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Discussion Starter #1
Hey guys working on a custom project with an old dodge 4dr dart... looking for the best 4wd manual transmission for a modified 4bt... I have a np208 t-case in waiting... wouldn't mind using a 205... but I need to figure out what's the best trans to use... looking for a 5spd for the highway econ...
 

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Maybe start by telling us it you currently have an adapter plate for your 4bt...

Highway economy and 4x4 don't mix well...

The common manual transmissions are found Ford and Dodge chassis. The GM bread vans usually came with an automatic transmission, manual transmissions in a GM product were extremely rare. There are a few SAE bellhousings in existance, again rare.

The 4bt does not come out of the Cummins factory with a bellhousing. The adapter plate, flywheel, clutch, bellhousing, transmission, started and required fasteners are mostly unique to each manufacturer.

In general, the cheapest way is to source all of the above parts together, one part at a time gets very expensive.

I used a Ford M5R2 (a.k.a. M5OD) 5 speed OD transmission, as it bolted up to my Ford adapter plate and used my original clutch (still working after 70+K miles). Down side is the internal slave clutch (concentric to the trans input shaft) leaks after 2 - 3 years. Removing the trans is a big pain.

Maybe look at a 5 speed overdrive trans form a 6bt Dodge truck?
 

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Highway economy and 4x4 don't mix well...

Maybe look at a 5 speed overdrive trans form a 6bt Dodge truck?
I agree with Russ on the Dodge 6BT tranny. The first generation Dodge Cummins used the Getrag 360 with an NP205 married to it. I have no problem with mine. As for "economy and 4X4 don't mix", I disagree a bit. I have this setup in my 91.5 Dodge Cummins 6BT W350 (All stock except 4" SS exhaust). I'm dragging 7500lbs around empty and getting 25+mpg highway running 62-65mph (Yes I'm cheap and drive slow like an old fart for better fuel mileage). I have manual hubs up front, the stock 215/85/16 tires and 3.54 rears.
I think the smaller 4BT in a lighter vehicle should compare unless you get into a taller tire which equals more inertia to get rolling.
Not sure the availability of the Getrag 360 setup, but you probably would be able to source parts for the later and better NV4500 tranny. They both have OD which is what you want.
You can check them out here.
 

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One question would be how modified will the 4bt be? As Russ mentioned, the M5R2-OD transmission can be very good if not abused. It has excellent gear ratios for the 4bt but isn't unbreakable. We have members also using the ZF S5-42 transmission with the small block Ford pattern. Not quite as good in the gear ratios there, but very strong. A better ZF would be the one from behind the 7.3 diesel in the F250/350 trucks. Has better gear ratios and an external slave cylinder, but will cost in the neighborhood of $1500-2000 to fit it to a Cummins. The NV4500 from the Dodge is strong enough but doesn't have the best gear ratios either. It winds up being used a lot because of cost. If you're doing 4x4, the Ford transfer cases were all driver's side drop. A NP205 can be matched to those transmission. The Dodge can go either way. Their NP205 was passenger's side drop and later switched to a NV241 which is driver's side drop. Of course there are other transmissions but these are some of the most commonly used. The Ford ZF 6 speeds are a possible as well as the Dodge NV5600 or G56.
 

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Discussion Starter #5
Thanks guys for your responses... I'm doing a custom 4dr dodge dart on k5 blazer suspension... since I'm going whole hog on suspension mods and custom frame work, I figured it would be bad ass if I could drop a 4bt in there
 

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Discussion Starter #6
I have a 700r4 from the blazer that has been built at one point but I have to rebuild it before I put it in anything...will that trans fully built handle the torque? I'm doing this all at home. If I was dropping a gasser In, I wouldn't have a problem, the diesel is slightly new territory.. I've worked on big diesels but never a 6bt or 4bt... I've watched videos on different turbos and the injection pump tuning... and that's probably as far as I will go in the future with performance ... nothing crazy... just decent boost and nominal performance...
 

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The 700R4 doesn't have the best reputation behind a 4bt. A couple issues show up that can be death to that transmission unless it's built to handle it. First is the fact that the 4bt hits full torque around 1700-1800 RPM. The gas engines hit that about 1000 RPM higher. That transmission was used on some GM diesels but they generally were higher revving than a Cummins. What happens is the pump in the transmission doesn't get full pressure to the clutches and you get burned clutches. Also, that transmission is basically a TH350 not nearly as strong as the TH400 series. From my understanding there were 2 models of the 700R4 and one is a better option than the other. Whatever auto transmission you use, you'll need a torque converter with a stall speed around 1300 RPM. You choice of transmission may depend on the engine you find. The road engine came with either a GM adapter plate, a small block Ford adapter plate, or an SAE2 or SAE3 adapter plate. Virtually all the GM's were auto where the Fords were manual. The SAE's were on the Eaton manual and the Allison auto transmissions. Anything else will require some type of aftermarket adapter. Virtually any transmission that can live behind that engine can be adapted.
 

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I'm doing a custom 4dr dodge dart on k5 blazer suspension
Uhh, why would yu want to do such a thing? Granted, they're your vehicles and you can do whatever you want with them, but both are vintage iron that aren't being made anymore. Especially in the case of the K5 Blazer, so many have been junked turning them into rock crawlers that end up quickly being destroyed and scrapped. They're actually getting pretty scarce. Likewise, old Darts don't exactly grow on trees anymore either and even slant 6 darts are becoming more valuable. Please consider that before going down a road that will more than likely end up with both vehicles being scrapped.
 
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