Nine is quickly becoming the new six. After years of rule by the six-speed automatic transmission, nine-speed autos are beginning to gain footing, slowly replacing the six-speed as standard.
For General Motors, it tapped rival Ford to co-develop a new, in-house nine-speed automatic. It was engineered alongside the ten-speed automatic gearbox for rear-wheel drive vehicles, which Ford took the lead on, while GM focused on the nine-speed for front-wheel drive applications.
Motor Trend took a look into what’s actually inside GM’s latest transverse 9T50 transmission, and not surprisingly, it’s full of modern engineering.
According to GM transmission expert Scott Kline, the nine-speed gearbox’s goal was to use the same six-speed design, but add three additional cogs. Thus, it keeps its on-axis design, keeping the planetary gears aligned with the crankshaft.
To keep width and length down, GM and Ford completely redesigned the system responsible for shifting the reverse and first gears. Instead of the six speed’s old two-clutch system, a “selectable one-way clutch” was developed and stacked together.
This allows for the clutch to lock like a multiplate clutch resisting motion in both directions, ditching a conventional multiplate design.
To keep engine vibrations speeds at a minimum, a new torque converter is present, which allows for small bursts of 10-60 RPM speed differentials. It allows for smoother operation regarding the lock converter and greater efficiency altogether.
The nine-speed automatic also has been engineered for start-stop functions with transverse engines, meaning there’s a large oil-pressure accumulator to help the clutches in first gear while the engine restarts. As for maintenance, a second filter has been fitted to ensure debris do not enter the gearbox. The filters are reportedly sized to never need replacing.