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TH350 - ??What gear is it??

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Greg72, Mar 19, 2001.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I'll admit, I'm a little lost here. I was trying to calculate some basic stuff on engine RPMs and Tire Diameters, and pretty much the first thing you need for the formulas is the gear ratio. That should be the combination of the (individual gear ratio X rear end gear).

    I know I have a stock TH350 tranny, and I have 3.73 gears....What I don't know is, what are the stock gears in that transmission? Anybody know? I have a few documents with basic K5 dimensions and capacities, but nothing on the gear ratios.

    Thanks,

    -Greg72
     
  2. Roostr84

    Roostr84 1/2 ton status

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    Not sure what yor after but most rpm tire ratio formulas look for final drive which is 1:1 in a th350. But you have to factor in a few hundred rpm for converter slippage too.
     
  3. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I guess I'm comparing it to manual transmissions which is my only area of familiarity

    Suppose you have a transmission with the following gears:

    1st 3.08:1
    2nd 2.45:1
    3rd 1.48:1
    4th 1.14:1
    5th .89:1

    And a rear end ratio of 4.10:1

    To calculate a MPH, you need to multiply the individual gear ratio by the final drive to get a "mulitplication factor"

    ex. 3rd Gear (1.48) x Rear End Ratio (4.10) = Multiplication Factor of 6.068.....that's the number that gets plugged into the formulas for MPH or RPM, etc.

    (NOTE: All the ratios in the example are made up. I'm not trying to say those are actual ones for any K5) ;^)

    If this make sense to anyone.....and you can help bridge the "gap" in my knowledge please jump in here!


    Thanks again,

    -Greg72
     
  4. 71RestoRod

    71RestoRod 1/2 ton status

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    The gearing on the TH350 is: 1st:2.52, 2nd:1.52 and 3rd:1.00. By the way, if you are comparing w/ a 700R4, those ratios are 1st:3.06, 2nd:1.62,3rd:1.00 and OD:0.70.

    Here is a link to Randy’s Ring & Pinion on-line calculators: <A target="_blank" HREF=http://www.ring-pinion.com/RPMCalculator.html>http://www.ring-pinion.com/RPMCalculator.html</A>
     
  5. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    AWESOME!! That's exactly what I was looking for!

    Thanks to you 71RestoRod!

    -Greg72
     
  6. Sledge

    Sledge Registered Member

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    Or if you're like me and doing a 4L80-E swap the ratios are:

    1st: 2.482
    2nd: 1.482
    3rd: 1.1
    4th: 0.75
     

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