Ford C6

Ford's heavy-duty three-speed automatic — in the F-150 and the Bronco.

It is the TH400's opposite number and shares its standing: enormously strong, very simple, and still fitted behind engines making far more power than Ford ever put in front of it.

Three ratios and no overdrive is the design. A C6 revving hard at motorway speed is doing what it was built to do; there is no fourth gear to be missing, and this is the commonest reason one is looked at.

Its faults are age rather than wear. The governor drifts, producing changes at the wrong road speed; the modulator — a vacuum-operated part — does the same and can be tested with a hand pump in minutes; and the front pump seal leaks. A gearbox that changes consistently too early or too late is one of those two, and that is a very different problem from slipping.

These are old enough that fluid history is unknowable and usually poor, and a pan drop tells more in ten minutes than any amount of scanning.