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Transmission Ranging

Discussion in 'Flat Fender Tech' started by oldtime, Jan 7, 2021.

  1. Jan 7, 2021
    oldtime

    oldtime oldtime

    St. Charles,...
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    As you may know I prefer to call the topic of various gear selections as “GEAR RANGING”.
    And gear ranging is a study closely related to “ENGINE RPM RANGING”.
    These then are the 2 main sciences used to define internal combustion engine velocity relative to vehicle motion.

    The engine always ranges from lowest rpm called “idle” to highest rpm called “redline”.
    The engine rpm producing maximum torque output is the most efficient velocity for any given engine.
    Given sufficient traction our speed will always be proportional to the engine rpm and gear selection.

    The overall gearing selection ranges from crawl speed to cruise speed.

    A LOW / CRAWL RATIO simply implies a slow speed and yes the exact speed is determined by engine rpm and tire diameter.
    The tire diameter simply quantifies the distance per final drive revolution.
    Slowing the foreward speed is mainly needed to provide more time for driver observations and actions.
    In my instance here I will be satisfied with a crawl ratio providing a usable “trail speed” somewhere between a 45/1 ratio and a 60/1 ratio.
    IMHO Anything slower than 60/1 ratio is only useful for log or rock crawling and perhaps engine braking.

    The CRUISE RATIO is configured to obtain ideal hiway speed at the velocity of maximum engine torque output.

    In my instance I am running a standard Dauntless engine and it’s rpm providing maximum torque output is 2400 rpm.
    So my cruise ratio is arranged so the Jeep is operating at 2400 rpm while traveling just above 60 mph on 32” tires.
    I will be running a low geared silent type D20 transfer case so overdrive is not an option in this scenario.
    Get out your gear calculators and you will see that I need 3.73 differential ratio to obtain 61 mph at 2400 rpm on 32” tires.
    So excluding the ever increasing wind drag this Jeep should have it’s most efficient use of fuel while operating at 61 mph.

    So now this particular Jeep ranges from 3.73 cruise ratio to a let’s say a 6O/1 crawl ratio.
    But wait there’s more...
    Here is where I am about to inject a few concepts concerning “transmission ranging”.

    To be continued.....
     
    Desertdog48, OldAdobe, dane71 and 2 others like this.
  2. Jan 7, 2021
    Norcal69

    Norcal69 Out of the box thinker 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Finally! Somebody puts my thoughts into the proper order and posts them up.
     
  3. Jan 7, 2021
    oldtime

    oldtime oldtime

    St. Charles,...
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    As previously stipulated the transmission will be fitted between a Dauntless 225 and the silent type Dana model 20.
    Because overdrive is not an option I want as many synchronized gear selections I can get.
    So my favorite transmissions concerning fitment are the various Borg Warner 4 speeds.
    And because the overdrive will not be an option I will use 3.73 differentials to effect proper cruise rpm / speed.

    In general via the manual transmission we are selecting from the various ratios to increase the engine torque and thereby control acceleration / deceleration.

    When accelerating from a dead stop we need a proper gear ratio providing adequate acceleration and a sufficient parking lot speed.
    I usually refer to the appropriate gear as the “street low” or the “take off” ratio.

    I absolutely love the 15/1 1st gear ratio that Jeep used as their time proven standard from 1945 cj to mid year 1963.
    Even after 1963 the CJ street low ratio only slightly sped up to 14/1 prior to the Dauntless CJ with its 3.73 differentials.
    So my goal here is to stay in to he realm of 14/1 or 15/1 fully synchronized street low ratio and not much if any faster nor slower.

    Regardless the street low ideally will be fully synchronized, so we can illegally roll slowly past the stop sign.

    A word of CAUTION! ... no one was anywhere near that stop sign that we just rolled past excepting Roscoe P Coaltrain who was hiding behind a billboard.

    So here’s where I propose as many others have done before, the Ford Borg Warner T19.
    As you know 3 fully synchronized version were available.
    4.02 Narrow Ratio
    5.11 Wide Ratio
    6.32 Wide Ratio

    In my thinking I see no notable advantage of the 6.32 T19 vs the T18.
    When crawling with 6.32 your going so slow that you might as well be at full stop to engage the low gear.
    And excepting dump trucks 6.32 is just too slow for a street take off ratio.

    5.11 x 3.73 differentials provides a 19/1 street take off ratio which also seems too slow in my opinion.

