Aisin Seiki AS66RC Transmission • Problems & Solutions

Aisin Seiki AS66RC Transmission • Problems & Solutions

Nathaniel ValentinApril 15, 2024

Table of Contents:

- Introduction to the AS66RC Transmission
- Aisin Seiki AS66RC Product Resources
- Popular Transmission Information Resources
- In this Drivetrain 101, we will be addressing
- A Brief History of the AS66RC Transmission
- How the AS66RC clutch packs work
- Problem #1 - The Torque Converter
- Problem #2 - The High Pressure Oil Pump
- Problem #3 - The Valve Body
- Problem #4 - The K1 Clutch Assembly
- Problem #5 - The K2 Clutch Assembly
- Problem #6 - The K3 Clutch Assembly
- Problem #7 - The Internal Wiring Harness
- Problem #8 - The OEM Solenoids
- Problem #9 - The OEM Bushings
- Conclusion to the AS66RC Transmission

Introduction to the AS66RC Transmission:

     As the inventors of the famous Project Carbon AS69RC High Pressure Valve Body Upgrade Kit, we at Next Gen Drivetrain are proud to be at the forefront of the AS69RC market. If you own a Ram or Nissan truck featuring the infamous AS69RC, you likely know Next Gen Drivetrain as the best place for uparmored AS69RC transmissions and parts, designing unique parts and building them for a diverse spectrum of applications. All too often, we are approached with question after question about this highly complicated transmission; ranging from what fails to why and how. Fortunately, we've fulfilled this demand with an installment in our popular Drivetrain 101 series.

Aisin Seiki AS66RC Product Resources:

- AS66RC Transmissions
- AS66RC Torque Converters
- AS66RC Rebuild Kits
- AS66RC Valve Bodies
- AS66RC Parts

Popular Transmission Information Resources:

Top 5 Benefits of an Upgraded or Built Transmission
Calculating Torque Multiplication Factor, Why is it So Important?
- Top 5 Ways to Extend the Life of a Factory Transmission

In this Drivetrain 101, we will be addressing:

- The most popular failures we witness on the AS66RC transmission

- Its capabilities (or lack there of) in reference to TCM tuning and shift/lockup protocol modification

- The strengths (believe it or not, there are a few!) of this transmission

- Footnotes for Ram AND Nissan owners

And much, much more!

>>> View our AS66RC Transmissions & Parts Catalog Here!

A Brief History of the AS66RC Transmission:

 The AS66RC transmission is used in both Nissan Titan pickup trucks and Ram Heavy Duty pickup trucks. Nissan, uses this transmission in all gas powered pickup trucks of the current generation, whereas Ram selectively uses this unit only in the heaviest duty applications. 

     After much trouble utilizing the 66RFE in heavier duty Ram trucks powered by the gasoline motor, it eventually became evident that something different was necessary to support the ferocity of the 6.4L Hemi motor along with the Ram 3500 through 5500 platform. In 2013, Mopar transgressed to using Aisin Seiki transmissions in these intense applications.

     The diesel powered vehicles received an AS69RC transmission, whereas the gasoline powered vehicles with less torque used the AS66RC transmission. This unit, essentially a Toyota SUV transmission repurposed, has come with mixed reviews. The AS66RC transmission is still in production today.



How the AS66RC clutch packs work:

     The AS66RC transmission is 100% TCM controlled. Due to it’s incredibly complex security encryption, the TCM protocol is almost impossible to modify. This is why you see no TCM tuning in the Aisin Seiki community.

     Fortunately, the AS66RC factory shift and lockup protocol is quite favorable and all improvements to it’s drivability and behavior are to be made inside the units mechanisms rather than through TCM Tuning. 

    To recognize some basic operating facts about this transmission, the Aisin Seiki AS66RC transmission is a 6 Speed Automatic computer controlled transmission, with lockup capable torque converter. In the drive position you will have 6 forward speeds.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     When pressing the “tow haul” switch or “O/D off” switch on the end of the shifter handle once you will omit 6th gear and have later upshifts into all other gears. Press the switch a 2nd time and you will omit both 5th and 6th gears. Pressing 3rd time will give you full upshifts of all 6 gears again.

