I have my own 12 valve Cummins to 68RFE swap in a 97 Dodge 3/4 ton. See a video of mine shifting with 1100 miles on it here. Email or call me for more specific information that applies to the swap you are considering.
This swap is intended for trucks with stock or mild power upgrades, not for high horsepower. It is for the guy that won't ever buy a new truck and likes the dependable 12 valve, or has a nice newer 5.9 but hates the 4 speed auto. If you are this kind of person and have a 89-07 5.9 Dodge Cummins pickup, consider swapping in a 68RFE transmission. Even though it is similar to the lighter duty 5/45RFEs it was made for the 6.7 Cummins diesel with 6 pinion planetaries and no band type clutches are used. The gear ratios are awesome for a light duty Cummins work or play truck, and since you can use a factory style flex plate and adapter there are no worries about issues caused by flex plates that don't flex, buying and wiring up different starters, or parts not made to proper specs. Not having to buy expensive aftermarket adapter parts (12 valve engines do require a spacer), different transfer cases, or driveshaft services enables the swap to be done on a reasonable budget.
The 68RFE is actually the same length as a 47 or 48RE, only the minimal difference in the factory adapter is the difference, so the stock driveshaft length works fine. If your truck is a 97 and older 4-wheel drive, a '99 and newer floor mounted transfer case shifter is the best way to go so mounting the older style shifter is not an issue. The input gear for your current transfer case will need changed, unless you have a 5-speed manual now- but they are reasonable and not terribly difficult to change. '93 and older t-cases won't accept the different input, a Chevy 241 passenger side drop case is an alternative. The mechanical shift linkage can even be used- I can provide a link to make it work.
On a side note- if you have come here looking for info on replacing a 68RFE with a 48RE, I can let you know that this requires a stand alone controller and custom valve body, so it is probably nearly as expensive as putting a Ford 4R100 in. I have to go on record for not recommending replacing a 68 with a 48. I have tuned a few of them for guys stuck with them and am not impressed with their performance. If you want something stronger consider a built Allison 6 speed, or a built 4R100 instead of the built stand alone 48RE.
PCS Control System Info
I am finally about finished the transition to the brand new TCM-2800 transmission controller made in the USA by Powertrain Control Solutions. Initially I had hoped to run the 68 to my high expectations with that controller by itself, however after extensive testing and development I have found that it will require another module I have developed that I call a TCS module (torque converter shift module). This module gives me the control I need for excellent shift quality, even with "lock to lock" shifts.
I may continue development and testing of the OEM control system now that EFI Live has 68RFE tuning capabilities, but it is doubtful that the OEM system tuned with EFI Live will be a better alternative with all the sensors and wiring it needs to operate.
The price of $1500.00 for the control system
includes the base calibration and tech support to get it installed,
the TCS module, and a fuse/relay box that provides all the relays
and fuses for reverse lights, neutral safety, and a few extra for
other options. This price does not include tuning, since
tuning requirements are quite variable depending on power and
vehicle use. Tuning support is provided at
$40.00/hr, so plan to spend at least $40 on tuning and up to $350 or
more if you need precise tuning or a tow/haul calibration in
addition to a normal cal. If we figure on $250.00 for tuning that
should give you a close idea.
A laptop computer is also required to tune, diagnose, and change calibrations – and you will probably have to call me if you have problems rather than your local transmission shop. I recommend using a Windows operating system, and the computer must have a USB port. While it may be possible to use Macs or Linux with the WINE program, Windows is best.
Fully adjustable Shift points/Lockups
Shift points are fully adjustable, and lockups can be enabled wherever you want them in 2nd through 6th. The control system unlocks the converter just enough during shifts just like a factory system so smooth shift quality and power transition to the next gear is maintained.
The 68 swap will work with an exhaust brake when the torque converter clutch is applied (locked up)- and I can tune the control module to lock the converter at zero throttle- so yes it will work with an exhaust brake.
The 2800 controller allows “Calibration B” to be enabled for all applications. This can be used to switch to a Tow/Haul tune with a switch or even your current cancel od or tow/haul switch.
