If you build cars, you have to follow certain federal regulations that dictate a minimum fuel economy standards for your vehicles. You can achieve these MPG numbers in many different ways. But one of the most common is to give to your vehicles tall gearing, then fit the transmission with lots of overdrive gears so the engine RPM can drop when you’re cruising to save fuel. That was the idea behind the GM 9T50 transmission: Create a GM 9 speed transmission that could provide enough gear ratios for good fuel economy, yet still shift fast enough to give smooth performance.
What Transmission Do I Have?
In order to fit three extra gears into the same space as a 6 cog unit, GM engineers had to get creative. To that end, they stacked all of the gears in line with the engine’s crankshaft. The allowed for a more compact design, and provided the inspiration for one of the most unique features of the GM 9T65 transmission; the selectable one way clutch.
In a typical GM 6 speed automatic (like the 6T70E), first and reverse gears have separate clutch packs, which take up a lot of space. The 9T65 one-way clutch however, utilizes a single clutch that can both lock in place or freewheel on demand. To do this, the designers essentially linked two narrow sprag clutches together, then fitted a controllable mechanism to one of the clutches that would keep the sprag elements collapsed to allow freewheeling when necessary. When the 9T50 transmission control unit commanded, the special mechanism would release the sprags to allow the clutch to lock up.
Since improving fuel economy is a multistep effort, it’s important to have a reliable stop/start system that can shut down the motor to save fuel when the vehicle is stationary. However, this requires that there be enough transmission fluid pressure to engage first gear when the driver wants to pull away. To achieve this, the 9T50 9 speed automatic has been fitted with a special coil spring accumulator that can hold fluid pressure when the motor shuts off. The 9T50 valve body has also been fitted with a special expansion tank, that allows the TCM to precisely control the fluid pressure as needed.
And speaking of the 9T50 transmission control module, it’s fitted with a special 32-bit processor that is mounted on the outside of the transmission case. The 9T50 TCM is also calibrated to compensate for normal clutch wear, and it’s programmed for manual control capability, along with automatic grade braking.
9T50 Transmission Problems
9T50 Shifting Problems
A common 9T50 transmission problem can occur during warm up and normal driving. If the transmission is cold, and pronounced deceleration can occur during the 1-2 upshift. This may also happen when the transmission being manually shifted from 1st to 2nd gear. When the transmission is warm, a momentary neutral may occur during the 2-4 upshift. The check engine light may also illuminate.
Cause – This issue can occur on early production 9T50 transmissions due to a undersized 9T50 spacer plate orifice between the 9T50 valve body and transmission case.
9T50 Transmission Specs
General – 9-speed automatic
Application – RWD / AWD
Production Began – 2018
What Transmission Do I Have?
9T50 Transmission Gear Ratios
First – 4.69
Second – 3.31
Third – 3.01
Fourth – 2.45
Fifth – 1.92
Sixth – 1.45
Seventh – 1.00
Eighth – 0.75
Ninth – 0.62
Reverse – 2.96
