ZF S5-42 / S5-47

ZF's five-speed overdrive manual for Ford's heavy pickups — the gearbox the trade calls the ZF5. It arrived for 1987 in the F-350 cab and chassis and ran until 1997, when ZF's own six-speed S6-650 took over.

The two designations are the same gearbox at two torque ratings, and the numbers are the rating. The S5-42 is good for 420 lb-ft; the S5-47 is good for 470 lb-ft. That is where the alternative spellings S5-420 and S5-470 come from, and they name nothing different. The S5-42 ran from 1987 to 1994; the turbocharged Power Stroke outgrew its rating, and the slightly stronger S5-47 replaced it in diesel trucks from part way through 1994, standard for 1995 and retired after 1997.

The gear sets are not interchangeable between the two even though the gearboxes are. The S5-42 is the closer-ratio pair — 4.14, 2.37, 1.42, 1.00, 0.77 — where the S5-47 starts far lower at 5.08 and runs 2.60, 1.53, 1.00, 0.77. So a swapped truck will feel completely different in first and identical on the motorway, which is worth knowing before concluding that something is wrong.

The two will physically interchange without modification — but a petrol bellhousing pattern is not a diesel one, and that is the bolt-up that catches people out.

Almost everything reported as a gearbox fault on these is the hydraulic clutch. Grinding changes and rough engagement come from the release system far more often than from anything inside the case: a flexing firewall, worn pedal bushings, a worn master cylinder pushrod bushing, or air in the line. Bleed and inspect the clutch hydraulics before the gearbox is opened. Worn synchronisers do occur, reverse first.

A rollover rattle at idle in neutral is normal on a truck without a dual-mass flywheel. It is gear rattle, not a bearing.

It is an aluminium case and takes a little over three litres of Motorcraft MERCON V ATF — automatic transmission fluid in a manual gearbox, which surprises people. Gear oil in one of these is a mistake, not an upgrade.