Manual mode enables you to control the shifts completely and shift the transmission with a switch. Depending on your application, you may be able to use factory switches for upshift and downshift, or you may use aftermarket 3-wire momentary rocker or toggle switches.
Stand alone controller advantages:
After considering all of that information, you may agree that being able to install a used 6 speed automatic for $5000.00 or less is worth it. Improvements are constantly being developed so if you are not sure it's the swap for you check back in a few months.
The 47RE to 68RFE swap can make your 89-02 Dodge Cummins drive and haul like a new truck. Upgrading these older trucks is going to continue to be a serious consideration since the trend is to fix up an older truck that doesn't have all the emissions garbage to deal with. The 47RE is the worst part of these older trucks, infamous for poor shifting issues when cold, frequent band adjustments, overdrive problems, and an extremely high geared reverse.
To replace the 47RE with a 68RFE, my spacer is required (which enables the factory transmission adapter to be used), and the crankshaft pilot hole must be bored out with a tool that I have developed that can be used with your engine in the truck. It is also possible to use the 6.7 flex plate if desired, although the earlier flex plates can be used if a custom converter is built, or the center hole is bored out to allow the larger torque converter pilot to pass through.
The 6.7 adapter shouldn't be used on the 89-02 engines because two bolt holes are different that bolt the adapter to the engine. It's not possible to even re-drill one- and I wouldn't really recommend leaving those bolts out. Otherwise the 6.7 adapter does bolt on.
Replace a 48RE with the 68RFE
To replace the 48RE with a 68RFE, you can buy a 6.7 transmission adapter, it will bolt right on a Commonrail (except for the extra support brackets), or you can buy my spacer and use your current adapter. Having the torque converter pilot turned down or boring the crank pilot hole is still required for 05 and older engines, but according to what I have seen, all 06-07 Commonrail engines already have the correct crank pilot- and perhaps some 05 cranks do as well. It is possible to use the 6.7 flex plate if desired, although the earlier flex plates can be used if a custom converter is built, or the center hole is bored out to allow the larger torque converter pilot to pass through.
For those guys with 06-07 5.9 engines the 68 swap is arguably the easiest diesel trans swap out there. That's not to say it does not have it's challenges. Dealing with limp mode due to the missing 48RE trans is one of those challenges no matter what transmission you swap in- even a manual trans. 05 engines are more difficult and may require a manual trans ecm for sure. For the 06-07 models, it is possible to fool the auto ECM to think there is still a 48RE in the truck and one advantage to this method is that it allows you to keep your digital gear display in your dash. It is also possible to flash the ECM to a manual trans calibration and solve some of those issues, but it creates other issues of it's own. Another challenge is cruise control. It will still work, without any modification, but it will ruin your transmission, since the aftermarket trans controller will not be seeing the correct throttle position with the cruise on. I have dealt with these issues before and can assist you with sorting through those options.
It won't save you money, and it probably isn't any simpler or easier- but if you want a double overdrive, lower first and reverse gear, better factory torque converter stall, and OEM adapter components, using the 68RFE in your Cummins conversion is definitely something you might consider. It's best to use a hybrid transfer case. A 271 or 273 (electric shift) Dodge front half and Ford rear half is the high class. This allows you to keep the fixed yoke and electric shift controls if your transfer case is electrically shifted. Be prepared for driveshaft modifications, but often you need that anyway with a Cummins conversion. If you are using a 6.7 Cummins, I would recommend using the 68RFE for sure.
The crankshaft or torque converter pilot will need to be modified (unless you are using a 05-2013 Cummins) and you will need a spacer if you are using a 89-02 Cummins.
There are some very loyal 47RE fans out there on the forums that like to say that the 47 or 48RE is the greatest trans that ever was and the 68RFE is a weak trans. Personally, I don't know why anyone besides racers that have a shed full of spare parts for them like the old school RE. The guys that are swapping out the 68 for a 48RE are those that have gobs of horsepower and will most likely break whatever is behind their engine sooner or later. These swaps require custom valve bodies and control systems as well, so it costs more than a guy thinks.
