General Motors 6L80 / 6L90 / 6L45

General Motors' longitudinal six-speed — in the Corvette, Camaro, Silverado, Sierra, Tahoe, Escalade, Commodore and, as the smaller 6L45, in BMW's E87 and E90.

Its characteristic failure has a name and a very specific symptom: the 3–5–reverse wave plate. The plate fractures, and the transmission loses third, fifth and reverse together while first, second, fourth and sixth still work. That combination is the diagnosis — no other common fault takes exactly those three, and a car that drives forward normally but will not reverse is not a linkage problem.

GM revised the plate, so which one a unit contains decides whether the repair is a rebuild or a replacement, and a transmission that has already been apart may or may not have received it.

Torque converter shudder is the other recurring complaint — a light vibration under gentle throttle at low speed, often described as driving over rumble strips. It tracks fluid condition closely, and on this unit a fluid change is a diagnostic step rather than only maintenance.

The 6L45 in a BMW is the same family and a different size. Parts and capacities differ, and a procedure written for a Silverado's 6L80 does not describe it.