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What transmission to run in your Ratrod, Chummins, Fummins or Other Cummins swap.



You are planning a cummins swap and now come to the question we must all ask ourselves "What transmission do i want to run?" Well this conversation is highly debatable depending on who you ask as everyone has their own uses and favorites. The purpose of this guide is to inform a future swapper of options and pros and cons along with cost for what we see. I will not be factoring in extremes ( sled pulling, drag racing, far over capacity towing, ETC) in any capacity as this guide is for the a weekend warrior average vehicle user. I also will not cover any none overdrive transmission. They arent worth the time to fool with, no one wants to run down the highway at 55mph at 2500 rpms.



The first big decision is are you wanting an automatic or manual transmission?


Reliability is a huge factor to alot of swaps and regardless what your trans builder told you while trying to selling you a built trans, a manual has much less parts to fail. There is no electronics to fail, no shift solenoids, valves, pumps, sensors or multiple clutch packs to burn out wiring to get frayed or computers to short out. There is nothing wrong with an auto and depending on needs they are better but from PURE reliability, a part cant fail if it doesn't exists. The famous engineering term comes into mind (keep it simple stupid). Technology has come light years in the last 30 years as far as auto vs manual, but most swaps arent on vehicles that are even 15 years or newer. If your building a ultimate survival rig or a bug-out-mobile, then a standard trans is the only logical choice. If you are building a 1 ton hauler  to pull a 32ft goosenecks loaded down multiple times a month then an auto doesnt seem like a strong choice without having to go deep into the pockets to build up the trans to handle that type of use, where most manual trans can handle this with no issues. Now if your build is a daily or family use vehicle, then an AUTO is a common choice. slamming gears in traffic is no fun and lets not even talk about trying to get the wife to shift gears if your like me. Even pulling your 5th wheel camper multiple times a year a long trips, isnt the same as heavy heavy loads weekly for your trans. Just take your use into account when selecting below.


I will rank the transmissions in order i believe is the most practice for most factoring in availability, budget and overall popularity from inhouse sales.






Manuals



#1  Nv4500- 5 forward gears


Average cost: $500-2200 depending on trans vs complete kit.

Adapter needed: No, factory dodge cummins 94-02 flywheel housing

Pros: No adapter, cheap to repair, widely available, wide choices for Tcases

Cons: 5th gear nut, 3-4 gear gap when towing heavy, expensive fluid

Overdrive ratio: .75

This trans is undoubtedly an easy and strong choice right out of the gates. It is cheap to rebuild, all parts are still widely available in aftermarket support, they are not overly large so they can fit in tighter trans tunnels and have been used in Gm applications from 93 and dodge from 94 until the 2000s. Now your like "but wait, my uncles, cousins, best friends, step dad said his 5th gear blew out and they suck." There is no denying that lots of prominently  dodge diesel nv4500s had 5th gear issues with the nut coming loose. Is this a big deal? Yes and no depending on how you look at it. If you have an nv4500 with a non-updated 5th gear assembly you are living on borrowed time to having a 5th gear problem, BUT WHAT HAPPENS THEN you loose 5th, and can still limp home. I have driven a good ways in the past when i have had this issue. You are not stranded and needing to call a tow just to get home in 99% of situations that are encountered. The first fix to this issue while in the truck is to add a locking 5th gear nut(under $50 depending on option). This is a good help and prevents it for most stock owners. If you already have the trans out while working on your project i suggest you dropping the money and going ahead and getting an updated main shaft($150). They are fully splined and have grooves that use a locking type washer to prevent the nut backing off, simple and effect, DONT WELD IT. The other issue that can be seen is stripping the 5th gear counter shaft teeth off, if you dont lug the trans and let your RPM drop them hammer on it, you have a lot better chance of this never happening.


#2  Nv5600- 6 forward gears


Average cost: $1300-3500  

Adapter needed: No, factory dodge cummins 94-02 flywheel housing

Pros: No adapter, no 3-4 gap so excellent towing capabilities, beefy internal build

Cons: Cost to purchase, cost to rebuild/ find parts, overall availability,

Overdrive ratio: .73


If your main goal for your cummins swap project is for a heavy hauler, then this is for sure a good option to check out. The transmissions is right around 400lbs which is double the weight of a similar nv4500… When comparing the parts between them there is literally no comparison. With this all being said, the transmission is not a top load transmission and this isnt a trans for the average guy to try to rebuild himself. The parts are getting hard to find and aftermarket support is almost nonexistent for anything more than wear items. Dont let this worry you, if you have a good trans and you take care of it, you should have thousands of miles and years of service with no issues… Just keep an eye on your fluid level and adding fast coolers is always a good thing.


