Since the days of the A40 and A340 units, I had engraved this image of Toyota rear-wheel drive transmissions in my mind. From the long, rectangular oil pan with a valve body to match it to the sharp clutch splines in the case that always left me cut up, not much has changed with them through the A760 series units. Until now, the AC60 seems to have changed normal expectations and defined a new era. Though the exterior of the transmission is like its predecessors, the insides open up a whole new world. There are fewer parts. It almost seems like something is missing! Let’s explore what Toyota has done with a simplified version of rear-wheel drive transmission technology moving forward.
The AC60 transmission is a light to medium-duty unit. It comes in a standard and higher torque capacity application and two- and four-wheel drive. The AC60E designation is the two-wheel drive version, while the AC60F denotes the four-wheel drive unit. All versions of this unit use a three-piece design consisting of the main case, removable bell housing, and extension housing.
This transmission can be found in most small to mid-sized pick-ups that Toyota currently produces. They also extended the applications to include a minivan (the HiAce) prevalent outside of the US and the base trim V6 Land Cruiser (figure 1). The Tacoma is the most popular application to find in North America.
GEARTRAIN AND CLUTCHES
So, what’s so special about this transmission compared to other 6-speed rear-wheel drive units that Toyota has produced? I’m glad you asked! It’s almost like management told the engineering department to discard their previous ideas and start new ones. So, starting with the gear train and clutches, you will notice ‘less stuff’ inside.
The AC60 uses three planetaries, three brake clutches, two rotating clutches, and a mechanical one-way to produce six forward gears and one reverse range (figure 2). The A760 also uses three planetaries. In addition, it uses four brake clutches, four rotating clutches, and four one-way mechanical elements to produce the same result.
Keeping the A760 for comparison, a significant change is noted for the AC60 units. The A760 uses nine solenoids to the AC60s seven; four of which are full-flow designs (figure 3). The full-flow solenoids handle all the direct pressure for clutch application and release. When servicing these solenoids, return them to their original positions. Ensure that the screens are intact and the valve stroke completely and freely.
When bench testing full flow solenoids, perform a resistance test. SL1 through SL4, SLT, and SLU measure 5-5.5 ohms of resistance. You can use a 12-volt source to operate the solenoids for testing.
Toyota recommends a load limiter in the test circuit (figure 4). A 21-watt headlamp is sufficient to allow enough current flow and protect the solenoid coil from damage. Apply and release power to the solenoid and listen for a “click.” Also, observe the operation of the internal valve.
THE VALVE BODY
There are check valves in this valve body, but no check balls! Be very careful when separating the halves (figure 5). Most valves and springs are the same, apart from a few. The number of valves inside the valve body has been reduced compared to previous designs. The full flow solenoids and TCM strategy require fewer valves to control shift quality (figure 6).
The TCM programming uses transmission sensors and CAN bus data from other sensors and modules to control the line pressure, shift scheduling, shift feel, TCC scheduling, and TCC apply and release rates. The clutch application and release rates are directly controlled through the commands given to the SL1-4 solenoids. Since they are direct acting, precise control of applying and release rates are achieved using the input and output speed sensors as real-time feedback for clutch torque transfer rates. The computer can calculate how long a shift takes and adjust for the following shift sequence, preventing tie-ups and flares. In addition, optimal shift overlap times are achieved.
For the most part, this unit has proven reliable and durable; however, Toyota owners seem to complain about how the unit feels. Driving this vehicle in traffic does feel like it is laboring unnecessarily. The shift scheduling often places the vehicle in 4th gear and full lock-up by 30 mph. In the 2.7L Tacoma application, the vehicle feels as lively as a smooth jazz concert!
Selecting the ECT PWR button, which commands delayed shift scheduling, makes the vehicle feel livelier (figure 7).
The shift scheduling program seems to fall in line with fuel-saving strategies. Unfortunately, this is considered normal, and it’s good to be aware of this common trait, especially when making transmission-related repairs. Always check for the latest TCM programming updates and perform them.
It is beautiful to see a manufacturer produce something with greater simplicity in a world of increasing complexity. As a result, this unit has made its mark on the world market and will remain with us for some time. As the number of transmissions produced increases, so will the likelihood of us working on them. In the meantime, the information provided in this article gives you a jump on understanding and successfully repairing this unit so you can confidently deliver the goods to your customers!