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Gear selection

Discussion in 'Early CJ5 and CJ6 Tech' started by Farmer Mike, Nov 23, 2011.

  1. Nov 23, 2011
    Farmer Mike

    Farmer Mike Member

    Butte City, Ca
    Joined:
    Sep 21, 2011
    Messages:
    121
    I have 2 routes I can go.

    1. SM420, D18, 4.27 gears, 35" tire.. This would result in a 74:1 low range

    2. SM420, D18, 5.38 gears, OD, 35" tire.. This would result in a 93:1 low range

    I'm guessing there is about a 4-6 mph difference between 1 in high range and using the overdrive on 2.

    Reason I'm asking is the Dana 30 I just bought has 4.27 gears and the offset Dana 44 I just bought has 5.38's and also 1 piece axles. So one way or the other I have to buy one set of gears.
     
    Farmer Mike, Nov 23, 2011
    #1
  2. Nov 23, 2011
    Patrick

    Patrick Super Moderator Staff Member

    Los Alamos, NM
    Joined:
    Sep 22, 2002
    Messages:
    8,360
    I'd go at least 4.88...5.38's would be better with 35's.
     
    Patrick, Nov 23, 2011
    #2
  3. Nov 23, 2011
    bkd

    bkd Moderator Supreme Staff Member 2022 Sponsor

    K-Town Tenn.
    Joined:
    Apr 29, 2007
    Messages:
    3,294
    Dedicated crawler? Street DD duties? How you plan using it dictates what gears imho
     
    bkd, Nov 23, 2011
    #3
  4. Nov 23, 2011
    duffer

    duffer Rodent Power

    Bozeman, MT
    Joined:
    Sep 17, 2009
    Messages:
    4,519
    Missing from the discussion is the engine. With a 7:1 first gear, IMO, the 5.38's are a waste of time (and gas) with everything except maybe the 134. Assuming you are at a minimum with a 225, the OD would be going in there in either case if it was mine.
     
    duffer, Nov 23, 2011
    #4
  5. Nov 23, 2011
    Corveeper

    Corveeper Member

    Chanute, Kansas
    Joined:
    Jul 29, 2005
    Messages:
    817
    Got a friend that built an old Bronco with a flat nasty 351W and 37" SS Boggers. When he ordered gears he said he was debating between 4.56's and 4.88's but when the call went through at the last minute he blurted out 5.13's and has regretted it ever since. It's just too short of a gear for anything but off roading.
    Myself, I've got a similar setup to what you're thinking about, SM420, Dana 18, 4.27's but 33" tires, and it'll spin about 3200 RPM holding 65-70 MPH down the highway. An overdrive would make it just about right.
     
    Last edited: Nov 23, 2011
    Corveeper, Nov 23, 2011
    #5
  6. Nov 23, 2011
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
    Joined:
    Sep 23, 2002
    Messages:
    12,529
    All depends on usage. I like the 5.38's in the 59/5. Works extremely well off road but not so good on road wit 33's. With 35's it would be better. An overdrive would make it fine for street driving. If mostly street driving then a little taller gear would be better. I think 4.27, 35" tires, and an overdrive would be too tall. You have to take aerodynamics and rolling resistance into account when you start going that big of a tire
     
    nickmil, Nov 23, 2011
    #6
  7. Nov 24, 2011
    Farmer Mike

    Farmer Mike Member

    Butte City, Ca
    Joined:
    Sep 21, 2011
    Messages:
    121
    The engine is an injected turbo V6. There wouldn't be a overdrive on version 1 with the 4:27 gears. Only with the 5.38. Not gonna be a rock crawler but it will see mountains, mud, and trails along with driving it to town. 65 mph I can more than live with in a jeep.
     
    Farmer Mike, Nov 24, 2011
    #7
  8. Nov 24, 2011
    jeepcj

    jeepcj Member

    cincy, Ohio
    Joined:
    Aug 23, 2009
    Messages:
    601
    I have 4.88 on 35's, wide 35's(14.50) with a muncie 4spd and the warn OD. I love the OD and if had a choice, theres no way I wouldn't use it if I could. Id go 5.38 with the OD, if you go 4.27's Id use the OD as well. It would be useless to you at lower rpms, but may save some gas on the highway. JMO
     
    jeepcj, Nov 24, 2011
    #8
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