#3  G56- 6 forward gears

Average cost: $2500-4000

Adapter needed: No, factory dodge cummins 94-02 flywheel housing

Pros: No adapter, shifts very smooth, still in production, parts availability, fairly strong

Cons: Cost to purchase, cost to rebuild, known for cracking the main case

Overdrive Gear ratio: .74 or .79 depending on year

These transmissions have been used from 2006 on in the dodge cummins trucks and are currently still available which is a testament within itself. The case of the transmissions including the integral bellhousing and case is made entirely out of aluminum  and while they are known for cracking in the case, with as many units out on the highways daily, it doesnt seem to be extremely widespread. When considering a g56, just understand they are made by mercedes and we all know how that goes for parts… Rebuilds are extremely expensive with some places quoting 4k plus and just a syncro bearing kit runs almost 1000$ by itself. This isnt to take away from how beefy this transmissions is as it can hold up to thousands of miles of high torque with the newer 6.7 common rail. They are one of the smoothest shifting transmissions and feel like going thru better between gear, If your going for a high end swap, this might be the trans for you.



#4 Ford ZF6- 6 forward gears

Average cost: $1500-2000

Adapter needed:  Yes a custom build adapter $600-1000

Pros:  Widely available in both the 7.3 and 6.0 power stroke trucks, large beefy trans, fluid cooler/ oil pump

Cons: needed adapter and cost along with it, cost to rebuild is high vs similar units

Overdrive Gear ratio: .72


I dont have any hands on experience with the zf6 transmission BEHIND the cummins powerplant. However in my early days of auto repair and service , I worked on many many fleet trucks with the zf6 transmission. BASED soley on my personal experience i dont like the shifting layout of the trans, and i feel like it shifts like a bulky leviathan. The independent dealer i worked for at the time commonly bought f350-f550s as service trucks to restore and requip other companies with them so i had lots of hands on interaction with them coming off the orginal fleet owners with 175k- 200k miles, a common mileage for trade in for new trucks. In that time i saw a high number of them with high levels of syncro wear at these miles. Having gone on in life to have my own employees that drive our company trucks, i do realize that they are not driven as you would a personally owned vehicle, but regardless there was in my opinion too many failures for such a robust transmission for that mileage. We had an issue finding a competent transmission shop that could handle the uniqueness that must be involved with rebuilding them as most shops wouldnt even touch it. Still to this day, we know many trans shops that wont touch them and will just sell a reman from a couple large companies. Taking this into account with the adapter plate, it completely dismisses the idea UNLESS you already have on in your F series project.






#5 Ford ZF5- 5 forward gears

Average cost: $500-1500

Adapter needed:  Yes a custom build adapter $600-1000

Pros:  availability from 7.3 powerstrokes, somewhat stout transmission if you have one

Cons: needed adapter and cost along with it, cost to rebuild is high vs similar units

Overdrive Gear ratio: .76/.77


Alot of the same info is a direct transfer from the zf6 in my opinion. I saw lots of units under 200k needing rebuild from syncro failure. The cost of the adapter adds to the cost, along with just like a zf6 finding a transmission shop to rebuild it completely should remove the idea from your search UNLESS you already have on in your Ford truck your swapping, Everyone else look somewhere else.


#6 Getrag G360- 5 forward gears

Average cost: $750-$2000

Adapter needed:  No, Dodge cummins 89-93 flywheel housing

Pros:  They come with the cheaper 1st gen trucks, Smooth shifting

Cons: Parts are non-existent and incredibly expensive if you can find it. Doesnt hold power well. 2nd gear syncro hub cracks, small mainshaft bearings. Top covers crack and wear out faster than others


There isnt alot of good things to say about a getrag other than they shift really smooth when they work. They dont like heavy weight or alot of power. If your donor came with a good shifting unit, then unless you are on an extremely tight budget, sell it and go with something better. No reason to spend so much on your swap and use something that WILL fail, unless you are running mostly stock truck with not alot of heavy towing







