Other Articles - June - 2021

A Look at the Corvette Tremec TR9080

Get in, buckle up and hold on is what a friend told me as we went for a drive in his 2021 Corvette. Zora Arkus-Duntov, the father of the Corvette, made a statement at the end of the 12 hours of Sebring in 1957 that the engine needed to be moved to a position behind the driver. Sixty plus years later, GM introduced the 2020 mid-engine Corvette.

Chief engineer on the C8 Corvette, Tadge Juechter, wanted a car that would get 30 mpg, go 0 to 60 in 3 seconds, offer driving comfort for the operator and passenger and be base-priced around the 60K range. To accomplish those goals, they equipped the vehicle with a 6.2L small-block V8 (RPO LT2) and an 8-speed DCT transmission (RPO M1L) (Figure 1).

The TR9080 DCT is supplied to GM from Tremec, a many decades-long manual transmission supplier to GM, Ford, and Chrysler. The TR9080 is the cousin of the TR9070 used in the Ford Shelby Mustang. The TR9080 is an 8-speed wet-clutch DCT equipped with either a mechanical limited-slip differential (mLSD) or an electronic limited-slip differential (eLSD).

Tremec produces both mechanical as well as mechatronic components. Tremec purchased Hoerbiger Drivetrain Mechatronics, a Belgium-based company that is a supplier for Mercedes, Ferrari, and McLaren DCT components.

Making up the TR9080 are five aluminum component housings used to support multiple shafts, five synchronizer assemblies and shift rods, two multiple disc clutches, and a bunch of gears and bearings.

The electronic control systems consist of multiple valve/solenoid bodies, as well as sensors to support the unit’s operation. Like other DCT transmissions, the TR9080 utilizes two input shafts, each connected to a clutch. One shaft and clutch are in charge of the even gears (2-4-6-8), while the other controls the odd gears (1-3-5-7) (Figure 2).

In addition, the flywheel is equipped with a pendulum dampener. It operates very similar to the pendulum dampener torque converter designs in use today, eliminating vibrations due to engine firing frequencies.

The fluid for the TR9080 is Pentosin FFL-4, a fully synthetic product produced by Fuchs and sold by AC Delco (Figure 3). The fluid change interval is 45,000 miles (72,000 km), while the filter is designed to be serviced at 7,500 miles (12,070 km), then at 22,500 miles (36,000 km), and at 22,500 miles (36,000 km) intervals from that point forward. Fluid capacity is based on vehicle use. Normal operational capacity is 11.6 qt (11L), but if the car is used for racing, capacity should be raised to 13.7 qt (13 L).

Like other DCT transmissions, the TR9080 stages the shifts and simply swaps clutches when changing from and odd to even or even to odd gear. For example, when operating in first gear, the transmission positions the shift system into second gear. To make the change to second gear, the system releases the odd clutch and applies the even clutch to provide power flow thru the unit.

On a forced downshift, the system can skip shifts. For example, if you are in 7th gear and you aggressively accelerate, the computer can shift the transmission from 7th to 4th, skipping 5th and 6th gear.

Many different inputs such as g-force and brake pressure are used to decide when the transmission should upshift and downshift so the transmission can do some things that may surprise you. As an example, if you are decelerating and braking hard into a turn, the transmission will downshift early as you enter the turn. If you are exiting the turn with a high g-force, the transmission will delay the upshift. The shifts are clean and crisp, with this transmission taking less than 100 ms to complete.

The shifter is a button style with P, R, N, D, and M ranges available. Manual shift control can be deactivated by lifting the D switch on the shifter panel. When in manual shift mode, the transmission will automatically downshift as you are coming to a stop. If you are in manual shift mode and you want to accelerate aggressively, you can pull and hold one of the shifter paddles. This will cause the transmission to downshift to the lowest gear possible for the speed you are driving. Pulling and holding both shifter paddles will cause the transmission to enter declutch mode (Some folks call this burnout mode). This mode releases both clutches and allows the engine to accelerate as you apply the accelerator pedal. Releasing the paddles reengages the clutch so the vehicle can aggressively accelerate.

VALVE BODIES

MAIN (MAV) valve body

The main valve body houses the following components:

  • Eight solenoids
  • Multiple valves; Clutch proportioning, Clutch RSV, eLSD proportioning, eLSD RSV, System pilot, Clutch cooling, Pressure regulator, Cooler bypass, Cooler pressure regulator, LP safety, HP safety
  • Three clutch pressure sensors (Odd clutch, Even clutch, eLSD)
  • One temperature sensor

SYNCHRO ACTIVATION (SAV) valve body

The synchro activation valve body houses six electro/mechanical actuator solenoids that are used to move the shift rails. In addition, a pressure sensor that measures line pressure is mounted on this valve body.

Located below the synchro activation valve body are two sensor modules, the odd sensor module, and the even sensor module. The sensor modules are used to provide feedback regarding each shift fork position through shift fork position sensors 1,2,3,4, and 5.

Valve Body Programing

Like the GM 8, 9, and 10-speed applications, if either the SAV or MAV valve bodies are replaced, the TCM must be programmed with the updated flow rate values for the new parts. The PUN (part unique number) is a 22 digit number that is located near the QR labels on the valve body. The programing software will request the new PUN numbers to load the correct software. One thing is confusing when it comes to programing this application. There is also a 21 digit number located on the parts, and if that number is used, the programming software will not function as it requires the 22 digit PUN.

PARK LOCK ASSEMBLY

The park lock assembly is used to control the parking pawl, which provides park position. The park lock assembly consists of:

  • A park lock solenoid actuator
  • A park lock stepper motor
  • A park lock solenoid
  • A park lock position sensor

SPEED SENSORS

The TR9080 uses three speed sensors, two input speed sensors, and an output speed sensor. The 43 toothed 4th gear generates the output speed sensor signal. The even gear input speed sensor monitors the rotation of the 29 toothed 2nd gear. The odd gear input speed sensor monitors the 41-tooth 3rd gear rotation. All of the sensors are two-wire hall-effect designs that are fed a 9-volt signal from the TCM and produce a 3.5-volt square wave output to the TCM based on rotational speed. The speed sensors are mounted in the sensor modules.

TCM

The TCM is a 32-bit stand-alone processor mounted behind in the passenger side rear tire wheel well area.

CLUTCHES

There are two clutch packs used to drive the two different input shafts. Both clutches are contained within the same housing. The odd gear outer clutch has five (5) friction plates, while the even gear inner clutch has six (6) friction plates. The clutches are fed from passages you would typically call the stator support as the clutch housing is mounted where the torque converter would normally be located.

FAST LEARN

Like other transmissions, the TR9080 has adaptive learning capabilities. The adapts need to be cleared, and a fast learn performed if any of the following occur:

  • Transmission replaced
  • Repairs performed that can affect shift time, such as clutch replacement
  • TCM replaced
  • TCM calibration was updated

The process requires the use of a quality scan tool and is very similar to other applications. On this application, the process is displayed on your scan tool, so it is as simple as following the steps displayed. Keep in mind, like other applications, you must achieve the correct transmission fluid temperature for the fast-learn process to function. (140-212 °F, 60-100 °C)

Well, that is about all the time we have for now. Until next time remember, “life is too short to drive boring cars.”