    And finally I get around to the Ford Borg Warner T19 @ 4.02.
    4.02 x 3.73 differentials provides the exact desirable 15/1 street low I am after.
    So in my mind the NR T19 is far superior to the non synchronized NR T18 because the low gear provides the target take off ratio that will be used quite frequently.

    The only draw back I see is that the NR T19 is not a log nor a rock crawler transmission and that’s ok by me.
    This jeep is only intended as a versatile daily driver.

    I feel that ideally with any 2 speed transfer case reduction the transfer case low range ratio should be near identical to the transmission 1st gear ratio. In that way the only redundant gear is low range x high and high range x low.

    So I already have a set of 3.15 Tera Low gears in my D20. With the proposed NR T19 it provides for a 47/1 crawl ratio which I consider as slightly marginal trail gears.
    Yet even just at 47/1 the gearing is certainly better than the long standing standard Willys crawl ratio of 37/1.
    I’m thinking a set of 4.07 Rockeaters should perhaps be the ideal transfer case reduction for the proposed combination.
    4.02 x 4.07 x 3.73 would provide an ideal trail Jeep ratio of 61/1 and everything else seems to be very well synchronized.

    Your opinions and suggestions are appreciated.
     
  4. Jan 7, 2021
    Jw60

    Jw60 Sitting up n buckled down. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Sedalia MO.
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    One question...


    Will you be ready for a Spring reunion?
    Or socially distanced spring trail ride?

    I think you will be fine round here.
     
  5. Jan 7, 2021
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    I fully agree with your summation. My recent build has 3.75:1 first with 4.10 diff gears; that puts me at 15.375:1 high range first gear, and it’s just about perfect for street use. My 1st/low is a measly 40:1, but I didn’t build it for crawling. If it ever morphs in that direction, a low-gear t-case kit or even an Atlas are always an option.

    I drove a Scout with the 4:1 T19 for years, and I absolutely loved that transmission.
     
  6. Jan 7, 2021
    Bigdaddy13

    Bigdaddy13 Member

    So.Cal
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    I’m going with a SM420.

    2nd gear is 3.6 x 4.27 = 15.3:1 2wd high take-off. Right now it’s a 2.79 x 4.27 = 11.9:1, which is alright, but i find i could use a bit more “oomph”.
    4low
    7.00 x 3.15 x 4.27 = 94.1
    3.6 x 3.15 x 4.27 = 48.4
    1.7 x 3.15 x 4.27 = 22.8

    2hi/4hi
    7.00 x 1 x 4.27 =29.8
    3.6 x 4.27 = 15.3
    1.7 x 4.27 = 7.25

    i think my numbers are right..:D
     
    Last edited: Jan 7, 2021
  7. Jan 7, 2021
    Norcal69

    Norcal69 Out of the box thinker 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    What you are doing now is exactly what I did a couple years ago.
    I am running V6, T18-6.32, D20-3.15 and 3.31 gears with 33" tires. I was shooting for 2400 RPM at a freeway speed of 70 mph.
    My trail crawl ratio is 66:1 and provides a balance between streetability, strength, reliability and off road performance.
    I rarely use 1st gear in town unless its a hill I'm taking off on or a parking lot I'm driving in. Starting in second gear with a 10:1 ratio is simply not an issue. No throttle needed or clutch feathering necessary.
    Steve is running a similar setup in his 71. V6, SM420-7.05, D18-2.46 and 3.31 gears with 33" tires. His second gear start off ratio is 12:1 and of course is effortless. His crawl ratio is 57:1, while he does have problems off road.... they aren't crawl ratio related.
     
  8. Jan 7, 2021
    oldtime

    oldtime oldtime

    St. Charles,...
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    NorCal I find you comment to be of interest.
    Yes I do have T18’s, D18’s, overdrives and lower geared differentials to play with.

    But much of this article was texted merely so I could clarify the point that few ever seem to consider useable let alone ideal street take off ratios.

    After all the take off ratio is so very important for stop n’ go driving.
    I like to reference the old 15/1 Willys standard because it seems to work so well in weaving through tight parking lots, over speed bumps and even in severe pothole conditions.

    15/1 is only an approximation and need not be exact. In my experience one needs to change something by a full 5% to 10% before the change becomes truly discernible.
    But I have occasionally heard others state that their 12/1 and even a 13/1 Jeep take off ratio was just too fast for their likes.

    So Guys, I suppose I am mainly wondering what cruise, crawl and take off ratios you all are most happy with.
     
