Speedometer Pinion Gears help need again.

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    Author Topic: Speedometer Pinion Gears help need again.  (Read 6184 times)

    Offline widing'cuda

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    Speedometer Pinion Gears help need again.
    « on: August 30, 2007 - 05:16:51 PM »
    Here's the fact I know.
    I have 255/60/15 rear tires that's 27" tall. The speedometer pinion gear in the 'cuda is 34 teeth.
    The speedo shows that I'm doing 80 mph when I'm actually 50 mph.
    I have 2000 rpm when I'm doing 50 mph, so I think I have a 3.23 rear end, but I'm not sure.
    How many teeth should it be on the speedometer pinion gear?
    « Last Edit: August 30, 2007 - 05:47:01 PM by widing'cuda »
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    - Jørgen - Norwegian Mopar fanatic

    1970 Plymouth 'Cuda 383 A833 8-3/4 3.23 suregrip
    http://cuda.widing.biz/


    Offline MEK-Dangerfield

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    Re: Speedometer Pinion Gears help need again.
    « Reply #1 on: August 30, 2007 - 06:24:26 PM »
    I have the same rear tires as you do. I have 3:23's. I also a green 34 tooth gear, and it's dead on.  :grinyes:

    What you are saying doesn't make sense to me. I originally had a 26 tooth gear(red) that would give me 80MPH at 60. 2000RPM at 50MPH sounds right for 3:23's and those tires.  :clueless:  Are you SURE the gear is 34 teeth? There are other green gears too.

      Mike
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    Mike

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    Offline Bullitt-

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    Re: Speedometer Pinion Gears help need again.
    « Reply #2 on: August 30, 2007 - 07:05:48 PM »
    The handy dandy calculator says a 31 tooth would be correct, still need to be very sure of the rear ratio.
    http://www.moparts.com/Tech/tech/img/AUTOMATICchart.xls
    http://www.moparts.com/Tech/tech/img/4SPEEDchart.xls

    not sure which tranny you have but I played with the ratios on an automatic & at 2000rpm/50mph a 2:95 ratio would be more like it.....which wants a 27 tooth speedo gear.
    « Last Edit: August 30, 2007 - 07:10:02 PM by bullitt99 »
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
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    Offline widing'cuda

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    Re: Speedometer Pinion Gears help need again.
    « Reply #3 on: September 01, 2007 - 03:51:59 PM »
    I counted the teeth on the gear before i installed it. And it is a 34. The one I took out was 33 teeth gear (black). And it show that i was doing 100 mph when I was really doing 62 mph when I had a 275/60/15 rear tire (28" tire).

    My tranny is a 727 that is # matching to the 'cuda. The wheel I have on is 27" tall and at 2000rpm I'm doing 49.71 mph. Calculated from 80 km ph, as kph what regular cars use here in Norway. But I regular car can be of by 5 kph.

    I leaning towards that something has been done to  my speedo at some time to convert to kph.
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    - Jørgen - Norwegian Mopar fanatic

    1970 Plymouth 'Cuda 383 A833 8-3/4 3.23 suregrip
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    Offline ted

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    Re: Speedometer Pinion Gears help need again.
    « Reply #4 on: September 01, 2007 - 04:34:40 PM »
    stop guessing, unless you know the gears ratio  thats all you r doing.

    Quote from: widing'cuda on August 30, 2007 - 05:16:51 PM
    Here's the fact I know.
    I have 255/60/15 rear tires that's 27" tall. The speedometer pinion gear in the 'cuda is 34 teeth.
    The speedo shows that I'm doing 80 mph when I'm actually 50 mph.
    I have 2000 rpm when I'm doing 50 mph, so I think I have a 3.23 rear end, but I'm not sure.
    How many teeth should it be on the speedometer pinion gear?
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    74 cuda, 70 challenger r/t

    Offline widing'cuda

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    Re: Speedometer Pinion Gears help need again.
    « Reply #5 on: September 01, 2007 - 04:41:32 PM »
    Quote from: ted on September 01, 2007 - 04:34:40 PM
    stop guessing, unless you know the gears ratio  thats all you r doing.


    How do I check the rear end radios then?
    Jack up the car. Turn the wheel and count how many time the drive shaft turns?
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    - Jørgen - Norwegian Mopar fanatic

    1970 Plymouth 'Cuda 383 A833 8-3/4 3.23 suregrip
    http://cuda.widing.biz/

    Offline Bullitt-

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    Re: Speedometer Pinion Gears help need again.
    « Reply #6 on: September 01, 2007 - 04:52:31 PM »
    Here are the possible gear ratios for a 8 3/4" 2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17, 5.57. ...
    with the calulator http://www.moparts.com/Tech/tech/img/AUTOMATICchart.xls
    input your known data & a gear ratio, change the ratio to see where the RPM vs. Speed match your car, then get the speedo pinion closest to the result.
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
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    Offline widing'cuda

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    Re: Speedometer Pinion Gears help need again.
    « Reply #7 on: September 01, 2007 - 05:16:16 PM »
    Quote from: bullitt99 on September 01, 2007 - 04:52:31 PM
    Here are the possible gear ratios for a 8 3/4" 2.76, 2.93, 3.23, 3.31, 3.55, 3.73, 3.91, 4.10, 4.56, 4.89, 5.17, 5.57. ...
    with the calulator http://www.moparts.com/Tech/tech/img/AUTOMATICchart.xls
    input your known data & a gear ratio, change the ratio to see where the RPM vs. Speed match your car, then get the speedo pinion closest to the result.


