Another 8 3/4 question

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    Author Topic: Another 8 3/4 question  (Read 2824 times)

    Offline 1BADFISH™

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    Re: Another 8 3/4 question
    « Reply #15 on: September 21, 2006 - 10:08:34 AM »
    Quote from: 360cuda on September 19, 2006 - 09:58:05 PM
    You could still find the gear ratio by spinning the rear tire and counting full driveshaft rotations.
    Block a front wheel, jack up the car so both rear wheels are off the ground and take the car out of gear

    Position a rear wheel with the valve stem at TDC and put a small piece of tape on the side of the driveshaft.
    More accurate when you spin the wheels all the way around twice.

    Spin the rear wheel 2 times and count the u-joint rotation. I look at the U-joint zerk fitting but you can just put a piece of tape on the driveshaft if mufflers are in the way
    6 1/2 times around is 3:23 gear.  7 count is 3:55.  almost 8 count is 3:90 ect

    Of course, you can only use this method if the suregrip is working  :burnout:



    Will this work with an open rear end? I am trying to get an estimate what my gear ratio is too, but I have an open rear end  :puke:  (for now)

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    Dave
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    2014 GMC Sierra Crew Cab White Diamond edition.
    1970 Dodge Challenger 340-6 4spd.
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    Offline Chryco Psycho

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    Re: Another 8 3/4 question
    « Reply #16 on: September 21, 2006 - 11:09:49 AM »
    if you jam one wheel it will double the wheel speed but it is still accurate
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    Offline 360 'CUDA

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    Re: Another 8 3/4 question
    « Reply #17 on: September 21, 2006 - 11:48:38 AM »
    Right!!

    With a non suregrip just jack up one side of the car, take it out of gear and spin the tire all the way around twice.
    Count the number of times the driveshaft spins but this time do not cut the number in half like the suregrip example.

    3 1/4 times is 3:23, 3 1/2 times is 3:55, almost 4 times is 3:90 ect

    Most likely it's a 3:23 but really it could be anything.  I have one that is 2:56  :2thumbs:
    The 8 1/4 in my Charger is 2:76 but the 440 spins the wheel just fine  :banghead:
    « Last Edit: September 21, 2006 - 11:50:45 AM by 360cuda »
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    Offline 1BADFISH™

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    Re: Another 8 3/4 question
    « Reply #18 on: September 21, 2006 - 12:14:29 PM »
    Quote from: 360cuda on September 21, 2006 - 11:48:38 AM
    Right!!

    With a non suregrip just jack up one side of the car, take it out of gear and spin the tire all the way around twice.
    Count the number of times the driveshaft spins but this time do not cut the number in half like the suregrip example.

    3 1/4 times is 3:23, 3 1/2 times is 3:55, almost 4 times is 3:90 ect

    Most likely it's a 3:23 but really it could be anything.  I have one that is 2:56  :2thumbs:
    The 8 1/4 in my Charger is 2:76 but the 440 spins the wheel just fine  :banghead:

    If thats the case I think I have a 2:56   :woo:   :banghead:
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    Dave
    Charlottetown, PE
    2014 GMC Sierra Crew Cab White Diamond edition.
    1970 Dodge Challenger 340-6 4spd.
    *Member Since* Oct 11, 2005

    Offline Jacksboys

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    Re: Another 8 3/4 question
    « Reply #19 on: September 21, 2006 - 12:27:06 PM »
    Quote from: BIGSHCLUNK on September 21, 2006 - 07:17:12 AM
    So are we equating this to a $.10 rear end?? This cars NOT that qwick off the line...  :clueless:

    Bigs,
    Since the car has the original tranny, it may have the original torque converter, which could be to low of a stall speed for your engine.  This would cause it to be a little slower off the line.  Just a thought.
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    Offline moper

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    Re: Another 8 3/4 question
    « Reply #20 on: September 27, 2006 - 10:12:21 AM »
    The easiest way is to drive with a known car's speedo, and get the right rpms. A factory tach in most cases is off a few hundred rpm, and the speedo I'm sure is off. So true rpm, tire size, and mph are what you need to know. My guess is it's a 3.23 or 3.55 gear, and the speedo and tach are off.
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