Well I did some searching on the subject after reading what dan had to say in the recent discussion on overdrive transmissions. Found what is supposed to be a good volvo m46 with the rear planetary bolt on overdrive here on ebay for 300 bucks. Doesn't seem bad as a start toward an extra gear on a 904, you could probably get one from a local salvage yard for less without the trans attached.
Sent a p.m. to Ceej so I guess we'll see how realistic this is.
I'd love to have a 4speed 904 without spending thousands myself.
WOW. Just saw gearvendors wants $2700..
Might be onto something here...

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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!

From what I remember that IS the gear box that the gearvendors box is based on. The bad news is they will not sell you just their special adapter to make that OD box work by it's self behind your trans. I remember a discussion somewhere about this several years ago, that GV won't even talk to you about "parts" unless you have a serial # for one of their units.

That was several years ago, but I think I am remembering it correctly. I am sure that Volvo box could be made to work, WITH enough time, fabrication and machine work, but would it be worth the money it would cost? Would a machine shop be scared of stepping on a GV patent in todays sue happy society?

Let us know if it works, might be an easy way to put 5th gear behind an 833 4 speed. Lots of junk Volvo's around here.


TopHat

Yea the laycock overdrive design is the basis of the gearvendors unit. Gearvendors actually produced over a million units for volvo oem use before GNK took over. The link in my first post is to Maximum Overdrive, who manufactures just such adapter components without raking you over the coals; forcing you to buy an all new O.D. unit.
I guess I'm going to email them about an input shaft to a chrysler 904 and dimensions for an adapter, since I could weld one up cheaper than having them design and cast a new one.

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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 Volvo M46 is an excellent OD. The ones that dont work usually need a filter or wire harness work.

It might be easier to adapt the 4 speed trans in front of the OD at the same time.....The 4 speeds in the six cylinder cars were pretty sporty and strong.

If I were to put a m46 behind a 904 I would consider to do it like a divorced transfer case....with a short drive shaft. Mount the OD on its own crossmember/subframe.

Another way to do this is an underdrive. Is there a bolt on 4x4 transfercase for the 904? It would not be difficult to lose the chain, lower shaft and lower case on a NP208 or similar. A modern transfer case low range is just a planetary shifted by a fork. You get a 2.5:1 reduction.
2.2 on the highway 5.13 at the drags.

I built an adapter once that put a NP208 behind a 2wd TH400. The case was locked in 4wLOW losing lots of pieces. A 208 minus extra parts would weigh about 40 lbs. I made the dapter out of 1/4" steel welded into a box. Before welding we cut out the openings for the trans and TC as well as indexing the mounting holes. It took about 4 hours. Im sure a 904 would be similar.

I actually have a DeSoto project here that was to have a 727/ Ford 3 speed manual underdrive. !st and reverse were removed from the case . It was fork shifted. Its another steel box case adapter. I used a clutch disc hub for the shaft adapter. I started that project in 1997. I have since decided to go A500.....

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

Maximum overdrive makes all the components for doing exactly that.
Interesting! Seems like 4wd 904s exist... Need to look around to make sure.

I guess I just liked the idea of bolting it on, they make the custom input shafts, then there's only one driveshatf to mod .

I really like the 4wd case Idea though. Need to see what the lowest gear I can put in my 8.75 is. Thanks sandy!

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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!

Actually with the underdrive you want a higher gear.

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

ahem... Sorry, numerically lower.
anyhoo, here is a t-case adapter for a 904:
http://cgi.ebay.com/ebaymotors/Dodge-Je ... 3a54ad4b96
Which honestly has me thinking about the volvo unit again, attached with a flat steel or aluminum plate and a max. overdrive shaft.
Emailing them now. Email sent.
Sandy what about shifting the t-case? Just the normal routine- Stop- Neutral- Pull lever- Shift back to drive?
Maybe a push-button t-case for on the fly shifting with no extra levers?

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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!

Shift on the fly is not likely.......they are not made for that. You should be able to shift your 904 to neutral and then go from low to high.....then 904 to Drive....at about 70 mph

Look for the TC with the smallest ratio ..look for one with a planetary reduction gear. Gear reduction TCs are heavy and noisy.

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

From QUAD4x4.com:
From 1980 to 1987 Dodge used the two speed, NP208, chain drive, aluminum transfer case in all Ramchargers, W150 and W250 trucks. While not a particularly robust design, the 208 generally gives good service unless abused or poorly maintained. The 208 was the first New Process production transfer case to use a planetary gear low range. The low range ratio is 2.72:1. Early units from 1980 to 1982 were not synchronized. Late 1982 to 1987 208's in Dodge trucks are synchronized for 4 wheel drive.

So I'm gonna start digging to see if I can find anNP208 from behind a 904!

Question: would a v8 904 and /6 904 have a different # of splines on the output shaft?

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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 keep on spacing this! Sorry guys. Been an impossible busy weekend.

I just left a message on Wayne's phone to see if he'd made progress on the adapter. When he calls, I'll put an update here.

From what Wayne told me, the Volvo unit is made by the same folks that make the Gear Vendors unit. The differences are enough that parts don't interchange.

CJ

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Part of Tyrde-Browne Racing

Lack of interchange with GearVendors' stuff wouldn't be any hassle at all; the Laycock overdrive as used in Volvos for many years is well supported with repair parts and service kits, etc.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks Ceej, really appreciate it.
Also I'm having trouble locating an NP208 on the interweb. The newer cases are ridiculously easy to find.
Thanks for everybody's support on this.

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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 am watching this thread with MUCH interest. Especially the bit about swapping the 4X4 transfer case onto a 904 for overdrive.

Underdrive.
I don't mean to be confusing, but when sandy brought this up I knew I had to investigate. I think both options could be made to work well; though honestly I think the t-case underdrive would be better suited to a manual trans car. Then it would just be like shifting into fifth...
Whereas the volvo/laycock/gnk overdrive I believe could be set up to be completely automatic.

Add in the fact that I have 3.55s in the 8+3/4 and I think the overdrive would work better. That would be a 2.77 highway cruising gear.(Volvo O.D is 0.78 thanks josh)
With 3.55s underdriven via t-case I would have a 9.59 (holy crap!). So a rear gear swap would be necessary.

What's the lowest numerical gearset ratio available (stock) for an 8+3/4?

I've already shown that an adapter exists for the 904 to a t-case...
just not 100% that its a 208 case which that Particular adapter would mate up to.

Sandy has already shown that its doable to gut the case for this purpose, so I guess all that's left to do on that option is find a 904/208 4wd truck in a junkyard for proof of concept.

And on the other side we'll see if Ceej's friend has an adapter worked 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!

2.76 is the numerically lowest gear available for the 8 3/4. If you wanted to go real slow with huge tires then underdrive would be practical. The Gear Vendors ratio is .78:1 and I believe this is the same as both Volvo OD units.

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Joshua