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Auto doubler vs manual doubler

Discussion in 'OffRoad Design' started by TopOff, Mar 21, 2002.

  1. TopOff

    TopOff 1/2 ton status

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    Curious about the ratios for rack crawling.

    I am under the impression that a manual with deeper gears will be better for rock crawling. I am looking at a TH400 (or TH350) 203/205 vs a sm465/203/205.
    So without the differential gears - the TH400 would be about a 2.8x4 = 11:1 where as the sm465 will be about 6.50X4 - 26:1 right?

    Anyone say something to the contrary regarding rock crawling?

    TIA
    TO
     
  2. Greg72

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

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    TopOff,

    Auto trannies will give you an additional 2:1 ratio to factor into your calculations.....it is because of the "slipping" of the torque converter at low RPMs.....

    So if you thought your crawl ratio was 11:1.....it's probably more like 22:1

    There are some good discussions about this effect either on the "ORD board" or the "'73-'91 board" archives. There were also a couple of good articles in the 4x4 mags about calculating crawl ratios where they went into detail about the "auto-tranny 2:1 crawl effect"

    So it's not as 1-sided of a comparison as you thought......(stick isn't necessarily THAT much "crawlier"!! /forums/images/icons/laugh.gif)
     
  3. 72THING

    72THING 1/2 ton status

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    I agree with Greg72. The additional torque multiplication of an automatic can really make up for the lack of lower gears in an auto. The slippage of the torque converter can usually be considered about 2:1, even though it can be lower than that at times. I prefer a manual just because I like to shift gears, but there's been plenty of times when i thought, " Man it would be nice to have an automatic." You can just finesse the gas pedal to ease over an obstacle instead of fumbling with slipping the clutch. It really boils down to a matter of personal preference.

    Auto Pros: torque multiplication effect, not having to shift, fast gear changing, no clutch to burn out.
    Auto Cons: More complicated (more to go wrong), needs a cooler for reliable offroad performance, possible cavitation at extreme angles, longer front driveshaft when using doubler.

    Manual Pros: getting to shift gears, bulletproof, needs no cooler, bulletproof, no risk of fluid cavitation at extreme angles, bulletproof, less to go wrong.
    Manual Cons: SM465 not a fast shifting tranny, non-synchronized first gear=lots of gear grinding, straight transmission of power means you have to slip the clutch to get the torque multiplication effect, clutch burning, short front driveshaft when using doubler.
    Hope this helps.

    Will
     
  4. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    Much debate over that one, the searches will find good info.
    I personally prefer an auto. They do behave a little different but practically speaking a Doubler with an auto and and a Doubler with a manual are going to be equivalent in trail performance.

    I usually say drive what you like.
     
  5. TopOff

    TopOff 1/2 ton status

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    Did the search thing, I haven't found much... I will try again.

    Thanks
    TO
     
  6. Greg72

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

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