Common GM 8-Speed Transmission Issues Reported by Owners

Overview of the GM 8L Transmission Family

The General Motors 8L family of transmissions has been a significant part of the company's lineup since 2014. These transmissions were introduced to replace older 6L six-speed units across various models, offering improved performance and efficiency. The larger 8L90 was the first in this series and made its debut in the 2015 Chevrolet Corvette C7 Stingray. Shortly after, the smaller 8L45 was introduced in the 2016 Cadillac CT6. Over time, the 8L family expanded to include many other GM vehicles.

The 8L90 is designed for heavy-duty use, capable of handling higher torque levels. It is commonly found in models such as the Chevy Silverado, GMC Sierra, and the Corvette. In contrast, the 8L45 is more lightweight and efficient, making it suitable for vehicles like the Cadillac CT6, Chevy Colorado, or the GMC Canyon. Despite being widely adopted and technologically advanced, the 8L transmission family has faced several issues that have raised concerns among owners and mechanics alike.

Common Problems with the GM 8L Transmission

Owners have reported a variety of problems with the GM 8L transmission, including noticeable jerkiness, gear slippage, hesitation, and shuddering. These issues are similar to those experienced by the later Chevrolet 10-speed transmission. As a result, the 8L family has become a frequent topic in technical service bulletins (TSBs) and owner forums.

According to AutoBlog, 39 owners from 26 different states filed a class-action lawsuit against GM, claiming that up to 800,000 vehicles equipped with the 8-speed automatic transmission experience hesitation, significant shakes, shuddering, jerking, clunking, or hard shifts. If these issues led to an official recall, it could be one of the largest transmission recalls in recent history.

Technical Issues and Design Flaws

Next Gen Drivetrain described the torque converter within the GM 8L as "uniquely untrustworthy" due to the poor functionality of the clutch design. The lock-up clutch assembly in front of the converter isn't designed for anything more spirited than normal driving. This can lead to long-term issues and accelerated wear and tear when towing, hauling, or accelerating aggressively.

Another common problem reported by owners is transmission fluid breakdown, which can cause the transmission to shudder, clunk, or shift harshly. Road and Track also reported that the same lawsuit recognized valve body design defects, which can cause the vehicle to shake or shudder at higher speeds.

Solutions and Technical Service Bulletins

In August 2019, GM introduced the 18-NA-355 technical service bulletin to address the torque converter problems. The TSB recommends a full flush of the torque converter fluid using Mobil 1 LV ATF HP fluid, which is specifically designed to handle this issue. Later, in January 2023, GM introduced the 20-NA-142 TSB, aiming to resolve the shuddering via a complete torque converter replacement.

GM also addressed the valve body problem with the PIP5437A TSB from November 2016, which recommends a transmission teardown and repair if debris is found. If no debris is present and the issue persists, GM advises replacing the complete valve body.

Legal Developments and Future Outlook

Reuters reported that in June 2025, a federal appeals court decertified the nationwide class-action suit, citing too many differences in vehicle models, state laws, and customer experiences. This decision handed a symbolic victory to GM. However, in another related legal development, the U.S. District Court for the Eastern District of Michigan denied GM's motion to compel arbitration, allowing the plaintiff to proceed with litigation in court rather than private arbitration.

While it may be a narrow win for the plaintiff, it represents a meaningful opening for continued legal action against GM. The future of these issues remains uncertain, both in terms of public perception and legal proceedings. Only time will tell how these challenges and their solutions will evolve.