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Alright guys. Thanks to a bunch of help here I’m getting pretty close to having all my plans somewhat finalized so I can continue with the build. I’m putting a 4bt in a 2001 Durango. I have been planning and still am for now on a g56 transmission. So my plans for this Durango is to travel around the us and Canada hopefully months at a time. Mostly tenting at first but eventually pull a medium size travel trailer. Also some off-roading along the way, nothing extreme but want the option. My goal is great fuel economy. What would be the absolute best transmission? I would like a double overdrive or even a 7 or 8 speed to keep the engine at 1800-2000 rpm whether I’m cruising at 50 or 80. There is a getrag t56 made by rock land standard gear. I’m assuming it’s pricy and no adaptor plate that I can find to an b series. Any of the Eaton fuller 8 speeds will be too big and heavy to be practical right? Is there anything better than the g56 that is practical?

What flywheel housing, flywheel and clutch would you recommend? Thanks guys.


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That last word "practical" pretty well sums it up. No Eaton unit is going to fit and their manuals didn't offer a double OD. They did do double OD in the automatics, but there you've got physical size and a 4x4 application against you. Probably the only sort of practical double OD would be the Allison 1000 6 speed that comes in GM diesels and those aren't tiny either. Automatics in general will not be as fuel efficient as a manual. Main thing will be to get your axle gear ratio and transmission so you can change gears on the stick and maintain optimum RPM. Even with the G56 you have to decide which one. 2005-2007 had one set of gear ratios and 2007.5 and up were different. Might do some calculating on those ratios to see if one fits a 4bt better.
 

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Discussion Starter #3
I’ve checked them both out. The earlier one would be better suited to pulling the trailer and the later one would be better for everything else.


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I would use the nv5600 over the g56. The ZF6(650/750)is better than both of them IMO. Topkicks and Kodiacs had a 6sp ZF as well without the married bell housing. No need for double overdrive if properly geared. I ran a G360 and a brownie(DOD) because of a 4.11 rearend. A 3.54 or better a 3.07 and 34s would be ideal. The less links in the chain to break, the better. My 2c
 

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Red, most of the Dodge guys would argue that the G56 is far better than the NV5600 which it replaced. I'd agree the ZF is probably a better transmission. Main issue there is the cost of the adapters which will run near $2000. Even the ZF diesel 5 speed is very good but the adapter part hits that one too. Then you have to work out what transfer case. Any of these transmission may require some tunnel work as most of them are quite large. The ZF 6 speeds also require a transmission cooler. No simple solution to the problem. Can kind of see why a lot of the Durango swaps used the A518 or A618 automatics. They came behind the 6bt , are plenty strong enough for a 4bt, and are reasonably cheap to adapt. Most of the manuals we see swapped are the NV4500 but that one has poor gear ratios for a 4bt. It's just cheap and that usually gets the nod.
 

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Looking back with hindsight I would have been light years ahead by going with the ZF diesel and ALL it would have cost in the beginning, but seeing as my engine came with the Ford/Cummins adapter I took the path of least resistance...............LESSON LEARNED.................$.02
 

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Red, most of the Dodge guys would argue that the G56 is far better than the NV5600 which it replaced. I'd agree the ZF is probably a better transmission. Main issue there is the cost of the adapters which will run near $2000. Even the ZF diesel 5 speed is very good but the adapter part hits that one too. Then you have to work out what transfer case. Any of these transmission may require some tunnel work as most of them are quite large. The ZF 6 speeds also require a transmission cooler. No simple solution to the problem. Can kind of see why a lot of the Durango swaps used the A518 or A618 automatics. They came behind the 6bt , are plenty strong enough for a 4bt, and are reasonably cheap to adapt. Most of the manuals we see swapped are the NV4500 but that one has poor gear ratios for a 4bt. It's just cheap and that usually gets the nod.
I disagree Char, west side Dodge guys have a differing opinion of the g56. From what Ive gathered from tranny builders the 5600 isnt light or shift like a car but seems more durable over time. The zf6s do require a cooler but thats about as simple as it gets. A snowplow 12V motor coupled to a Procon pump and a cooler into PTO weld bungs and a CAT 2 micron filter are plumbed into the nv5600 on my Ford. Will only run it when trannys warm but really dont ever plan on towing much.

