Aisin TF-80SC

Aisin's large transverse six-speed automatic, rated to 450 Nm, and one of the most widely sold gearboxes in Europe that almost nobody can name. Volvo, Saab, Opel, Peugeot, Citroën, Renault, Alfa Romeo, Lancia, Cadillac and Chevrolet all bought it, which is why it turns up under more different manufacturer codes than any other unit here — TF-80SC, TF-81SC, AF40-6, AM6, AW6A-EL and AWF21 are one gearbox with six badges.

It is not the 09G, and confusing the two is the commonest mistake made about it. Aisin's transverse six-speeds come in two sizes: the TF-60SN, rated for around 280 Nm and fitted to Volkswagens, SEATs, Škodas and Minis, and this one, rated for 450 Nm and fitted to the heavier cars above. The designations differ by one digit and the gearboxes are different machines with different parts, so the number matters more than the fact that both say Aisin.

Like the smaller unit it uses a Lepelletier gearset, which is how it delivers six ratios with fewer components than the five-speeds it replaced. Two design details are worth knowing because they shape what fails: the torque converter locks up in all six gears rather than only the upper ones, and the control module sits inside the case, in the fluid, to cut the external wiring.

The single most useful fact about this gearbox is that its worst fault was fixed partway through production. Early units were built with a torque converter whose housing metal was too thin: the damper springs shifted under load, the lock-up clutch then wore unevenly, and the result is the vibration owners describe as a shudder at light throttle. Units built after about 2010 are markedly better and shed most of this reputation. So the year matters when judging a car — the fault is real, and it is not evenly distributed across the run.

The valve body is where the money goes, and one detail is worth knowing before agreeing to a repair. What wears is not usually the solenoids but the bores the valves ride in: once those are worn, fluid cross-leaks between circuits, and no amount of reprogramming or adaptation resetting will compensate for a leak. A shop offering a software fix for a gearbox with worn bores is offering something that cannot work.

The rest follows the pattern of any torque-converter automatic asked to work hot:

• Clutch pack wear in the hydraulic block, which is what the contaminated fluid then carries everywhere.
• A clogged heat exchanger, which stops cooling the fluid that is carrying the debris — the loop that accelerates itself.
• Brake band and overrunning clutch bearing wear, which arrive last and mark the point where a repair becomes a replacement.

The fluid is the whole of its maintenance and it was not sold as a service item. It takes an ATF JWS-3324 type — Aisin AW-1 or Toyota WS — and the interval that keeps one alive is on the order of 60,000 km. The unit is intolerant of a substitute fluid in a way that a larger, better-cooled gearbox would forgive.