     Below, you will see a comparison of the AS66RC transmission final drive ratios as compared to other transmissions used across the same period of time. You can see that the AS66RC transmission final drive ratios are almost identical to that of the AS68RC.

      These shifts, like most 6 speed transmissions, are controlled purely by the energization and de-energization of an array of pressure solenoids about the valve body. This unit also uses one singular pressure switch. Below, you can see the how solenoid application correlates to the activation of each gear within the transmission.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     As you can see, the AS66RC transmission is immensely complex. No attempt was made to simplify this transmission, especially electronically. The end result was a transmission that has tremendous operational capabilities, but simply suffers from it's own inherent complexity. Fortunately, Next Gen welcomes highly complicated drivetrain challenges. Now, we will observe the most prolific failure points in the Aisin Seiki AS66RC Transmission and how we permanently resolve them!

Problem #1 - The Torque Converter

     Much like the former AS68RC, the AS66RC transmission uses a 3 steel/3 friction lockup assembly from the OEM. This allows for above average torque capacity, despite their small size. Unfortunately, the 3 disks are so small that the torque capacity is roughly the same as a 68RFE torque converter.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     In fact, it has LESS friction area than the 66RFE transmission torque converter clutch, but the massive line pressure capabilities of the AS66RC transmission compensates for this just slightly. We have not found an accurate way to measure this to provide further data, but this much we can confirm.

     Further, the converter cover can be aggressively eaten up by the steels synchronizing against the friction elements of the converter clutch at rapid speeds, contributing to converter cover failure. The cover is the component on the front side of the converter that bolts to the flexplate.

     There beyond, the stator assembly (the component that controls stall speed) is made of cast aluminum and doesn’t “break” but does suffer from other issues. It is grossly inefficient, robbing the truck of a considerable amount of power.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     Clients who purchase only a torque converter report massive differences in drivability and perceived power for this reason. It should be noted that this modification does not “add” power, but does restore lost power in lower gears where the TCC is not engaged and the stator is largely responsible for how much power reaches the ground.

     Luckily, our AS66RC torque converters all come with an upgraded torque converter clutch assembly, stator, impeller hub, piston and more. We offer full-billet options for more audacious applications, but it is important to have this basic host of modifications in your AS66RC to support virtually any goals. This is because power is not the only thing that breaks this transmission.

Problem #2 - The High Pressure Oil Pump

     Much like the preceding AS68RC transmission, the pump is one of the most common failure points in this transmission. It’s poor longevity is attributed to its basic design, a single stage dual-gear pressure pump. It functions largely the same as an LS motor oil pump, pressing the pump gears against one side of the pump at all times.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     Over time, the gears will attempt to “push” to the side opposing the oil galley that feeds the valve body. When this happens, the pump gear galley will become oblong in shape, beginning to resemble an egg. When this happens, two things are effected.

     One is the ramp rate of oil pressure being produced due to its lack of vacuum inside the pump assembly. The other is a lack of peak pressure, again for the same reason. Customers whose pumps are beginning to wear often report less concise shift quality than date of purchase, or “wonky” shift behavior.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     A proper oil pump consists of coated pump gears that do not pierce the surface of the pump’s metal, negating this longevity-inhibiting problem. It is for this that any pump that arrives here unserviceable is replaced with a new OEM before the remanufacturing and upgrading process begins.

Problem #3 - The Valve Body

     One should be able to start seeing a trend that this transmission suffers from most of the same failure points as it’s predecessor, and hence one could logically see how the valve body is also a tremendous failure point. Fortunately, the AS66RC valve body is modular in design and easy to replace.

     Unfortunately, AS66RC valve bodies are designed to be proactive upgrades, not reactive repairs. If you’re experiencing codes or ill behavior of the AS66RC, a valve body may have been the route cause, but will not fix the problem. This is because valve body issues almost all produce a lack of oil pressure.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     To further complicate things, this symptom often only becomes detectable by the driver once it damages the clutch elements inside the transmission beyond their ability to properly engage, causing the symptoms many people report. In fact, much of the AS66RC transmissions poor drivability comes from the OEM accumulator and dampener set inside the valve body.

