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Unread 06-08-2013, 08:24 PM   #1
skizriz
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"super 18" transfer case ???

A few time now I've heard it mentioned, but can't find any information on doing it. From what I understand, this may be just what I am looking for.

I am looking to replace my Quadratrac, but want to keep my TH400.
I found a TH400 mated to a Dana 20 from a Commando.
The problem is that I want to use the off set ,and much lower output of a Dana 18. Not to mention the lower low range.
Finding a 4" bore input D18 to bolt up is turning out to be a lesson in futility.(I could imagine expensive if I do) The guy the has the TH400/D20 combo has about every other D18 made BUT the 4" bore.

He told me he's heard about putting the guts of a 18 into the 20, but said he has never actually done it. He just heard it could be done.

And information on which 18 I would need to do this ,if possible???
I could get the 400/D20 and a D18 all for $350.

I'm not finding any information on actually doing it.
From Novak..
Final Civilian, 1966-1971
The "large case" version of the Dana 18 was the most improved version of all. It was only found behind the Buick V6 engine with its T86 and T14 transmissions. The case casting used was that from the Dana 18's progenitor, the Dana Spicer Model 20. This case featured a 4" locating bore and a single stick shifter and new front output cap. The front output assembly did not provision for a shifter mounting point, as the shifter was anchored to a transmission bracket. The internals were essentially identical with the standard Dana 18. This version is best thought of as Dana 18 guts in a Dana 20 shell. Individuals can build a "Super 18" by copying this version.


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Unread 06-08-2013, 11:08 PM   #2
GraySkies
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The cases are the same. You may just need to relocate the D20 fill plug to the D18 location, since it will be covered up by the D18 output setup. Simple drill and tap for taper pipe plug, and replace the D20 fill plug with a flush one. The boss is there in the casting for the D18 plug location. It's usually just not drilled. For guts make sure you get a D18 with the same intermediate shaft size.

Google D18 rebuilds and there are some really good writeups with pictures available. This is a very doable DIY project.
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Unread 06-09-2013, 01:08 AM   #3
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Thanks. Sounds like a pretty straight up guts swap.
Any other detail I need to know. I hate to buy everything for nothing.
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Unread 06-09-2013, 06:01 AM   #4
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Think I found a glitch in your gear swap sorry I hope not.

Quote:
The Dana 20 is generally compatible with the "big hole" Dana 18. The only exception I know to that rule is the version of the Dana 20 used with the Turbo 400 in full size Jeep trucks. This version of the Dana 20 used a different splined input gear. The transmission to transfer case adapter used by the factory for the TH400/Dana 20 is known to be weak anyway.
Found here http://www.jeeptech.com/xfer/d20.html
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Unread 06-09-2013, 08:29 AM   #5
CSP
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You'd need the same Dana 18 that you can't find to make this conversion. The one with the 4" bore is also the one with the large intermediate shaft and you must have the large intermediate shaft for this swap.
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Unread 06-09-2013, 09:32 AM   #6
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any particular reason why you want to keep the offset AMC20?
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Unread 06-09-2013, 10:45 AM   #7
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the 18 is a minor version of the twenty, power went through all the gears on the 18, with the twenty it bypass the gear in 2wd, so on the 18 its a noisy transfer case because all the gears are turning all the time
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Unread 06-09-2013, 10:59 AM   #8
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There is one major reason why this will not work for you. The TH400 version of the Dana 20 has a special input gear to go to the (28 spline I think) TH400 output. There will not be a Dana 18 input gear you can use with this spline count. It would be a nice idea otherwise.
Greg
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Unread 06-09-2013, 12:29 PM   #9
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I knew it was too good to be true.

Thanks for the help guys. Back to the drawing board I guess.

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Unread 06-09-2013, 12:34 PM   #10
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Quote:
Originally Posted by TheMadMonk
any particular reason why you want to keep the offset AMC20?
Not necessarily the off set, but the output of the 18 is about 5" lower than the 20.
Having both pig on the side is nice for straddling rocks, and the lower driveline angles are always a plus.

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Unread 06-09-2013, 01:50 PM   #11
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Quote:
Originally Posted by roboto65 View Post
Think I found a glitch in your gear swap sorry I hope not.



Found here http://www.jeeptech.com/xfer/d20.html
Good find. I missed that while scouring every corner of the internet world. It's a shame the links they give are dead ends though.

Looks like I'll probably end up going with a Navak adapter for a small bore D18 when the time comes.
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Unread 06-09-2013, 02:56 PM   #12
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novak makes an adapter for this conversion so it must be doable. i would contact them directly to get the answers you need
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Unread 06-09-2013, 03:46 PM   #13
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Quote:
Originally Posted by IowaJoe View Post
novak makes an adapter for this conversion so it must be doable. i would contact them directly to get the answers you need
Yeah, I saw they had a conversion kit to do it. I was just looking to do it with parts I could scrounge up. Not only would it have been less than half the price of the Novak kit, I just enjoy building things for the Jeep myself, if possible.
Learning what parts and pieces from various Jeeps that will work together is something I have been wanting to learn about more.
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Unread 06-09-2013, 04:34 PM   #14
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Pretty much everything you need to know here-
http://www.novak-adapt.com/catalog/a...se/kit_124.htm
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