Ford SROD

Ford's Single Rail OverDrive four-speed — the manual gearbox the Fox-body Mustang launched with in 1979 and kept through 1982, and which stayed in the light trucks a few years longer.

The name describes the mechanism and it is the unusual part. Where almost every four-speed of the period moved its gears with three separate shift rails, the SROD uses one, with a single rail doing the selecting as well as the shifting. It is a departure from the H-pattern hardware around it, and it is why its internals do not resemble a Toploader's at all despite both being Ford four-speeds of the same decade.

It exists because of fuel economy rather than performance. The fourth ratio is an overdrive, added to drop motorway revs at a moment when that was the priority; the gearbox is a wide-ratio unit in an aluminium case with synchromesh on all four forward gears.

Its limit is the reason nobody keeps one. It was never rated much beyond 200 lb-ft, which is adequate behind the engines the 1979–1982 cars actually came with and nowhere near enough behind anything built since. A modified engine will destroy one, and the near-universal advice is to fit the Borg-Warner T-5 that replaced it from 1983.

That swap is not a drop-in. Going from an SROD to a T-5 means changing the flywheel and the bellhousing as well as the gearbox, and the speedometer drive gear with them — the SROD's is a different tooth count. Budget for all four.