Cadillac 8-Speed Transmission Introduced on CT6
Cadillac advances its legacy of technologically driven performance and luxury with the Hydra-Matic 8L45 paddle-shift 8-speed automatic transmission, which debuts with the all-new 2016 Cadillac CT6.
Matched with the next-generation 3.6L V-6, the 8L45 transmission is based on the same acclaimed General Motors-designed eight-speed automatic family introduced on the Corvette Stingray – with the higher-capacity 8L90 version paired with the CT6’s available 3.0L twin-turbo V-6 engine.
“The shift performance of the new 8L45 paddle-shift eight-speed automatic transmission complements the CT6’s new threshold for efficient luxury to help take it to an even higher level,” said Bill Goodrich, assistant chief engineer for eight-speed automatic transmissions. “The shifts are quick and nearly imperceptible, establishing a benchmark for Cadillac.”
The 8L45 eight-speed shares the architecture and design features of the Hydra-Matic 8L90 transmission, but it is scaled and calibrated for the performance envelope of the new 3.6L V-6. It also incorporates components to support the engine’s stop/start technology.
Stop/start shuts down the engine to reduce fuel consumption when vehicle comes to a complete stop, and it automatically restarts the engine when the driver takes his or her foot off the brake pedal.
In addition to stop/start efficiency, the 8L45 eight-speed’s wide 7.0 overall ratio and numerically lower top gear offer an up to a GM estimated 5 percent fuel economy benefit over a comparable six-speed automatic transmission.
A numerically higher 4.62 first gear ratio also helps drivers start off more confidently, with a greater feeling of immediate performance.
“The 8L45 was designed to enhance the CT6’s driving experience, offering a strong balance between performance and efficiency,” said Goodrich. “Perhaps its best attribute will be that customers really won’t notice it – they’ll simply enjoy the CT6’s seamless, smooth driving experience and on-demand performance.”
Compact, mass-efficient design
With four simple gearsets for optimal efficiency and five clutches (two brake clutches and three rotating clutches), creative packaging enables GM’s eight-speed automatic to fit the same space as the previous six-speed automatic, with a lower weight.
The new 8L45’s smaller package size enables approximately 33 pounds (15 kg) mass saving compared to the 8L90 eight-speed – a transmission that was already lighter than GM’s 6L80 six-speed automatic.
Smaller steps between gears, compared to a six-speed transmission, keep the engine within its optimal rpm range, making the most of its horsepower and torque to optimize performance and efficiency.
Ratios compared: Hydra-Matic 8L45 vs. 8L90
| Type: | 8L45 eight-speed automatic | 8L90 eight-speed automatic |
| Gear ratios (:1) | ||
| First: | 4.62 | 4.56 |
| Second: | 3.04 | 2.97 |
| Third: | 2.07 | 2.08 |
| Fourth: | 1.66 | 1.69 |
| Fifth: | 1.26 | 1.27 |
| Sixth: | 1.00 | 1.00 |
| Seventh: | 0.85 | 0.85 |
| Eighth: | 0.66 | 0.65 |
| Reverse: | 3.93 | 3.82 |
Additionally, friction-reducing design features – including synthetic fluid – and lower spin losses via a powerflow that uses only two open clutches per gear and an off-axis binary vane pump contribute further to efficiency.
The torque converter design with turbine damper enhances refinement, particularly during low-speed gear changes, for smoother performance.
Architectural features
More than 1,100 computer-aided engineering analyses were made during the development of the Hydra-Matic eight-speed transmission family – resulting in more than two dozen patents – to ensure strength, durability, performance and refinement.
Architectural highlights include:
- A one-piece case with an integral bell housing for enhanced powertrain stiffness
- The grounding clutches are located rearward of the middle of the structure, outside the gearsets, and are splined to the case, eliminating the need for a the center support, which reduces weight
- The rotating clutches are located near the front of the transmission, with short oil feed channels, to support very fast shifts
- A unique oil-storage accumulator is incorporated to support stop/start technology. It ensures the clutches have oil for immediate take-off when the engine is re-started
- World-class shift time quickness and responsiveness are accomplished with a Gen II controls system, which works with variable force solenoid technology and three internal Hall Effect speed sensors
- The transmission controller is mounted externally and its processor executes hundreds of calculations and commands every 6.25 milliseconds.
The Hydra-Matic 8L45 and 8L90 transmissions are built at GM’s Toledo, Ohio, and Silao, Mexico, transmission facilities. They will also be offered in the 2016 Cadillac CTS and ATS, including CTS-V and ATS-V.
| 8L45 eight-speed automatic | 8L90 eight-speed automatic | |
| 2016 CT6 | 2.0L Turbo I-4 and 3.6L V-6 | 3.0L Twin Turbo V-6 |
| 2016 CTS & CTS-V | 2.0L Turbo I-4 and 3.6L V-6 | 6.2L Supercharged V-8 |
| 2016 ATS & ATS-V | 2.5L, 2.0L Turbo I-4 and 3.6L V-6 | 3.6L Twin Turbo V-6 |
Content and images provided by: General Motors
