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All Kinds Of Questions

Discussion in 'Flat Fender Tech' started by rml1708, Aug 8, 2019.

  1. Aug 8, 2019
    rml1708

    rml1708 New Member

    washington
    Joined:
    Jul 28, 2019
    Messages:
    10
    I done did it. I bought a 51 M38 with a Buick 225 V6. Currently it has a T90 and a T18 in it. I am looking into a SM465 with the T18. Novak adapter appears to be the best bet even though I will pay more for the adapter then the engine and tranny combined.

    What can I expect from the Stock Dauntless, the Stock SM465 thru the T18. I am planning on running a 30 or 31 inch LT tire (BFGoodrich All Terrain K2 or equivalent). I want a comfortable 60 mph driver that will do fairly well off road. I am not a crawler I am a weekend get out kind driver. 90% daily driver 10% off road.

    How much sheet metal work is required to do this kind of tranny swap? Is there a nice descriptive forum that has a guy doing this type of swap that I can see what was done?

    Should I just stick to the T90 and get an overdrive? Is the SM465 still going to need an over drive?

    I have a Weland 4 barrel intake I can use and will consider the original 2 barrel or the 4 barrel or maybe even Fuel injected down the road.

    Any warnings cautions watchout for's in doing this?

    Any inputs comments welcome.

    Thanks,

    Robert
     
  2. Aug 8, 2019
    73 cj5

    73 cj5 Not ready for the junkyard yet

    Clinton, Mississippi
    Joined:
    Jan 10, 2014
    Messages:
    2,137
    T90 and sm465 or 420 or any other truck 4 speed is direct drive in 4th gear- 1:1. If you want to go 60 without wearing the engine out you’ll need a different gear ratio or overdrive. Increasing tire diameter is my go to for slightly changing engine rpm at cruising speed but it’s not ideal.
    This is assuming you have 5.38’s.

    :pics:
     
  3. Aug 8, 2019
    Howard Eisenhauer

    Howard Eisenhauer Administrator Staff Member

    Tantallon, Nova...
    Joined:
    Nov 22, 2003
    Messages:
    8,102
    First question is why do you Feel The Need for Slow? The only thing a truck tranny buys you over the T90 is a good crawl ratio, if you're worried about the 90 taking the v6 torque it will be fine.
     
  4. Aug 8, 2019
    Boyink

    Boyink Super Moderator Staff Member

    Tulsa, OK
    Joined:
    Sep 20, 2002
    Messages:
    6,193
    10% offroad? Stick with the T-90 and look for a warn OD.
     
    OldAdobe and FinoCJ like this.
  5. Aug 8, 2019
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
    Joined:
    Jul 18, 2013
    Messages:
    5,593
    agreed...making it a comfortable 60mph will be more about steering, alignment, brakes and suspension more than anything else. But the OD will really help get you to 60mph if you do have 5.38 gears. If you have 31" tires with 5.38 gears, and either the T90 or SM465 (both 1:1 highest gear), 60mph will require 3500 rpm. If you run a typical 0.8 OD with the same set-up, 60mph will be 2800 rpm. You gain nothing for the highway cruising with an SM465 vs the T90, but the OD is very helpful (and allows for gear splitting: example would be 2nd+OD is between 2nd and 3rd gear). Unless you are REALLY 4wd rock crawling, the truck granny gear 4-speed isn't all that helpful...I just ran the rubicon with a 3speed and about the same crawl ratio as you would have. A truck 4-speed would be nice, but I would never trade my OD for a 4-speed.
     
  6. Aug 8, 2019
    rml1708

    rml1708 New Member

    washington
    Joined:
    Jul 28, 2019
    Messages:
    10
    if i understand the SM465 buys me nothing for road speed as final gears are all the same for T90, SM465 or SM420. the SM465 gets me a lower first gear that is the advantage. Looks like I need to go find an overdrive for the T18 and have Herm rebuild it

    thanks for that info
     
  7. Aug 8, 2019
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
    Joined:
    Jul 18, 2013
    Messages:
    5,593
    Yes...and just to avoid a bit of terminology confusion...the transfer case is a D18 not a T18. T18 is a truck 4 speed transmission. Herm can help you with the OD, or you can contact advanced adapters ad they carry new ones.
     
  8. Aug 11, 2019
    sterlclan

    sterlclan Member 2022 Sponsor

    exploring the...
    Joined:
    Feb 21, 2009
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    3,869
    unless you like the skinny pedal on the right too much.
     
    Rich M. likes this.
  9. Aug 11, 2019
    47v6

    47v6 junk wrecker! 2023 Sponsor 2022 Sponsor

    USA
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    Oct 25, 2006
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    Why don't you just drive it and see what, if anything, you need to do to make it more fun.
     
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  10. Aug 11, 2019
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Yep, make it stop, steer and go in that order. An M38 should have 5.38s. These Jeeps are very competent without any modification, and will go some amazing places.

    The Warn/Saturn overdrive is a terrific accessory for these Jeeps with the Dana 18 (D18) transfer case. For the knowledgeable buyer, an overdrive should add about as much value to the Jeep as the purchase cost, and it would make driving this Jeep more relaxed and enjoyable.

    These Jeeps have a lot of moving parts, nearly twice as many as their automobile contemporaries, and this is mid-20th-century technology. People sell cars for a reason, and I would expect any new-old Jeep to need quite a bit of (deferred) maintenance to bring it up to roadworthy and reliable. I would expect knuckles, bell crank, steering gear, D18 intermediate shaft, T-90 2nd gear, springs, shocks and bushings, assuming normal wear, will all need attention. Most find the factory 9" brakes unsatisfactory, especially above boulevard (convoy) speed.

    Should be reprints of the mil M38 manuals out there; these manuals are typically very thorough, since they may not have experienced personnel available for maintenance in the field. You could also use the Late CJ-5 manual to cover the V6 engine.
     
    Last edited: Aug 11, 2019
  11. Aug 11, 2019
    duffer

    duffer Rodent Power

    Bozeman, MT
    Joined:
    Sep 17, 2009
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    4,459
    Yep!!! With the 225, you can do a lot of reasonably difficult off-road without a real low gear transmission, especially if there are still 5.38 gears in the axles. IMO, an overdrive is absolutely a must with this combo. If you do decide to get an OD, try to find the Warn version.
     
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