Ford AOD

Ford's first four-speed automatic, and the last one it built with no electronics in it at all. Behind every rear-drive Ford of the 1980s — the Mustang, the Thunderbird, the Bronco, the F-Series, the Panther saloons and the Town Car.

⚑ The AOD and the AOD-E are not the same gearbox, and the names are one character apart. They share pans, cases, bellhousings and most internals, and they are not interchangeable: the AOD decides when to shift hydraulically, from a throttle valve rod worked by the accelerator linkage, while the AOD-E is told when to shift by the engine's control module. A part number, a diagnosis or a rebuild kit quoted for "the AOD" is worth nothing until somebody says which, and a 1993 car and a 1994 car of the same model can be either.

That rod is the thing to check first, and it is the commonest way one of these dies. It sets line pressure as well as shift timing, so a rod that is loose, stretched, disconnected or wrongly adjusted after an engine swap does not merely shift badly — it starves the clutches of pressure and burns the transmission out, often within a few hundred miles. Soft, late, slipping shifts on an AOD are a linkage adjustment until proven otherwise.

Third gear is split between two paths, which is the other thing that makes it unusual. A direct input shaft drives part of the torque mechanically while the rest goes through the converter, which is where its fuel economy came from and why its input shafts are a known failure on a car making more power than Ford intended.

Ratios are 2.40, 1.47, 1.00 and 0.67, with a 2.00 reverse. It became the AOD-E in 1992 and then the 4R70W, both of which have their own page here.