Since their introduction in 2014, the General Motors 8L series of transmissions has been implemented across a broad spectrum of the company's vehicle lineup, eventually supplanting older 6L six-speed units. The high-torque 8L90 first appeared in the 2015 Chevrolet Corvette C7, while the more compact 8L45 was unveiled in the 2016 Cadillac CT6. Despite their advanced engineering and widespread deployment, these transmissions have faced significant scrutiny regarding their long-term reliability.

Reported Performance Issues

Owners frequently report specific operational difficulties with these units, mirroring complaints later seen in GM's 10-speed transmissions. Common grievances include:

  • Noticeable jerkiness during shifts
  • Gear slippage
  • Hesitation
  • Unwanted shuddering

According to experts at Next Gen Drivetrain, the torque converter design is particularly problematic, specifically citing the unreliable functionality of its clutch mechanism. This component was not engineered to withstand aggressive driving, meaning that heavy tasks such as towing or frequent hard acceleration can lead to premature wear. Furthermore, degradation of transmission fluid is a known contributor to harsh shifting and shuddering. Reports also indicate that flaws in the valve body design can lead to vehicle instability at higher velocities.

GM’s Technical Responses

In an effort to mitigate these widespread concerns, General Motors has issued several technical service bulletins (TSBs):

  • Torque Converter Fixes: In 2019, TSB 18-NA-355 recommended a complete flush of the torque converter fluid using a specially formulated Mobil 1 LV ATF HP fluid. By early 2023, TSB 20-NA-142 was introduced, suggesting a full replacement of the torque converter as a definitive solution for shuddering issues.
  • Valve Body Repairs: Addressing potential valve body defects, TSB PIP5437A from 2016 outlines a procedure involving a transmission teardown. If technicians discover debris, the system must be repaired; if the issue persists without clear debris, GM advises a total replacement of the valve body.

Legal Context

The transmission issues have led to significant legal challenges. In a notable development from June 2025, as noted by Reuters, a federal appeals court decertified a nationwide class-action lawsuit, noting the excessive variance in vehicle models, state regulations, and individual owner experiences. However, the legal battle is not over. In a separate proceeding in the U.S. District Court for the Eastern District of Michigan, the court denied GM's attempt to force the case into private arbitration, allowing the plaintiff to continue with litigation in a public court setting. This represents a critical juncture for those seeking further accountability regarding these transmission failures.