As we’ve covered several times in the past, General Motors is facing several lawsuits over alleged defects in its eight-speed automatic transmission, which has been known to exhibit various drivability issues, including, shaking, jerking, and hard shifts. Now, new information provides an important data point in the GM transmission kerfuffle.
Based on court documents seen by GM Authority, GM may have been aware of the issues associated with its 8-speed transmission as far back as September of 2014. The documents cite a number of technical service bulletins (TSB) and other GM communications about issues associated with the 8-speed transmissions in question. Coincidentally, September 2014 was roughly the time that GM launched the eight-speed gearbox.
Besides the pending class-action suits, a variety of issues associated with eight-speed GM transmission have been documented through complaints filed with the National Highway Traffic Safety Administration (NHTSA), thus demonstrating the widespread nature of the issues.
The gearboxes in question are the 8L90 and 8L45 eight-speed automatic transmissions installed in a wide variety of rear-drive-based GM vehicles spanning the Chevrolet, GMC, and Cadillac brands. Vehicles specifically impacted include:
- 2015-2019 Chevrolet Silverado
- 2017-2019 Chevrolet Colorado
- 2015-2019 Chevrolet Corvette
- 2016-2019 Chevrolet Camaro
- 2015-2017 Cadillac Escalade and Escalade ESV
- 2016-2019 Cadillac ATS and ATS-V
- 2016-2019 Cadillac CTS and CTS-V
- 2016-2019 Cadillac CT6
- 2015-2019 GMC Sierra
- 2015-2019 GMC Yukon and Yukon XL
- 2017-2019 GMC Canyon
More than a dozen technical service bulletins (TSBs) seeking to remedy the GM transmission issues have been issued thus far. In August, we reported on the new 18-NA-355 TSB, which apparently fixes the issue via a special type of Mobil 1 automatic transmission fluid.
Specifically, the 18-NA-355 TSB addresses “torque converter clutch (TCC) shudder conditions” for the 8L45 and 8L90 eight-speed automatic transmission, RPO codes M5N, M5T, M5U and M5X. The issues appear to stem from moisture in the transmission fluid. In fact, some GM Authority readers have written in to tell us that the transmission flush using the Mobil 1 blue fluid via the 18-NA-355 TSB fixed the issues they were previously experiencing.
However, if the fluid swap doesn’t fix the issue, the next step may be a replacement torque converter, as a vehicle’s existing torque converter could have become glazed.