Aisin AW50-42LE

Aisin's transverse four-speed for Volvo — in the 850, S40, C70 and V70 of the 1990s.

It is the AF33's predecessor and shares its failure, which is the useful part: the valve body wears its bores, line pressure falls, and the clutches stop being held firmly. The symptom sequence is the same and is still the thing to catch — a slightly delayed engagement into drive when cold, then a flare on one particular change, then slipping.

Nothing about the early stage feels like the start of a failure, and by the time it does the clutch packs are usually gone. Sleeving the bores is a recognised repair and is far cheaper than a replacement, but only while there is something left to save.

These transmissions are old enough that fluid history is unknowable, and the whole failure is hydraulic — a fluid that has lost viscosity accelerates the wear that causes the pressure loss that ruins the clutches. A pan drop tells more in ten minutes than any amount of scanning.

The turbocharged five-cylinder cars are hardest on it, which is exactly the population that survives; a T5 with an unknown gearbox history is the commonest version of every complaint above.