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Dana 20 Swap Reality Check

Discussion in 'Early CJ5 and CJ6 Tech' started by kenb, Mar 22, 2023.

  1. Apr 4, 2023
    Norcal69

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

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    This really depends on how your jeep is set up.
    Throw a soft top or hard top on a jeep with a D18 and run it down the freeway at 60-70 mph for an hour and you'll be very intimate with the D18 noise and heat.
    Having run both a standard shaft and tapered bearing shaft, the tapered bearing setup does help with noise and heat, but its still definitely there.
    If you cant hear the D18 over your exhaust...... then you better put some ear plugs in because your doing serious damage to your hearing...... probably too late in the hearing department for some of you...... (y) Not to be the safety police ...... just stating fact. We will leave Harley riders with brain bucket helmets and no ear plugs out...... They are crazy enough already.

    The OP is looking to outfit his jeep for highway/distance travel, thus his consideration of getting a YJ over in another thread.
    Outfit an early CJ5 with a good condition V6, 3 or 4 speed trans, D20, 3.73 gears and 33" tires. It will cruise the freeway just fine, have plenty of power, operate cooler, be more comfortable and more reliable. The D20 is a far more efficient transfer case for highway speed applications.

    The ability to put an overdrive on a V6 with 3.73 gears..... Why?
    At 65 mph with 31" or 33" tires your barley scratching 2000 rpm, pretty much lugging with engine while trying to overcome wind resistance.
    There is no advantage to to an overdrive on a V6 jeep with 3.73 gears and if you think your going to split gears between the trans and overdrive while accelerating onto the freeway and merging with traffic......
    Well, you can justify that overdrive purchase however you need too..... but the same jeep equipped with V6, D20 and 3.73 gears blew your doors off and merged with traffic already.
    You can build a D20 into 2.46 low version just like a D18, or go with terra low gears and get more crawl ratio.
    It is far more efficient to build crawl ratio in the transmission and transfer case than it is to bind up the drive train at both ends low axle ratios.

    I have done the D18 to D20 swap as well as the rear swap from offset to centered rear. Here is what you need to consider:
    The centered diff will have larger diameter axle tubes, you will need new ubolts and lower spring plates.
    When you swap your brakes over, there will be 2 new holes that you need to transfer to the backing plate from the axle housing flange.
    Your rear drive shaft length will change, depending on your setup, it may or may not need to be shortened.
    If you have a decent sized lift you will need a double cardan drive shaft to address the increased angle and vibration.
    If you twin stick the D20 like a traditional D18, minimal floorboard modification is required. You can use a traditional transfer case 2 stick boot and ring.
    If you stay with the standard single stick shift arrangement you can still use the standard stick boot and ring from a 72-75 CJ as the early and intermediate have the same basic floorboard shape.
    Something no one else mentioned...... The intermediate CJ rear axle will not line up perfectly with a D20 output when installed into an early V6 jeep frame. The early V6 engine offset still places the D20 output a couple inches off to the left of the chassis center line. It is not an issue but does make it more important to get your drive shaft angles correct. Getting your drive shaft angles "good enough" will still probably leave you with a little vibration at high speed.
    A postal CJ rear axle is actually the perfect offset to the left to mate up with a D20 in a V6 chassis. It however is not a straight bolt in as you will have to weld on new spring perches to fit the early frame.

    Just my experience from doing this conversion.
     
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  2. Apr 4, 2023
    duffer

    duffer Rodent Power

    Bozeman, MT
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    Those shafts are most definitely NOT install and forget. IME, you need to pull the pan and adjust the preload about every 10k or they do go to pieces. They also can go to pieces if you set the preload too light during the install. Overall, I still think they are worth it.

    As to the OP, lateral offset on driveshafts isn't too big a deal if it is small. Maybe my eyes are bad, but it appears to me that Willys/Kaiser even cheated on the offset axles and the D18's. Those appear to have the pinion offset slightly towards center, no doubt to keep the right side spring perch off the cast housing.
     
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  3. Apr 4, 2023
    oldtime

    oldtime oldtime

    St. Charles,...
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    Here’s my take.
    After AMC got hold of Jeep they started turning them from offroaders into street machines.
    And so most of the AMC changes reflect that.
    Particularly the transfer case which lies at the very heart of the Jeep.
    It is far easier and cheaper to take a post 1971 cj and turn it into an off-reader than to take a pre 1972 and turn it a street machine. Either can be done yet must be done right.
    When converting either way the biggest issues by far
    is the left/right placement of the power train.
    The power train being the engine, clutch transmission and transfer case.

    Here is an example of the first left/right change that occurred in 1966 when the Dauntless was introduced.

    All 4 cylinder CJ’s prior to 1966 had the engine placed 2” left of frame centerline. With the Dauntless the engine and remainder of drivetrain was moved to the right exactly 1-1/4 or 3/4” left of frame centerline.
    With a Dauntless this must be done to fit a D20 into it’s proper location.
    Any remaining rear prop shaft r/l alignment is negligible in its effect so long as it’s the center flanged D44.
    And yes a double cardan constant velocity yoke must be used attached to the rear propellor shaft when the shaft angle is steep due to inherent short wheelbase.
    An 81” wheelbased cj-5 with D20 will require the constant velocity yoke.
     
