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Gears... huh?

Discussion in 'The Garage' started by mike2891, Jul 24, 2005.

  1. mike2891

    mike2891 Registered Member

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    At the risk of sounding like a complete moron, i'm going to ask anyways. I'm relatively new to working on 4wd's and building them up.. and I somewhat understand the whole idea of the gear ratio's and whatnot... but honestly I really don't get it all.... I have an 88 blazer how do I know what gears it has & how big of tires I can go without changing a bunch of stuff? Any place I can readup on this stuff? Basically I'm teaching myself everything as I go & I have to honestly say I just don't get it... so any info would be greatly appreciated!!
     
  2. tarussell

    tarussell 1/2 ton status

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    To offer a fairly basic answer , and to help you understand a little better , think of gear ratio's this way .
    The engine turns one full turn than the tranny turns ( I am assuming you have an automatic tranny ) 3.06 times slower.Than the transfer case turns ( assuming low range is selected ) 2.61 times slower,as the driveshft turns the pinion the pinion turns the ring gear and that will be what ever your ring and pinion ratio is ( lets say it is a 3.73 gear ) . The ring gear will turn the differential and the differential turns the axles slower which turn your tires - the differential turns 3.73 slower than the pinion does.
    All the reduction added up together is your crawl ratio.
    Gear reduction is turning slower than the crank shaft and gear overdrive is turning faster than the crankshaft , while a one to one ratio is turning at the same speed as the crankshaft.
    There are factors to consider such as torque converter slip but I am just trying to be very basic so it will be easier to grasp.
    HTH , Tom

    I edited this with the words "slower" to be a little clearer with what I am saying - sorry for any confusion . Sometimes the written word is difficult to get from my head to typed words.
     
    Last edited: Jul 24, 2005
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Maybe I misread that, but I think you have all of that backwards. Diff ratio of 3.73 means the engine is turning 3.73 times the ring gear speed. Low range of 2.61 means it's now turning 3.73x2.61 (9.73) times faster than the ring gear. 3.06:1 tranny ratio means it's now turning 9.93 x 3.06 (29.79) times faster than the ring gear. This would all be without factoring in TC voodoo.

    Rene
     
  4. tarussell

    tarussell 1/2 ton status

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    It all depends on how you look at the power flow . From the axle point of view the engine is turning faster but from the enging point of view the axles are turning slower. It all depends on which way you look at it.
    Tom

    EDIT : I guess I am not as clear as I think I am when I type Ha ,ha I don't mean to say that the reduction is faster but rather the gear reduction turns slower than the driven force which is the crankshaft.
    Tom
     
    Last edited: Jul 25, 2005
  5. loafer

    loafer 1/2 ton status

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