    I have a 8-3/4 742 housing on my 'cuda. And according to the xl file I have a 2.94:1 rear end gear.
    As 2000 rpm in 3rd gear with a 255/60-15 wheel is 51 mph. So I need a 28 teeth gear.
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    - Jørgen - Norwegian Mopar fanatic

    1970 Plymouth 'Cuda 383 A833 8-3/4 3.23 suregrip
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    Offline MEK-Dangerfield

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    Re: Speedometer Pinion Gears help need again.
    « Reply #8 on: September 01, 2007 - 06:00:00 PM »
    If your speedometer is reading too fast, you need a gear with more teeth. If 34 doesn't work for you, then 28 is going in the wrong direction.


      Mike
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    Mike

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    Offline Bullitt-

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    Re: Speedometer Pinion Gears help need again.
    « Reply #9 on: September 01, 2007 - 06:03:04 PM »
    Quote from: widing'cuda on September 01, 2007 - 05:16:16 PM
    I have a 8-3/4 742 housing on my 'cuda. And according to the xl file I have a 2.94:1 rear end gear.
    As 2000 rpm in 3rd gear with a 255/60-15 wheel is 51 mph. So I need a 28 teeth gear.
    that's what I get with the same parameters.
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
    Screwed by Photobucket!

    Offline Bullitt-

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    Re: Speedometer Pinion Gears help need again.
    « Reply #10 on: September 01, 2007 - 06:04:26 PM »
    Quote from: MEK-Dangerfield on September 01, 2007 - 06:00:00 PM
    If your speedometer is reading too fast, you need a gear with more teeth. If 34 doesn't work for you, then 28 is going in the wrong direction.


      Mike
    mike, Just going by the calculator that is not necessarily how it works
    Wade
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
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    Offline Bullitt-

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    Re: Speedometer Pinion Gears help need again.
    « Reply #11 on: September 01, 2007 - 06:12:23 PM »
    her's a chart that back up the calulators findings.
    AXLE RATIO                 tire height
                24"         26"        28      30"
    2.76 2538930 2538928 2538926 2538924
    2.94 2538932 2538930 2538928 2538926
    3.21 2538935 2538933 2838931 2838929
    3.55 2538939 2538936 2538933 2538931
    3.91 2538943 2538940 2538937 2538935
    4.10 2538945 2538942 2538939 2538936
    4.30  2538944 2538941 2538938
    4.56  2538945 2538943 2538940


    Please note: these numbers are for the standard style pinion gear
    also last two numbers are the number of teeth, 2538945 = 45 teeth
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
    Screwed by Photobucket!

    Offline MEK-Dangerfield

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    Re: Speedometer Pinion Gears help need again.
    « Reply #12 on: September 02, 2007 - 04:29:32 AM »
    Quote from: bullitt99 on September 01, 2007 - 06:04:26 PM
    mike, Just going by the calculator that is not necessarily how it works
    Wade

    Going by his original statement, I just have a feeling he is wrong about what gears he has in the rear. That's why I said he needed a gear with more teeth. There is NO way a 34 tooth gear can be that far off if he has 3:23's, and 27" tires. I guess we'll get to the bottom of this eventually.


      Mike
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    Mike

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    Offline Bullitt-

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    Re: Speedometer Pinion Gears help need again.
    « Reply #13 on: September 02, 2007 - 10:16:02 AM »
    Quote from: MEK-Dangerfield on September 02, 2007 - 04:29:32 AM
    Going by his original statement, I just have a feeling he is wrong about what gears he has in the rear. That's why I said he needed a gear with more teeth. There is NO way a 34 tooth gear can be that far off if he has 3:23's, and 27" tires. I guess we'll get to the bottom of this eventually.


      Mike

    Mike, there are some things we average mortals are not meant to understand, I have come to the conclusions that speedo pinion gears are one of them....give into the force so to speak.
    Use the calcuator Luke 
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    Wade  73 Rallye 340..'77 Millennium Falcon...13 R/T Classic   Huntsville, AL
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    Offline widing'cuda

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    Re: Speedometer Pinion Gears help need again.
    « Reply #14 on: September 02, 2007 - 12:42:40 PM »
    I'll jack up the 'cuda tonight. Have my girlfriend turn the wheel. And I'll be counting how many time the drive shaft turns. That way I should know. Just about what kind of rear end radios I have on the 'cuda.
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    - Jørgen - Norwegian Mopar fanatic

    1970 Plymouth 'Cuda 383 A833 8-3/4 3.23 suregrip
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