Theres a member on this forum named Cody. He started making ZF6 adapters in Boise or Caldwell ID and started Wild Horse MFG. He seems to have made a name for himself. His adapters are 5-600 shipped. I dont know from personal experience but do have a ZF S6-750 from a 6.0 needing an adapter in the future.

Weight wise the G56 is better or the diesel zf5 for that matter in a durango.
 

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Problem with any of the NV transmissions is finding good parts now. Since NV went under, everything i've seen or heard for parts for them has been junk. Unless something has changed recently? With that said, the NV5600 is stronger than the G56 overall, due to cast body vs alum but the parts for a G56 are top notch vs the NV junk. Many guys have had to change out the NV parts like underwear, due to poor aftermarket quality.
My G56 is 14 years old, all original other than the SBC twin disc clutch & still shifts like butter. When the day comes to need a part for it, I know it will be top notch....not aftermarket junk.
 

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Good point Mark. Back in the day when the NV5600 was being built, good parts existed and there were a few fault with the OEM transmission that could be addressed. But now you are at the mercy of whatever is out there. The G56 is a Mercedes product and that company doesn't like the word junk attached to anything they make. It is a lighter weight transmission but super strong. Much in the category of ZF which is another German company. Their units have been in Ford and GM diesels and maybe even Corvettes in this country. They just aren't in that field anymore since the engines have passed their capacity. I believe the G56 is the only current diesel pickup transmission available. Of course any of these is more than adequate for a mildly powered 4bt or 6bt.
 

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Discussion Starter #11
Thank you guys. I had ruled out the zf earlier just cause it wasn’t used in the dodges. I know they make good transmissions. I had ruled out the nv5600 because of the weight of the cast case for one, and I’ve heard of shifting issues. My father-in-law blew the whole transmission when it went to reverse instead of 6th I think. It was many years ago. I will definitely check the ZF out. I was just comparing ratios from the g56 and the zf s6-650. Pretty similar. It brings up another question. I’ve driven a golf TDI for 10 years. I’ve driven a couple dodge trucks with a 6bt but not routinely. What sort of rps should I be shooting for for cruising? What would be lugging the motor too much. My TDI if I’m under 1800 I am easy on the throttle and rarely am under 1800 in the higher gears.


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I would want ~1,800 at interstate cruising speed in top gear, with a well matched turbo 1,500 is about as low as I like if I have a good load on the engine but ~1,300 if your not loading it is OK. It seems to me that the individual power stroke of each piston becomes real noticeable much below 1,500 if it's under heavy power/loading, and I figure if it is being felt like that it's gonna be hard on things............$.02
 

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I own a 01 Golf TDI std & a 12v Cummins with a G56.....similar on the lug deal. As long as your not trying to apply too much power, the G56 is happy to cruise along at 1500-1600. But you will find the sweet spot of a Cummins is between 1700-1900 for best fuel mileage on flat ground, unloaded. Reason being is air through engine. Too low of rpm & the valves & piston flow isn't bringing in enough air to achieve the best fuel to air ratio.
 

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Mark is absolutely correct about the 1,500/1,600 at speed the 1,300/1,400 I mentioned was for driving in neighborhoods business districts or trails at lower speeds and engine loading's the 4Bt will run clean and cool there with a properly sized turbo.
 

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Discussion Starter #15
I found a nice schematic type drawing with all dimensions on it for the zf, but can not find one for the G56 I’ve searched and searched. Also someone here I think said the G56 has the starter on the passenger side, from the pictures I have seen and the manual it looks like drivers side?


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Starter is on the driver side and the adaptor plate for the G56 is the same for the NV4500
 
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