Hyundai D8LF1 (8DCT)

Hyundai's wet eight-speed dual-clutch — in the Elantra N, Kona, Santa Fe, Sonata and Veloster N, and the Kia equivalents.

It exists because of the seven-speed's weakness, and that is the most useful thing to know about it. The D7UF1's clutches run dry and overheat when the car is held on a hill or crept through traffic; these run in oil, which carries the heat away, and the low-speed judder that defines its predecessor is not a characteristic of this gearbox.

So a hesitation or a shudder from rest on a wet eight-speed is a fault, where on the dry seven-speed it is often the design meeting a driving habit. That inversion is worth stating plainly, because advice written about the 7DCT circulates freely and gets applied to this one.

Its own theme is fluid and the mechatronic unit. A wet dual-clutch shares its oil between the clutches and the hydraulics that operate them, so fluid condition is not a maintenance question here but a control question — worn fluid makes the gearbox change badly before it makes anything fail.

Its faults present electrically: a gear refused, a limp mode, a code naming a solenoid or a clutch position sensor. Nothing slips first.