68RFE vs Aisin Seiki • The Full Length In-Depth Comparison

Table of Contents:

- Introduction to the 68RFE vs Aisin Seiki
- Overview of the 68RFE
- Pros of the 68RFE
- Cons of the 68RFE
- Overview of the Aisin
- Pros of the Aisin
- Cons of the Aisin
- Can I perform a conversion from 68RFE to Aisin or from Aisin to 68RFE?
- The Conclusive Answer


Introduction:

     Let’s face it. Mopar does not have the best reputation for transmissions; especially in the big diesel truck game. In recent years, the 68RFE, AS68RC and AS69RC have all been unique transmissions available to outfit our 6.7L Cummins with the right platform for our needs. Naturally, this raises some questions:

- 68RFE or Aisin, which do I buy?

- How can I tell which one I currently have?

- Am I f*cked if I bought one or the other? (You know you’re wondering)

- Can I swap from one to the other?

- How much power can each handle from the factory?

and more!

     To say the least, all of these transmissions have a time and a place. There is no specific answer as to which is undeniably the “best” and which is undeniably the “worst”. Henceforth, we will present as much information, education and objective science as possible to determine just where these transmissions stack up. To start, we must look at each transmission individually and understand a brief amount about it’s origin and intended application.

*Queue the drum-roll please*

Overview of the 68RFE:

     This transmission was introduced in 2007.5 as a successor to the 48RE during a time when Ford and General Motors were producing 5 and 6 speed transmissions respectively. 68RFE trucks can be identified easily because the transmission oil dipstick is on the passenger side of the engine bay. Despite all of the impending doom the 68RFE and it’s abysmal valve body bring forth, it is a powerfully reliable transmission after being properly built.

     But, in stock form, it cannot hold much more than factory power. In fact, it just simply crumbles. The torque converter cannot withstand the torque, the valve body wears out very quickly, it simply needs a lot of love to succeed. An excellent place to start is with an affordable valve body upgrade kit like our Project Carbon™ 68RFE DIY Valve Body Upgrade Kit.

Pros of the 68RFE:

     This transmission has the most aftermarket support of any of the 3 transmissions. Whether you’re looking for TCM tuning, or you’re looking for the ultimate 68RFE valve body, our Project Carbon™ 68RFE Billet Valve Body, the aftermarket support and knowledge is there to make the moves happen. This is rather unique to the 68RFE when compared against the Aisin Seiki relatives, as we will discuss later in this technical publication.

     A final benefit to the 68RFE that may be relevant to some consumers is it’s fast shift speed compared to the Aisin. This is because the 68RFE does not necessitate as much of a fuel de-rate during shifts to facilitate a safe and properly timed clutch to clutch transition. For more information on “fuel de-rate”, keep reading! Keep in mind that none of these 3 transmissions have bands or servos, and rely strictly on solenoids to control clutch to clutch timing. Pictured below is what happens when poor clutch to clutch timing occurs.

*Pictured above is a set of burnt overdrive clutches from a 2019 68RFE. For a more in-depth read on the 68RFE and it’s unique ailments, try reading “Transmissions 101: 68RFE Valve Body Problems, Solutions & Upgrades”

Cons of the 68RFE:

     The 68RFE has more mechanical, electrical and hydraulic problems than one could ever attempt to recount. Justifiably, I will focus on it’s largest shortcomings.

     The first of many is that the transmission is incredibly expensive to manufacture for high performance applications due to the fact that nearly all of it’s internal componentry must be reengineered from the ground up to succeed in this environment.

     In fact, an unmodified 68RFE will usually die within a few thousand miles at 400HP+ and tends to die instantly much beyond that. Various factors come into play such as Torque Multiplication Factors; you can see our full guide to those here!

    In short, once power, mass or tire size is added, the 68RFE transmission quickly begins to suffer. We should remember that this transmission is an inflated version of the 45RFE, found in the Plymouth Caravan. The overdrive assembly is almost identical!

     Where most transmissions can be upgraded to reliably support the average tuned truck for about $4,500, a well designed and manufactured 68RFE for a tuned truck that checks all of the boxes for “probable or eventual failures” will likely cost more like $6,000-$7,000. Our “SuperStock 68RFE” is a wildly popular option for someone in that price range.

Overview of the Aisin:

     The Aisin Seiki was introduced in 2007.5 in Cab & Chassis configured trucks sporting the 6.7L Cummins Powertrain. This was designed to be a direct competitor with the Allison product of the time, and to date has only ever been used in 3500 and above trucks. In 2013, the AS69RC became an option in standard bed trucks contingent that they were 3500’s and sustained other associated frame and differential qualifications.

     There are two Aisin Seiki transmissions in the Dodge Diesel Truck lineup, but they are extremely similar. Hence, I will combine them into one common analysis with notes to identify the unique factors of each. They can be easily differentiated from the 68RFE based on the location of the transmission oil dipstick. Aisin Seiki equipped trucks will have the transmission oil dipstick on the driver’s side of the engine bay, as opposed to the 68RFE. 

     A simple way to understand the relationship between the elder AS68RC (used from model years 2007.5 to 2012) and the latter AS69RC (used from 2013 to present) is to think of the AS69RC as an evolved, strengthened and updated version of the horrendous AS68RC.

