General Motors 8L90 / 8L45

General Motors' longitudinal eight-speed — in the Corvette C7, the sixth-generation Camaro, the CT6 and CTS, the Colorado, and the Silverado, Sierra, Tahoe, Yukon and Escalade.

Its shudder is the best-documented complaint of any recent American transmission, and the useful part is what it is not. It is not a misfire, a driveline vibration or a tyre problem, though it is mistaken for all three: it is the torque converter lock-up clutch juddering, felt as driving over rumble strips at light throttle around 60–80 km/h, and it comes and goes with temperature before it becomes constant.

GM's own remedy was a change of fluid specification rather than a mechanical repair, which is the strongest available evidence about the cause — so on this transmission the fluid is the first thing to establish and the first thing to change, and a unit still on its original fill is the commonest version of this complaint.

The second recurring theme is harshness rather than slipping — a hard 2–3 change, a clunk on a downshift to a stop, a bump on the way into gear. These are valve-body and adaptation symptoms and they respond to a relearn far more often than to a strip-down.

It is not the 6L80. The eight-speed shares its platform and almost nothing else; the 6L80's signature failure — third, fifth and reverse lost together to a fractured wave plate — has no counterpart here.