Dana 18 for QT swap

[Frustrated]

It figures that the same month I convert my QT to cable shift that I find a super cheap Dana 18 20 miles away!

Anyway, I have have been searching the archives for infor on this swap and am a bit confused. Will a Dana 18 swap directly onto a TH400 that previously had QT? I know you need an adapter (Dana 20 or after market) and new input shaft but what about the driveshaft clearance? Also, I read in the archives about swapping the guts of a Dana 18 into a Dana 20. Wouldn't this defeat the purpose of the passenger side output of the Dana 18? Very confused and would like some help.

P.S. You don't even have to answer my questions if you have a part time QT without OD that you would like to trade/sell. I have a full time QT and a part time with OD QT. The only thing that needs to be swapped is the chain and the passenger side sprocket.

[Frustrated]

Ok I did some more searching and found out that you can use the Dana 20 housing to hold the Dana 18 internals and still have a pass. side output, right? Good news, except now I have to buy two t-cases!!

[River Beast]

Porkchop and/or Scotty would best answer you questions..

The TH400 tailshaft needs to be swapped out and the Dana 18 adapter plate will nbe needed...

One reason people swap the guts around is for the gearing... the 18 has a 2:46:1 low as the 20 has a 2:1:1.

The D18 also runs thru the gears to the rear output due to the offset output.. where the D20 has direct drive thru the TH400 tailshaft and stubshaft in the 20 to the rear output.

One thing to look for on the 18 is the soze of the intermediate shaft... there are 3 sizes 3/4" up to 1 1/4".. the larger being the preferred.

Another is the bore on the case (talk to Scotty on this one)... I believe there are 2 size bores... 3.5" and 4" Don't quote me on this... but I am close.

One last thing... if the 18 came off a standard tranny... and new input gear will be needed... Talk to Porkchop on this one...

I gave up what I know and pointed you in the right direction... good luck... there is more info to be had by the 2 members I mentioned and many more... ;)

[porkchop]

RB pretty much said all there is to say. The to different housing for the the D18 are the 3" and the 4". If you swap all the guts of the 18 into a 20 case then it does not matter.

Also you are not able to attain the 2.46 low range with the auto tranny due to the fact that the only main gear count for the auto is 26 tooth and you will need a 29 tooth main input gear. You can have one made, but I am sure that will cost you. If you choose to run with the 26 tooth gear (I did) then you will have to make sure that it is the right degree cut gear. There are two different gears the 18-8-40 and the 18-8-43 the first being 20 and the latter being 17.5*.

This may all seem very confussing but when you get down to it it is very easy. If you keep searching you will see some good post about this subject. Some are long and detailed.

[blackjeep2002]

When I did this on mine, the swap itself was pretty easy. Make sure you have all of the parts ahead of time. You will need to get an adapter for the tcase to bolt up to the tranny after you remove the QT. The QT adapter will not work. Advance Adapters or Novak have them. Also, your rear driveshaft will need to be lengthened and your front shortened. About 2" for both is what worked for me. A CJ front will work (if it is the right length) because then you will not have the cv joint on it anymore. You will not need the cv anyway, and the bolt holes to bolt it up to the differential will not line up (at least they did not on mine).
Go with the tips from the other 2 gentlemen and good luck swapping.
Keith :cool:

[scotty]

again,not much more to add smile.gif the large hole 18 that will directly replace a d20 is fairly rare,only coming in vehicles equipped with the "dauntless" buik v6.

if you buy an AA or novak kit,you will not need to screw with swappig guts as the kit can be bought for the small hole xfer cases. be forewarned,tho, that the 18 housings are somewhat weaker then the later 20 housings. swapping the guts can be a way of "making your own" large hole 18. if you do it this way,the housing is alittle beefier and you will not have to pull the input gear to pull the xfer. it can stay attached to the tranny and will slide thru the 4" hole.

the important thing to remember is that the input gear must match the rest of the t case gears. as PC said,there are several different tooth counts and a couple different pitches of the gear tooth cut.

this brigs us to the prollem of using the factory th400/d20 adapter and tailshaft. the factory stuff has an odball spline count on the tailshaft(15),and there are only a couple of input gears avaialbe that will work with certain years of the d18.all other jeep applications of d18/20 are either 10 or 6,with 6 being the most common. again,like PC mentioned,you will not be aboe to create a 2.46 d18 that will swap onto a factory tailshaft,do to the non-existance of an input gear with 29 external teeth AND the correct interal splines to fit the factory shaft.

in other words,i believe you are better off buying a novak conversion kit,unless you have or happen to find,a factroy setup very,very cheap. even then,you are somewhat limited to xfer swaps do to the fnky pitch used in some of the factory th400/d20 xfer cases. the conversion kit will iclude a 6 spline tailshaft,giving a much broader selection of repalcemet d20s and d18s.

the hardest part is swappig the tailshaft on the tranny smile.gif

at any rate,i personally like gear driven xfer cases(specially when we are comparing them to a case that drives BOTH :eek: outputs) for a rig that will be used hard.i think the $$ is better spent on a conversion kit rather than a part time kit if you use it hard(wheeli,towing,etc.)

further questions? smile.gif

[ May 22, 2002: Message edited by: scotty ]</p>

[Frustrated]

Thanks for all the replies! Unfortunately, there seems to be too much money involved in this swap for me. I agree with you Scotty, I would much rather have a gear driven case. But, since I already have a QT that is converted to part time (with the F#&*ing OD) and it is manual shift, I will have to be content for awhile. Thanks again. If anyone wants a Dana 18, let me know. I know of several near me (Erie, PA) for around $100.