     The AS68RC was originally known for having miasmic pump and valve body failures that left the core totally unsalvageable. Fortunately, we created our “Formula One” AS68RC Pump and Valve Body to resolve this concern. The AS69RC does not suffer from these ailments, but shares the same common failure points.

*Bonus Knowledge* - The Aisin Seiki is actually owned by Toyota; much how Allison has a corporate relationship with General Motors. These are run-offs of the transmissions used in the Toyota Land Cruiser dating back to the mid-80’s.

Pros of the Aisin:

     Some may argue that it would be a short list, but the Aisin Seiki actually has a few notable points in the “plus” category. The AS68RC and AS69RC both require a substantial fuel de-rate to take place in order to change gears. A fuel de-rate is when the motor minimizes fuel delivery to alleviate some of the torque load on the transmission or other drivetrain components.

     The reason the factory has determined to do this in the Aisin Seiki is because if the AS68RC and AS69RC had to shift under full power, they would function but simply suffer from horrible longevity. This is because the transmission inherently cannot handle the torque of the 6.7L Cummins, and implementing this fuel de-rate allows us to mask this ailment through fuel delivery; a very low quality solution.

     As a result of this system, the clutches only apply under virtually zero torque load, yielding massive longevity in low stress applications. These are usually the success stories you hear about with 300,000 miles on one transmission; the guy who never used it outside of it's designed purpose. Unfortunately, it’s designed purpose is a little boring. Hence, this can become a large obstacle.

Cons of the Aisin:

     Let’s make one point clear, the AS68RC (whose High Pressure Oil Pump is pictured above) is undeniably the more problematic of the two Aisin Seiki transmissions. This is a testament to just how “out of place” this Toyota dinosaur was in the 6.7L Cummins. However, they both suffer from the same Achilles’ Heels in large part.

     The K2 hub, pictured below, strips itself alive inside the transmission. It must be made of billet to survive in any application, to include towing. This is a part that does not need added power to fail! Tasks as mundane as towing a gooseneck, or operating a welding rig are ample to destroy this critical internal component.

     It is due to this that the AS68RC and AS69RC both have deep limitations with power AND heavy towing for long periods of time. It is very rare we find this critical hub even serviceable during the rebuild process, making all Aisin Seiki’s found in the Dodge/Nissan Cummins an unobjectionable candidate for a quality, long lasting built transmission.

*Bonus Knowledge* - The Aisin Seiki found in the Nissan Titan appears to have a lower failure rate. We studied this and discovered that the Titan has a substantially lower Torque Multiplication Factor across the board, favoring transmission life slightly better than the overweight Dodge Ram diesel trucks.

     Further yet, it has the same problem that it does solution; the aggressive fuel de-rate. This fuel de-rate deprives this transmission of the ability to truly displace power efficiently. An Aisin Seiki truck will never be the fastest at the track if all other variables are equivalent.

     Lastly on this note, the transmission cannot be tuned. It’s electronic systems and encryption are too complex for current technological assets to encode modifications to the transmission’s control systems, rendering it effectively “untunable.” This is a huge “minus” compared to the highly versatile 68RFE.

     However, it should be noted that the Aisin Seiki units can be staunch and trustworthy transmissions without tuning. Simply put, it presents challenges that the 68RFE simply would not face due to its more advanced electronic aftermarket support. In fact, all of our AS68RC and AS69RC Transmissions are designed to comply with factory TCM configuration.

Can I perform a conversion from 68RFE to Aisin or from Aisin to 68RFE?

     The short answer? No. The long answer? You don’t have to and nor would you want to. The problems that arise the moment you want to switch from one heavily electronic transmission to another are deep, substantial and complicated. Not only is the hardware different, the entire brain of the transmission is simply different; every step of the way. There is no reasonable way to convert between any of these transmissions without presenting massive electronic challenges that do not have present solutions.

     An analogy that might bring more sense to this is as follows. If you have a PlayStation, and you try to play a video game that was designed for an Xbox, it will not be able to communicate with the PlayStation in order to work. Alternatively, a PlayStation 5 game would not work in a PlayStation 2, it’s just simply too new. Imagine this would be the relationship between the Aisin and the 68RFE, their entire electronic infrastructure is just simply different.

     In addition, the more successful AS69RC cannot be retrofitted to the 2007.5 to 2012 trucks either due to it’s electronic advancement. Fortunately, all 3 of these platforms are no stranger to us. We do proudly offer extensive solutions for all three, even the “Unicorn” known as the AS68RC.

The Conclusive Answer:

     The simple answer is this, regardless of which transmission your truck has, your best option is to replace or upgrade the transmission that it was natively manufactured with. This is the most comfortable and reliable way for any 6.7L Cummins to live. If your truck was made with an AS68RC for example, your best bet would be a built transmission such as our popular “Street AS68RC” and accepting whatever power limitations that may present, rather than attempting to convert to something else that the truck was never meant to accommodate.

     However, if you are an uncommitted buyer seeking information on which transmission to buy in your next new or used diesel truck purchase, avoid the AS68RC. It is just too problematic to justify. As for the 68RFE and AS69RC, they’re both great platforms that will undeniably need reworked completely to succeed when power is added or you intend to keep the vehicle for the long term.

     Regardless of which you have or proceed to have one day, Next Gen would love to be part of your project. If you need more information, or have questions on the best direction for your transmission build, give us a call today!