Automatics


#1 Dodge 47re - 4 forward gears

Average cost: $500-1000

Adapter needed:  No, factory 94-02 dodge cummins flywheel housing

Pros:  They are widely available due to wide production, cheap to upgrade and beef up, cheap, can use dodge factory PCM to control it, No expensive computer, Easy to DIY rebuild

Cons: weak in stock form, controller is about $800 if you cant wire up the dodge PCM yourself

Overdrive Gear ratio: .69


BUT DODGE AUTOS ARE WEAK WHY WOULD I WANT ONE?!?!?!?! Yea, They were underbuilt for what the cummins was putting out, BUT most last to around 200k for, what we see here on stock trucks.You throw in some injectors and a tune on your 200k mile trans that has never been serviced and are all surprised when it breaks.  Just putting a better torque converter with a transgo shift kit does WORLDS for what this trans can handle… I have personally rebuilt both 4l80es and 47RE/RH and there is nothing that significantly makes the 4l80e any better in my opinion . Everyone always tries to compare a Vortec 454 and 12v as the stock HP was very similar. I don't know anyone that keeps their project stock, BUT even so, Peak torque at 1600 VS peak torque of 3200 of a 7.4 is like comparing apples to oranges. If you want to go further, parts to upgrade are extremely affordable.  We have used these in numerous swaps with no issues. The wiring for the 47re pcm is very straightforward and allows the use of the obdII port for troubleshooting or there is several aftermarket controllers for both 47re and RH


#2 Dodge 47RH - 4 forward gears

Average cost: $750-1500

Adapter needed:  No, factory 94-02 dodge cummins flywheel housing

Pros:  cheap to upgrade and beef up, cheap, Can be run on toggle switches for overdrive and lockup if you dont want a controller,budget friendly controller prices Easy to DIY rebuild

Cons: Weak in stock form, needs an aftermarket controller to function as factory, Only available for 94/95 so they are getting hard to find and expensive. Certain 47RH specific parts are discontinued and hard to find.

Overdrive Gear ratio: .69


Same as above




#3 GM 4l80e- 4 forward gears

Average cost: $300-700

Adapter needed:  Yes, custom adapter needed

Pros:  cheap to purchase as it comes in thousands upon thousands of vehicles from the factory.

Cons:  Will need an engine adapter, aftermarket controller, and correct torque converter for the cummins. If you are upgrading your engine, will also need to upgrade the parts in trans.

Overdrive Gear ratio: .75


In no way shape or form do i hate the 4l80e transmission. I think it is a great trans for alot of vehicles, HOWEVER i dont think the cost for the parts needed makes it a very good candiate for anyone…. Adapter and flexplate ($1250), controller($700), torque converter (500-$1200). That is a huge amount of money that in my honest opinion could be spent beefing up a 47re to make it handle much better. This is before you even talk about the work needed for a mild build cummins in the 4l80e. “But they can handle 500HP LS no problem” Yup, but a 500hp LS doesnt even have 500 ftlbs in torque, where a cummins with just a mild tune is right at that.. .EXCEPT AT 1600RPM… it isnt


#3 Duramax based Allison 1000- 5 or 6 forward gears


Average cost: $800-1400

Adapter needed:  Yes, custom adapter needed unless attempting to run SAE3 housings from an industrial engine

Pros: Double overdrive on 6spd models, Fairly robust in stock form

Cons:  Extremely expensive to adapt to the cummins ($3500)Will need an engine adapter, aftermarket controller, and correct torque converter for the cummins.  Mechanical motors dont have additions for torque management that makes the allison so successful behind duramax trucks. Overdrive Gear ratio: .71 on 5spd .61 on 6spd


Everyone who talks about a super truck build always talks about a an allison cummins combo and why they didnt do that from the factory. My knowledge on the cummins allison combo, comes from a few knowledge diesel builders in circles im in along with a few people i have talked to in the past, that have actually done this swap. The biggest issue is while the allison is somewhat robust, without the assistance of torque management to lower engine power output when it goes to shift, it isnt as durable in stock form that it is all cracked up to be. This can be overcome like any trans, but mild rebuilds on the allison are 3-5k all day and the sky's the limit for the high end.

Double overdrive is great, and i wouldnt consider doing any allison swap without using the 6spd to get this. If your going all out and money isnt an issue, just telling everyone you have an allison might be worth the cost to you, but to most, it just isnt worth it.