running a 727 and 3.23 gears, the tires are 235/60/14 approximately 25 1/2" tall, any ideas? Thank you guys!

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  3. #2
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    Re: tranny pinion

    This is from the Mancini Racing web site. If you give them a call, I'll bet they can fix you up with the right gear. Willie Product Description
    A lot of us choose to change tires size on our cars and trucks as one of the modifications we do to make it our own personalized rigs. We will also swap out the rear end gears to make it run the way we like. By making one or both of these changes the speedometer is thrown off.

    The 1 mile on the speedometer is equal to 1000 turns of the speedometer cable. The out put shaft on all mopars from 1964 and up has 13 teeth on it. The following formula will give you the number of teeth you need on the speedometer pinion gear to make the speedometer read the proper miles per hour.

    Please Note: These part numbers are for the standard style pinion gear.

    Here is an example on how to calculate the wheel diameter to select a speedometer gear to use with the desired ring/pinion gear.

    Tire Size: 245/60/15

    245mm/25.4mm = 9.64 Inches Section Width

    9.64 in. X 60% = 5.79 in. Side Wall Thickness

    5.79 in. X 2 = 11.57 in. Total Side wall height

    11.57 in. + 15 in. (Rim Size) = 26.6 in. Diameter

    So with this Tire Size and 3.91 Gears, I would use a 40 Tooth Speedometer gear.
    383 bored .030, Stage IV iron heads ported with MP templates. 11. to 1 comp. MP .528 mech. cam. Holley TBI. TF-727 w/B&M 10" 3000 stall conv. 8. 3/4" w/4.10 suregrip, moser axles.

  4. #3
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    Re: tranny pinion

    Wilsd383, thank you for the reply, that is very interesting, I will give them a call.

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  6. #4
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    Re: tranny pinion

    This is not too scientific, but usually your are very close to the gear ratio.
    example: 3.23 = 32 or 33, 3.55 = 35 to 36 My 3.73 woth 29" tire was around a 36 tooth,
    I had a 4.10 before with a 40 tooth. 1 tooth is about 5mph.
    Rick
    2014 Ram 1500 Eco Diesel - Daily driver, Hauler

    1979 Jeep Cherokee Chief - Gen 3 Hemi- Turbocharged, running E85, 1 ton axles,
    4.56 gear on 38" tires - Toy in progress

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