    Last edited: Apr 4, 2023
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  4. Apr 4, 2023
    colojeepguy

    colojeepguy Colorado Springs

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    It's REALLY difficult to adjust it with the transr case installed in the Jeep.

    Aren't intermediate CJ's the same distance between tcase and rear axle?
    I know the wheel base was stretched but I thought that was all up front....
     
  5. Apr 4, 2023
    Norcal69

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

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    Your correct.
    The D20 output is higher than the D18 output.
    What oldtime is referring to is if the jeep is lifted, it will need a double cardan joint at the transfer case.
    Stock height suspension a standard U joint is just fine.
     
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  6. Apr 4, 2023
    oldtime

    oldtime oldtime

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    Well in my build I started with CJ3A 80” wheelbase.
    Moved the Dauntless toward right side as compared to an L134. T18 and tera low D20 behind that with transfer case remaining in standard fore/aft positioning.
    My rear prop angle was too steep so I had to shorten the propellor shaft and add the constant velocity joint. All with non lifted standard suspension parts.
    Also my D20 is set up with the parking brake which pushes the rear yoke a tad further toward the rear.

    Jeep tera low 3.15 with Jeep rear park drum and factory IH twin sticks.
    Custom mounting bracket to correctly position the early type snubber.
    [​IMG]
     
    Last edited: Apr 4, 2023
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  7. Apr 4, 2023
    vtxtasy

    vtxtasy oldbee 2024 Sponsor 2023 Sponsor

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    I know you probably posted it somewhere but I would like to see the parking brake on the D20. From what i have experienced, a double cardan is a good upgrade to any D20.
     
  8. Apr 4, 2023
    oldtime

    oldtime oldtime

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  9. Apr 4, 2023
    vtxtasy

    vtxtasy oldbee 2024 Sponsor 2023 Sponsor

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    Thanks. That is a neat setup. I won't ask how. The driveshaft is probably just a little shorter the the D18. Roughly 16-17".

    Pretty slick as only you could do.
     
    Last edited: Apr 5, 2023
  10. Apr 4, 2023
    oldtime

    oldtime oldtime

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    Sorry bout the poor lighting I shoulda put a lamp on when taking photo; maybe tomorrow I will.
    I suspect the drive angle would be too steep even if I pulled off the park brake assembly and connected to a standard transfer case output yoke.
    (I may have to do that yet if I sense vibrations.)
    So I went ahead and put the double cardan on it and shortened the tube.
    I’ll check OAL later but it’s actually a tad longer than a standard 3A propellor shaft.
     
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  11. Apr 4, 2023
    3b a runnin

    3b a runnin Active Member 2023 Sponsor 2022 Sponsor

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    I like that
    I am definitely interested in the d20 with the drum park brake. I've had pretty good luck with the drum park brake on my d18's. I'm considering a 700r4 /d20 combo in the cj6. Not in the immediate future but it doesnt hurt to start planning.
    I figured the auto with 4.56 or 4.27 gearing would be a decent compromise.
     
  12. Apr 4, 2023
    colojeepguy

    colojeepguy Colorado Springs

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    I think the D20 with parking brake was a 60's J truck thing.
     
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  13. Apr 4, 2023
    oldtime

    oldtime oldtime

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    Right the park brake D20’s came with some early j trucks. The iH factory twin sticks are awesome.
    Note how the pinion was tilted up to fit with the double cardan constant velocity joint.
    [​IMG]I would have preferred a two joint propellor shaft but the angle was just too steep. A two joint propellor shaft would be sufficient on a cj-6, and would not require tilting the differential pinion upward.
     
    Last edited: Apr 4, 2023
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  14. Apr 5, 2023
    vtxtasy

    vtxtasy oldbee 2024 Sponsor 2023 Sponsor

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    That angle looks good. It all looks good! Is this where you are at currently?
     
  15. Apr 5, 2023
    oldtime

    oldtime oldtime

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    Yeah that project has been set aside for the past year due to health issues. Hope to get back at it this summer.
    1951 CJ3A with 1970 factory frame mounted dauntless. Oem Borg Beck diaphram clutch. Jeep wide ratio T18 with case modified to GM pattern.
    Tera low 3.15 D20 with IH factory twin sticks and Early J truck parking brake assembly. Custom propellor shafts. Center flanged D44 rear with 30 spline Powr Lok. D30 with Powr Lok @ 3.73 ratio.
    235/85R16 6 ply Pirelli’s mounted on rare 6”x16” early 60’s Jeep truck wheels. Standard 3B suspension and frame.
    CJ Saginaw Power steering box.
    Custom stainless dual exhaust into single muffler and two tailpipes. Jewels stainless 3A body from the late 1970’s. OEM NOS Kelly half cab. Electric intermediate CJ wiper motors. Dual stainless fuel tanks and much more to come.
    Nearly finished with exhaust at this time and ready to do some body fitment and required changes.
     
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