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Overdrive units

Discussion in 'Intermediate CJ-5/6/7/8' started by CJ-X, Dec 7, 2006.

  1. Dec 7, 2006
    CJ-X

    CJ-X Member

    Ohio
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    I have always wondered about the overdrive units that people install on Dana 18 cases. I have never seen one and do not know exactly how they work, except for the fact that they install on the upper rear opening. My question is could a person make it work or adapt one to a Dana 20 mounting to the lower rear output? I am sure the direct answer is no, but I don't understand the gearing process to determine if one could be made.
     
  2. Dec 7, 2006
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    It's a 2-speed planetary transmission. For it to work, you need for both axles to be driven by the intermediate gear of the transfer case. The 20 has a direct drive of the rear driveshaft (the intermediate gear is stationary in 2WD) thus it was called the 'silent' transfer case when it was introduced. The 18 was replaced by the 20 becasue 18s are, well, noisy, and the intermediate shaft wears out when it's spinning all the time. Otherwise, it's a fine transfer case, and you can easily fit the overdrive.

    The BW1339 (Quadratrac) uses a similar planetary transmission for its low range. The QT's main problem is, similar to the D18's intermediate gear, the chain runs both axles. Eventually the chain stretches and DSOs never replace it, and then the chain folds over and the case explodes. Otherwise it's a fine transfer case ;)
     
  3. Dec 7, 2006
    jayhawkclint

    jayhawkclint ΜΟΛΩΝ ΛΑΒΕ

    Oklahoma City, USA
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  4. Dec 8, 2006
    CJ-X

    CJ-X Member

    Ohio
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    Interesting. Do the saturn/warn Dana 18 units work in both high and low range? Front and rear wheels?
     
  5. Dec 8, 2006
    jeepdaddy2000

    jeepdaddy2000 Active Member

    Eagle Point oregon
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    The OD is placed between the trans and t case by replacing the bull gear. it will work in all gears and t case modes. It's use is driven by tire size, gearing, and driving preferences. I owned a 71 with 4.88's. I simply left the OD engaged for all my driving, only taking it out to wheel. Some guys like to start out in direct and use it as a fourth(OD) gear. Some guys like to split gears by double shifting(can't imagine why)the trans and OD for every gear.
     
  6. Dec 8, 2006
    jayhawkclint

    jayhawkclint ΜΟΛΩΝ ΛΑΒΕ

    Oklahoma City, USA
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    It's really nice if you've got the coin. I've become very accustomed to mine. It's not just that it lowers cruising RPM, which for me is important because I drive it on a divided highway, but I've also found it handy on the trail when you want to split a gear in low range. I'm doing a T-18 conversion, and my 1st/low/direct is going to be 76:1, so I'm thinking that the Warn is going to come in handy even more in the future; I'll be able to split gears for a 57:1 1st/low/OD, 37:1 2nd/low/direct, and 28:1 2nd/low/OD. Without the Warn, I'd be limited to a low range of 76:1 and 37:1 in 1st and 2nd, respectively. Pretty big gap.
     
  7. Dec 8, 2006
    sparky

    sparky Sandgroper Staff Member Founder

    Perth, WA
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    I recently read an article about a Dana 20 overdrive. It was designed and a few were made but they never were produced like the D18 ODs.
     
  8. Dec 8, 2006
    mb82

    mb82 I feel great!

    Charlottesville Va
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    Yeh also in that article there was a mention of a 3 speed dana 18... I want that.
     
  9. Dec 8, 2006
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    Where's you find that at Sparky? I'd like to have a look at it-

    H.
     
  10. Dec 8, 2006
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
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    As discussed a Warn/Saturn won't work for a 20, but there was another type of OD used on Willys trucks/waggies called a 'Borg-Warner" that may be adaptable. These only work in 2WD but if you want it for highway driving it may be the tickie.

    Heres a link to some info on the beastie-

    http://www.speedprint.com/Deves50/overdriveindex.php

    H.
     
  11. Dec 8, 2006
    toolbox

    toolbox If you get bored, I've got the projects.

    Hamilton, Montana
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    It's also called a "Rancho" overdrive, although they only made the adapter for bolting it to a Spicer 18. These were used on a bunch of '50s and 60's cars. I had one on the T-85 in my '63 Galaxie 500. A friend of mine had one in a '59 Rambler Super too. There was a knob under the dash you'd push in, take your foot off the gas, and it would shift into OD. Flooring it would kick it back into 3rd gear. You could either pull the knob out when you were stopped, or just floor it and pull it out when it down shifted. In Jeeps, they were mostly used in trucks and wagons...in a CJ your rear driveshaft ends up looking like two yokes with a slipjoint (someone here had a pic of what their driveshaft looked like with one). They do work though...it would certainly be an option if you could find a way to adapt it. You see them on EpaY once in a while. I really liked the one I had.
     
  12. Dec 8, 2006
    CJ-X

    CJ-X Member

    Ohio
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    I always thought that the old OD units bolted onto the back of the dana 18 where the cover plate is, and that is why I never understood how they worked, but that is why they interested me. If they just go in between the tranny and case, that is obviously much simpler, but of course lengthens everything.
     
  13. Dec 8, 2006
    Posimoto

    Posimoto Hopeless JEEP Addict

    Minden, Nevada
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    The Saturn and Warn OD fits inside the T case, not between the Tranny and T case. You pull the cover and bull gear and put in the planetary gearset for the OD. The OD housing replaces the old cover and contains the shifter linkage setup. Here's a photo showing the Saturn. The gear on the end is what basically replaces the bull gear.
     
    Last edited: Feb 24, 2007
  14. Dec 8, 2006
    LostDawg

    LostDawg Slowly rusting in the NW

    Longview, WA
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    I'm confused, so you're saying you could use a Saturn/Warn OD and maintain existing driveshaft lengths? And have OD in 2wd/4wd?:?
     
  15. Dec 8, 2006
    sparky

    sparky Sandgroper Staff Member Founder

    Perth, WA
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    Yes, there's a reason it was called the "All Range" overdrive. ;)

    Check the literature for more information.
    http://earlycj5.com/gallery2/v/picBank/od/
     
  16. Dec 8, 2006
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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  17. Dec 8, 2006
    LostDawg

    LostDawg Slowly rusting in the NW

    Longview, WA
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    Cool! Now I've got somethingthing else to investigate and maybe spend more of the wife's money... I mean my money on!R)
     
  18. Dec 8, 2006
    Posimoto

    Posimoto Hopeless JEEP Addict

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