     From the OEM, this transmission comes with 5 main accumulators and one main dampener. There are tiny secondary accumulators that are seldom problematic. At Next Gen, we have invented the only full billet accumulator and dampener set available, featuring 2 O-Rings per piston as opposed to the factory zero. Further, they come with an entirely recalibrated accumulator spring set.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     This allows us to say we have the only air-tight AS66RC accumulator set in existence, yielding crisp, welcoming and concise shifts. This is a must for everything from stock trucks looking for preventative measures all the way to highly technical performance applications.

     It is for this that our coveted Project Carbon™ AS66RC Valve Body Upgrade Kit is standard in all valve bodies, rebuild kits and transmissions we offer for the AS66RC transmission community. You can learn more about our 100% engineered and machined in-house Project Carbon™ AS66RC Valve Body Upgrade Kit here.

Problem #4 - The K1 Clutch Assembly

     K1 is known as the “underdrive” clutch assembly, being used in all underdriven gears. It features 7 low quality clutches that engage the moment the truck enters drive and uses a massive dampener in the valve body. As mentioned previously, we offer a billet dampener unlike anything in existence, but that only gets us so far.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     From the OEM, this clutch pack comes with a set of low quality stamped steels and a set of cheap papers designed for smooth engagement. In fact, the pattern of the clutches matches most heavy passenger vehicles such as a city bus. It is designed to synchronize slowly and be ultra-smooth.

     Ultra-smooth, although nice for many communities, is not nice for the Ram and Nissan AS66RC community because it lacks the confidence necessary to capacítate added power or heavy towing. The goal here is not “aggressive” shifts, but rather simply refined shifts that are a bit crisper than the OEM.

     Because of this, we see many K1 failures associated with higher mileage, deleted trucks and frequent towing. Our most basic complete transmissions will still offer a higher quality clutch material in this portion of the unit as well as our popular laser cut and hand finished steels. 

>>> View our AS66RC Transmissions & Parts Catalog Here!

     An upgrade in clutch material and steel quality can yield as much as 25% more torque capacity without increasing the capacity of the assembly, a massive gain. However, we can always increase the quantity of friction elements inside this drum for ultra-high power applications. This is standard in units such as our Formula One AS66RC Transmission.

Problem #5 - The K2 Clutch Assembly

     More problematic than K1 is K2, also known as the “overdrive” clutch assembly. This system is engaged during the 3-4 upshift and stays engaged in all forward gears above that, making it critical for gears 4, 5 and 6. As in all transmissions, the upper gears have the highest Torque Multiplication Factor, causing them to often be the first to fail; especially with a measly 6 low quality frictions.

     Beyond even this, the hub that these clutches spline onto is made of flexible and thin stamped steel; quite scary for most applications. Every time the transmission enters 4th gear, this hub is forced to synchronize in speed with the input shaft. The more weight the truck is carrying behind it, or on it, the more stress this component experiences.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     For these facts together, almost every application can justify a Billet K2 Hub assembly. However, that is not all that’s necessary. A billet piston and backing plate are necessary to adjust the capacity of this drum, and upgraded clutch materials and steels are critical for success.

     Unfortunately, the OEM does not see it this way, offering an overdrive assembly almost congruent with the Toyota Land Cruisers of decades past. It works for most things, so it should work for a large truck, right? Wrong.

Problem #6 - The K3 Clutch Assembly

     Less frequently damaged, but still worth discussing, is the K3 clutch assembly and drum. These clutches are used in third and fifth gear, giving them a slight break from the aggressive 4-5-6 clutch pattern of K2. For this, we usually see failures of K3 drum associated with sizable power increases in excess of 700HP.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     But, just because you are under 700HP doesn’t mean you’re safe. Perhaps flexion and cracking of the drum is not so probable at low power, but incinerating the factory paper on the OE clutches is. This is because the unit does not offer a high capacity of clutches in this part of the transmission and just rely on the same 6 frictions used in K2. 

