Just to clarify.....I have gutted 208s on several occasions to achieve other results. I feel confident it would be reasonable to gut one to create an underdrive.

All you want from the 208 is the input and output shafts...the tail shaft and yoke....and the planetary. The case would need to be sectioned, inverted and a top plate made. All of this could be done with hand tools at home....no radial indexing is necessary.

Note: My mods to 208s have been to make a "locked" low range chain drive. Much of the monkey motion in the 208 is for 2wd and high range operation. These parts are easily removed for alternative uses. About half the number of parts disappear in the 4wL mod.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Oh. I did misunderstand. So basically you drive around with the 4WD unit in "hi" and then switch to "low" at the track. That's backwards form what I want to do.

2.76x2.70=7.45 (holy crap again)

I still haven't gotten an email reply from maximum overdrive, I suppose the length of the 904 t-case plus adapter plate will play into whether I would need a custom O.D. shaft... and I don't know that length...
Assuming my contraption was no longer than the one they sell to bolt on the th400 all I would need from them is the shaft connecting cylinder, but with 26 splines on the trans side.

Sandy, do you think the planetary gears from later new venture cases could be put in the 208 without major surgery? The 2.7:1 reduction is the weak point to me, personally since I would be limited in rear ratio.

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!

The TH400 is a very short output shaft tans v/s a 904.

I use a 2wd TH400 coupled with a homemade adapter to a 4L modded 208. I do this because 2wd TH300 cases and ouput shafts are free like slants and 4x4 cases and shafts are expensive like Ferraris. The 2wd shaft is 6" longer than the 2wd.

On a 2wd 904 you have a very long outout shaft,,,,,hence the crazy, long,cast adapter ..... or separate driveshaft

The output shaft is long enough that Chryco replaced it with an internal OD and called it an A 500........

You could build an OD with a planetary and input and output shafts.....Laycock did this and called it an M46....

Find (if it exists) a slant 904 with the 4x4 output shaft and transfer case adapter....and adapt the M46 to it in place of the transfer case.

(this is my kind of hot rodding)

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Yeah....Im the one who destroyed this rare, vintage automobile.....

This is exactly what I'm going for. I believe the difference between 2wd and 4wd 904s is that on a 4wd the rear tailshaft housing is replaced with the "4wd adapter" I referenced finding on ebay earlier.

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!

What I should have said here is 904 transfer case adapter plus my OD to adapter adapter plate (all this adaptation has me feeling darwinian...)

I think that this option is now emerging as what would clearly be best versus the transfer case underdrive idea.

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!

Its not very difficult to mimic a 4x4 tranfercase adapter. ....specially if one end needs to be modded for the M46. I made mine from 1/4" flat iron.

All you need is a plate that mimics the tailshaft housing face on the 904.....and a plate that mimics the tailshaft face on the Volvo trans (the one the M46 bolts to) connected by a piece of steel tube.

The shaft coupler is pretty straight forward.

A driveshaft is very easy.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Deleted: Answered my own question.

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!

Got a reply from Maximum Overdrive...

"yes i can help with the shaft.you must get the two pieces welded togther strait or you tear somthing up."

"or you tear somthing up"

This crap kills me...

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!

I like the term " wadded up "

The dude was referring to "Indexing" a key concept for any 'dapting.....

There are 50 ways for a poor man to ensure his project is indexed to the shaft centre line.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Humor me, since I'm green as a spring twig; and review some of these ways for me.
I have ideas, but you've been there and done this stuff....

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!

I used to work as a fitter at a machine/ welding shop.....but that was 30 years ago.

I dont own a dial indicator.

I do have a digital caliper and feeler guages.

When building an adapter for between cases you need to ensure the ends plates are parallel. ....all through the assembly process. You dry fit the end plates and tube. I like to bolt them together through the shaft plane. the shaft plane is where the shaft would run through the middle. You use your cheap digital calipers to ensure the end plates are square before you weld. Then you zzzt 1 place.....roll it over and zzzt again. Check for square....zzzt again....roll over zzzzt again.....check for square.

Next time we will chat about the shaft coupler.....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Hit me man! I'm all ears!

My Idea for the shaft coupler is to take the output shaft from the volvo trans (Should slip over the o.d. input shaft) and a 904 slip yoke, cut a section off of both and weld together. Yes I would make sure they were centered with respect to one another and parallel before welding up.

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!

904 TorqueFlites with a short transfer case 'tailhousing' and matching short output shaft were used in early 1980s Jeeps. Jeeps continued to use this transmission all the way through the 1990s, but to confuse folks the designation was changed to 30RH. If you google on 'Jeep 904 Torqueflite' it is fairly easy to get a picture.

You could not use the whole trans, since the Jeep trannies use a main case with the 'GM small' aka 60degV6 engine to trans bolt pattern. I am assuming that you could however harvest the Jeep TC adapter and short output shaft and graft them onto a slant six main case.

In Jeeps the 904 / 30RH was used mostly behind the 'AMC' 2.5L four cylinder engine.

That is all I think I know.

Piper106

Very Useful information. Thank you. Right now I'm trying to recover from a neck sprain I got at work, so I can't even get the trans back in the stinkin' car! And to top it all off my dakota trans is making death noises so this project will probably be put off for a month or so....
Thanks a lot though a short output shaft will make this job easier!

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72 dart acquired 12/08 /6,holley2b, mopar perf intake, mopar perf header, cam, built motor,904 finally re-installed, 8.75....still needs sorting out.
99 dakota 318 5 speed reg cab picked up 9/09; Trans finally fixed! woohoo!