8F57 Introduction and Notable Features

This automatic transmission is an 8-speed transmission with electronic shift control and has a 4-element torque converter design, which includes a TCC. It has eight forward speeds, one reverse speed, four planetary gear sets, one Electric-Selectable-One-Way Clutch (more on this later), five friction clutches, and a main control valve body with eight solenoids. It also has an offset chain-driven pump to save space. The hydraulic control system of this transmission uses eight electronically controlled solenoids for:

• Shift feel (through line pressure control and shift pressure control; see the solenoid apply chart in figure one)
• Shift scheduling and timing (see clutch apply chart figure two)
• TCC operation

Before we get into the transmission, it’s good to know what the factory has specified for road testing the vehicle. So many times, we perform rebuilds on our customer’s cars, and they come back asking us why the car works the way it does. The customer may have been driving the car for some time, with the unit not shifting correctly. When they get the car working how it’s supposed to, they feel like something is not working right. Thank goodness we have guidelines from the factory (figure 3).

Upshift Sequence

At times the 8-speed transmission may skip gears when the vehicle starts from a complete stop. This is normal and a desired behavior.

At part throttle, when acceleration is brisk, single-step upshifts would result in very frequent shift events (a very short time in gear). Double-step upshifts result when a longer time is spent in gear.

However, at light pedal or road load, single-step upshifts will occur. This is because the small 8-speed gear steps allow the engine speed to drop to lower values than it would in the 6-speed transmission, providing the best fuel economy. In contrast, when the 8-speed transmission is at heavy or max pedal, the small steps keep the engine closer to the horsepower peak for best performance.

Downshift Sequence

At times the 8-speed transmission may skip gears when the vehicle downshifts to a complete stop. This is a normal and desired behavior. The same skip-shift strategy used for the upshift may be applied during a downshift.

Most performance-based automatic transmission DTCs require the fault to be detected consecutively multiple times (up to 5 times) before setting a DTC. Performing the shift point road test, as detailed below, increases the likelihood that a DTC sets if a fault is present in the system.

Shift Point Road Test

1. Bring the engine and transmission up to normal operating temperature.
2. Operate the vehicle with the selector lever in the D position.
3. From a stop, accelerate the vehicle to 80 km/h (50 mph), with the shifts occurring at approximately 2,000 rpm. Stay in 8th gear for 30 seconds or until the TCC applies. Repeat this two times.
4. From a stop, accelerate the vehicle to 80 km/h (50 mph), with the shifts occurring at approximately 3,000 rpm. Stay in 8th gear for 30 seconds or until the TCC applies. Repeat this two times.

Internally Speaking

The first notable feature is the small “squished” torque converter (figure 4). This thing is small! And if you think about it, it makes perfect sense. The torque converter part of the torque converter only functions for a short time. That is on take-off and hard acceleration. After the take-off happens, the torque converter clutch will come on very quickly. Let’s face it, the actual job of the torque converter to “convert torque” is not a very fuel-efficient operation. That said, most manufacturers are bringing the converter clutch on as soon as possible.

The next notable feature is the “Selectable One-Way Clutch” (SOWC) (figure 5). We have seen these recently in the 8F35 and the GM 9T50 transmissions. The previous SOWCs are controlled by a solenoid that sends oil to a valve, and the valve moves a plate that causes the SOWC to lock in both directions. The 8F57 SOWC has the solenoid attached directly to the body of the SOWC (figure 6). The solenoid pushes on a locking pawl to keep the SOWC from rotating in the free-wheeling direction (figure 7). Also, in figure 7, we can see the intermediate speed sensor and the locking pawl in the locked position.

Most, if not all, of the vehicles coming out these days, have an auto/ start/stop system built into the vehicle. The system is designed, so the engine shuts down at a signal or other stop event to increase fuel mileage. These systems have either a pressure accumulator or an auxiliary pump to keep the transmission pressurized so there is no time lag when the engine starts back up and the driver releases the brake pedal and steps on the gas. The transmission is already in gear, and off you go. The transmission fluid auxiliary pump does not have sufficient flow to apply the clutches but can keep clutches on when the engine stops and the main hydraulic pump stops providing pressure.

The majority of the auxiliary pumps produced today are typically bolted externally to the transmission case (think 9T50 or even the later model 6R80). The notable feature here is that the auxiliary pump is built inside the transmission case (figure 8).

Smart Pump

Not only is it a built-in pump, but it is also a smart pump. The electric transmission fluid pump has an internal microprocessor (figure 9). It communicates with the PCM over a PWM circuit with a frequency of 150 Hz with a duty cycle range of 10% to 90%. Because it has its own microprocessor, it also has its own set of trouble codes (figure 10).

If the transmission fluid level is low or overfilled or there are any restrictions in the transmission lines, hoses (if the vehicle is equipped with external lines or hoses), or cooler, it may affect the transmission fluid pump operation.

Fluid Level Check

1. Connect the diagnostic scan tool to the vehicle. Monitor the TFT PID.
2. With the engine running in PARK on a level surface, ensure the transmission is at the normal operating temperature of 85-93° C (185-200° F). If necessary, drive the vehicle until the transmission is at a normal operating temperature of 85-93° C (185-200° F).
3. With the vehicle in NEUTRAL, position it on a hoist.
4. Remove the fluid check plug (figure 11).
5. The fluid just drips out of the plug. If the fluid level is low, add Mercon®ULV ATF into the breather hole until it just runs out of the hole (figure 12).

The 8F57, Ford’s latest 8-speed offering, should be coming out of warranty any day now. Now that you have been introduced, you will be ready to service this vehicle when it shows up in your driveway. Always remember when you’re ready for what comes in the more you will have Fun with Transmissions.