     Because of the AS66RC’s factory use of a cheaper high energy material, a material favoring smooth engagement over durability, the minimum to capacitate even a stock truck for any extended period of time consistently is an upgraded clutch and steel material.

     Logically, we prefer a heavy duty organic friction and our standard laser cut steels as a bare minimum. For more audacious applications, we convert to a high capacity steel drum assembly to dramatically increase overall torque capacity.

>>> View our AS66RC Transmissions & Parts Catalog Here!

Problem #7 - The Internal Wiring Harness

     This is a rather simple problem, a welcomed change to the usual. The OEM internal wiring harness is oriented in a very complex and convoluted shape that makes internal cracking of wires a very very high risk. It’s much like bending a paper clip back and forth until it simply snaps.

     The OEM later updated this with a new OEM wiring harness offering slightly thicker gauge wiring inside that negates this concern and is far more befitting the application. As always, Next Gen has a solution. We are the only transmission company direct with Aisin Seiki corporate, allowing us to offer these updated products far faster and more accessibly than the dealership who simply waits for Mopar or Nissan corporate to use their current supply before carrying updated part numbers.

>>> View our AS66RC Transmissions & Parts Catalog Here!

Problem #8 - The OEM Solenoids

     OEM solenoids are usually the most reliable option for any rebuild, and frankly, the Aisin Seiki lineage is no different. That being said, why are solenoid codes such a popular problem on this transmission? Let’s learn something.

     We have said over and over again for years that the AS66RC transmission, despite its many issues, is not a “dumb” transmission. In fact, the TCM protocol of this unit is among the most complicated from its generation and even rivals current 8 and 10 speeds in complexity.

     Hence, both Nissan and Ram will often throw codes when a pressure solenoid is pushed on by oil pressure at the wrong time or does not turn on when the TCM energized it with control voltage, expecting it to turn on.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     This generally happens not because of the solenoids, but because of internal oil crossleakage of the valve body forcing solenoids open when they should be closed and otherwise. When this happens, the truck does not understand the problem but does understand the solenoid is acting irrationally.

     As a result, the truck will throw a solenoid code denoting voltage being high or low, or a more generic “Friction Element Apply” fault code. Generally when these codes present, the solenoid is suffering from the valve body doing what it wants to do rather than the solenoid itself being an inferior design.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     This is why OEM solenoids last incredibly long (sometimes upwards of 500,000 miles!) so long as the transmission stays otherwise together. This further explains why we witness an extraordinarily low and virtually nonexistent failure rate of OEM solenoids on our built transmissions as well as our Formula One AS66RC Valve Body, but yet it appears so common on factory transmissions.

Problem #9 - The OEM Bushings

     Much like many transmissions on the road, the Aisin Seiki lineage uses a low quality babbitt material to manufacture bushings. The concern here is that babbitt bushings in any transmission usually have a 150,000 to 200,000 mile terminal life span. 

     This does not mean that the transmission cannot exceed these miles under very fortunate and unlikely conditions, but what it does mean is that there is a noticeable drop-off in smoothness during this time frame. Most units will experience issues before this that have been paired to deleted or tuned trucks, as well as those with intense applications.

>>> View our AS66RC Transmissions & Parts Catalog Here!

     A more quality solution would be bronze bushings, a standard on nearly all Next Gen transmissions. The intent is to produce far greater longevity as bronze bushings have no determinate life span.

     Although they feel the same as babbitt bushings on day one, they will feel new at virtually any mileage while babbitt bushings quickly begin to degrade and are noticeably less confident as mileage increases.

Conclusion to the AS66RC Transmission:

     If you own an AS66RC transmission, do not fret. This transmission has the capacity for excellent longevity, frankly in excess of almost any other direct competitor. They also capacitate massive power levels once appropriately built for the application. They may be an underdog from the factory, but can be easily upgraded to endorse crisp shifts, cool operating temperatures, incredible reliability and low cost of lifetime maintenance. Still have questions? Call in and speak to one of our experts today!

>>> View our AS66RC Transmissions & Parts Catalog Here!

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