The 68 is a much better design and when compared
stock to stock is much stronger than the RE transmissions. It was built for the 6.7
Cummins making 350 hp
and 650 ft/lbs of torque, even up to 800 ft/lbs of torque starting
in 2011. So the stock 68RFE was at least built to handle
as much or more torque than a stock 48RE, and it does in the
thousands of 07-14 Dodge Cummins trucks on the road today. The
problems guys have had with it I believe are due mainly to stock
transmission tuning behind high performance engines. Sure you
can pay big bucks and get a 48RE built to handle more than a stock
68RFE, but it may make sense to put that money into a better trans
to begin with, especially if you are leaving your Cummins power
stock for good fuel economy and dependability. There are companies building performance upgrades for the 68RFE now,
and with the 6-speed Allison option available too it may be the time to leave the old 4 speeds behind
for your everyday work truck. If you are a racer, I would
recommend a Ford 4R100 over a 48RE any day.
Don't misunderstand, if you have a high performance Cummins (over 400 hp) you are better off with an Allison or 4R100- the 68RFE may handle 450 or higher but it's probably not be worth the risk unless you just want to throw a cheap stock trans behind your performance Cummins and take your chances. If you are under the 400 hp mark the 68RFE is probably going to be just fine, providing you take care of it and get it tuned well, just as you would need to do with any transmission. I promise you will like the gear ratios. That's my two cents, take it or leave it. If you still don't agree, it's ok with me- keep your 4 speed and it's sluggy reverse☺. Shifting to 4 low if you have it does help a ton when backing up a heavy trailer.
All the teasing behind, I do realize a swap is expensive, rebuilt transmissions are expensive- and new trucks are very expensive. All any of us are trying to do is make a living and hopefully have just a little fun and less stress doing it. Many of us depend on our trucks every day to earn a few dollars, and they need to be the best they can be.
The later model 68RFE transmissions (part numbers under the bar code ending in "AE" or "AF" on the sticker, or the same last characters on the stamped code just under it on the case) got some upgrades to the valve body - so these are the best transmissions to purchase for a swap. As far as I know the only difference to the '11 and newer model that handles 800 ft/lbs is the converter and the factory tuning.
One more durability question to address is case cracking. There have been more than a few instances of this happening, and the general consensus is that it is caused by bad vibrations due to bad u-joints, worn extension housing bushings (the bushing that supports the slip yoke of the rear driveshaft) or bent or unbalanced driveshafts. It may help to install an aftermarket aluminum oil pan and definitely don't ignore any bad vibes. It is worth pointing out that the 47/48RE has also been known to crack as well and Allisons too. Even 5R110s have had case problems. Now in all fairness, if the case cracks on one of these transmissions it probably is currently cheaper to repair than a 68- but the point I'm making is all of them have potential to crack if subjected to the wrong stress.
Locking the torque converter in lower gears and shifting to the next gear locked can help get more power transfer to the ground where you need it. This type of transmission tuning is commonly desired, especially when there is a monster under the hood- and the 68RFE especially shines with lock to lock shifts due to the close ratio gaps. There are valid concerns however, that doing this with the 68 can cause clutch slippage. This did was proven to be true with my first high performance customer using my old control system. He was using a 68 with clutch and pressure upgrades, basically everything available except for the M3GA drum- and did have a 5-6 lock to lock slip likely due to the shock of the shift.
This problem of lock to lock slip and the other side of the fence - damage to input shafts, drums, and converter hubs led me to develop the TCS module, which unlocks the converter very precisely according to load during the shift, and re-applies it so quickly and smoothly that when adjusted specifically for your application makes lock to lock shifts as smooth as a normal shift. This controlled slip has to be very precise, too much slip and the converter clutch could be damaged or shift quality will suffer, not enough slip and the shift is too shocking to the system without employing a slow slushy shift.
See my transmission swap comparisons page for more info on other transmissions and how they stack up to each other.
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