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Some Guidance Please

Discussion in 'Early CJ5 and CJ6 Tech' started by Cowboyjeeper, Jun 19, 2020.

  1. Jun 19, 2020
    Cowboyjeeper

    Cowboyjeeper Member

    Show low az
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    Hey
    While im driving it with the f head im working on putting together my v6/v8 upgrade drivetrain im considering gearing and such its on 33s

    i have a sbc and know where i can get a low mile 225 duantless cheap.

    1. go 3.73 but sm420 and terra low for trails? on paper seems to be best of both worlds but pricey.

    2. 4.88 to 4.27 sm 420 with standard transfercase gears and over drive.

    thoughts and criticism welcome
    Thanks
     
  2. Jun 19, 2020
    jpflat2a

    jpflat2a what's that noise?

    Hermosa, SD
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    What is your drive train configuration now ?
    I would vote for #2 above.
     
  3. Jun 19, 2020
    Norcal69

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

    Northern California
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    Option number 1 and never look back! Your crawl ratio will be 82:1 and you will be able to cruise the freeway in the 2600 rpm range. 82:1 is plenty of crawl ratio to do rubicon type trips. Best of all worlds and way stronger without an overdrive.
    I am running 3.31 gears with 33's, t-18 and terra lows through a D20 with 66:1 crawl ratio.
    Steve is running 3.31 gears with 33's, Sm420 and standard D18 and he loves it as well.
    Literally no one understands why it works so well until they ride in or drive my jeep. If I didn't freeway drive often I would have gone with 3.73 in mine.
     
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  4. Jun 19, 2020
    chipdom

    chipdom Member

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    My vote would be number one with the Dauntless
     
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  5. Jun 19, 2020
    colojeepguy

    colojeepguy Colorado Springs

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    488 gears and an overdrive is an ideal combination for a Jeep IMO not only do you get the best of both worlds but you have the ability to split gears which is a great benefit off road. Don't forget that the truck type 4 speeds are in all reality a 3 speed + granny gear....being able to split those gears is really nice.
     
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  6. Jun 19, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Another option is 3.73, no overdrive, and truck 4-speed. Low range is 2.42 already with a Dana 18, and that's better than a 50:1 crawl ratio. What axles do you have now? I would not try too hard to optimize on paper, without using and driving the Jeep a whole bunch. 50:1 is really low.

    IMO an SM420 is quite antiquated ... a T-18 or NP435 or SM465 is roughly the same, and perhaps more available. Just depends on what you can find locally.

    Another combo might be V6, T-15 (or T-14, or T-86), Terra Gears, 5.38s and an overdrive. Also near 50:1, and the 3-speed is like a car transmission compared to the truck 4-speeds. I only have experience with the T-18, and I believe that's an easier shifter than the SM420.

    Or how about V6, TH350, Dana 18 and 4.27s? No need for as deep gears with an automatic.
     
    Last edited: Jun 19, 2020
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  7. Jun 19, 2020
    Sierra Bum

    Sierra Bum Member

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    I feel like with these old rigs there’s lots of good ways to do it. And there’s certainly some proven formulas. A lot of it is personal preference and driving style.

    I run option 2 with a V6, warn OD, an sm420, 4.88s and 33s at 84:1. Im also running ARBs front & rear. I’ve never had a problem with an overdrive. And I love being able to split all my gears. I like shifting and like the options. I use my OD all the time. So of course this is my preference. The only change I want to make is terra low gears for 100:1 ish...just because. But I’m in no hurry...it’s actually already close to perfect..for me.
     
  8. Jun 19, 2020
    Sierra Bum

    Sierra Bum Member

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    Another thought. The V6s are perfect for the short-nosed cj5. They fit perfectly and are powered well for the weight and size. Although guys like them, the v8s are a tight fit for my tastes and harder on everything. Personally, I’d probably look at a SBC in an intermediate though, among many other upgrades.
     
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  9. Jun 19, 2020
    Jeepsterjim

    Jeepsterjim Member

    Lincoln, CA
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    401
    225 V-6
    SM-420
    Large mouth 18 with low gears
    over drive
    4:27 gears
     
  10. Jun 19, 2020
    Keys5a

    Keys5a Sponsor

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    What SBC do you have? I'm a fan of old 283's, or maybe as large as a 327. Anything larger produces a lot more torque. The 420 and D18 can take it, but not so much for the axles, especially with 33s. I'd be looking hard at using the 225 unless you have a small displacement SBC.
    -Donny
     
  11. Jun 19, 2020
    Muzikp

    Muzikp Active Member

    Sacramento Ca.
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    I'm using the Dauntless, SM420, D18, 33's and 4:10 gears. It's pretty darn good to me, a good crawl ratio and not screaming on the freeway. I feel like the V6 is the right size, weight and torque for the little CJ.
     
  12. Jun 19, 2020
    Cowboyjeeper

    Cowboyjeeper Member

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    Currently f134 t90 d18 and od. 5.38 gears
    I have a 5? 263? Sbc (real early no full flow oilfilter) its hooked to t90 d-18 with od. I also have the sm420 is why i suggested it.

    Obviously going to do steering and brakes as well.

    i will daily drive this so it would be nice to atleast not be a hazard if i have to use the freeway

    So much info, thanks everyone. Im not g
    Ignoring anyone jut too much to put in one reply.
     
  13. Jun 19, 2020
    Cowboyjeeper

    Cowboyjeeper Member

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    True, i have overdrive.
     
  14. Jun 19, 2020
    Cowboyjeeper

    Cowboyjeeper Member

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    you always have such good input. I already have an sm420. I think ill use that. I am currently driving it as a f134
     
  15. Jun 20, 2020
    Norcal69

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

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    When all your reduction takes place at the axles you bind the drive train, increase rolling resistance and heat...... :whistle:
     
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  16. Jun 20, 2020
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    This is very true, but at the same time you reduce the torque everything upstream of the axles sees. Drive shafts, transfer case, ...etc. For mostly on-road use, you're probably better to less reduction at the axle for efficiency and more reduction to reduce drivetrain strain for mostly offroad use.

    My plan is to do 225 V6, T-98, overdrive and 4.88s in the '71. That will easily cover any offroad/onroad driving I want to do with lots of splits in the middle. All the parts are sitting in the shop, I just need to find the time.

    I also want 4 shifters like my Dad's flatfender and my CJ-2. I grew up that way and to me all jeeps should have at least 4 shifters and yet another for the PTO. It's part of what makes old Jeeps special to me. I love shifting and you can shift up and down all day long. I would always drive my CJ-2 like a 6 spd using the overdrive to split gears on the way up and down.
     
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  17. Jun 20, 2020
    AKCJ

    AKCJ Active Member

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    I’ve got the same setup as Muzikp. Like he said it works great. It’d be fun to add terra low or OD but it’s not needed.
     
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  18. Jun 20, 2020
    Fireball

    Fireball Well-Known Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Also, this calculator is a great resource: Speed Calculator

    You can put in your tire size, pick existing transmissions and transfer cases or enter your own ratios. It will show you the crawl ratio and also the road speed at a given RPM. I used it to decide on 4.88s given the rest of my combo.
     
  19. Jun 20, 2020
    Norcal69

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

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    This is exactly my point. Reducing strain on the entire drive train rather than binding it all up at the axle. A lil reduction at the trans, a lil reduction at the t case, really spreads out the load on the drivetrain.
     
  20. Jun 20, 2020
    Cowboyjeeper

    Cowboyjeeper Member

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    guess im having a slow moment im not understanding what you mean?
     
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