  9. Jan 7, 2021
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Ken you are correct about 1st in a T-19 may as well be non-synchronized 6.32-1 version. As you note you must be just about stopped to shift down to first. I’ve built a coupe 4.02-1 versions for customers for the very reason you are and they were happy with the drivability of them, other than the slow shifting of a truck transmission.
     
  10. Jan 7, 2021
    oldtime

    oldtime oldtime

    St. Charles,...
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    As always Mr Miller great stuff to consider and that slow shifting fully explains why I hang onto a T15 .
    After all a man should be allowed the right to change his opinions or his Jeep parts; whichever comes first.

    Joseph; I sure hope so ....
     
    Jw60 likes this.
  11. Jan 7, 2021
    73 cj5

    73 cj5 Not ready for the junkyard yet

    Clinton, Mississippi
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    Would it be more accurate to use the effective gear ratio?

    In my case (28.8/32.5)x4.88= 4.32/1
     
  12. Jan 7, 2021
    oldtime

    oldtime oldtime

    St. Charles,...
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    I suppose in some regards an effective ratio may be more precise but I have never really played with the exact speed numbers as are seen in crawling conditions.
    You get down to about 2 mph or so and it just turns into all manner of fractions.
    Like I stated unless you change a tire diameter by 10% or so you just don’t really notice it.
    In other words 61 vs. 64 mph is not really detectable by the driver but 60 mph vs 66 is detectable.

    Most importantly I suppose that an effective number is meaningless unless you determine a standard tire as your reference.
     
    Last edited: Jan 7, 2021
  13. Jan 7, 2021
    Twin2

    Twin2 not him 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    yep passed a CHP officer in jeep once
    told him I was doing 60 . showed him the brand new speedo in dash
    he told me to adjust my speed according :D
     
  14. Jan 7, 2021
    73 cj5

    73 cj5 Not ready for the junkyard yet

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    My current ratios. Needs further testing before I can say whether or not I like them.

    F134/T98/D20

    High Range
    6.4x4.88= 31/1
    3.09x4.88=15/1
    1.69x4.88= 8/1
    1.00x4.88= 4.88

    Low Range
    6.4x2.0x4.88= 62/1
    3.09x2.0x4.88= 30/1
    1.69x2.0x4.88= 16/1
    1.00x2.0x4.88= 9/1
     
  15. Jan 7, 2021
    Mr Vaughan

    Mr Vaughan

    the d20 was marketed as silent because the intermediate shaft bearings in the d18 wore out quicker than necessary, causing an unpleasentnoise, as the rear output was offset. the centered rear output took out the wear on the intermediate shaft in 2wd, what you would be using while putting lots of highway miles on it. just an interesting fact
     
  16. Jan 7, 2021
    oldtime

    oldtime oldtime

    St. Charles,...
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    Yes the 2.46 ratio D18 (1954-1/2) was Dana Spicers initial (failed) attempt to quiet down the previous 2.43 ratio D18.
    They basically recut the tooth angle and also increased the intermediate shaft diameter.
     
  17. Jan 7, 2021
    Jw60

    Jw60 Sitting up n buckled down. 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    engine and cam also play a significant role. My 4.3 with towing cam and lighter higher compression pistons has power up to 5500rpm and is much happier running at 3600rpm on the highway than the f-134. The 2.2 was a little better at lugging down and pulling through where the 4.3 has a higher idle and will stall easier in a technical situation.
     
  18. Jan 8, 2021
    oldtime

    oldtime oldtime

    St. Charles,...
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    Yeah it’s probably impossible to arrive at any accurate engine rpm numbers for a modified engine without bolting it down to a dynamometer.

    Another good reason to run them as standard.
    Ha ha ha !

    Actually that brings up a valid question. How then does one know when engine is at peak performance ?
    Maximum vacuum tests ?
    Or estimate the rpm allowing maximum acceleration ?
     
  19. Jan 8, 2021
    Norcal69

    Norcal69 Out of the box thinker 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Even a fresh rebuilt D18 with the best of all parts and tapered bearing intermediate shaft is noisy. On top of that they create a ton of heat at any sort of highway speed. They are a good transfer case, just not designed for highway use.
     
  20. Jan 8, 2021
    Norcal69

    Norcal69 Out of the box thinker 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    It sounds to me like the perfect trans for you is the 4:1 for regular daily use. You will be in your desired take off range, and get to utilize all 4 gears.
    A crawl ratio of 47:1 is going to suit 99% of most Jeeper's driving.
     
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