The AC-Engined Car's Gearbox: the Moss Box and the 2-Litre
A question that comes up often among AC-engined car owners: is the early Ace or Aceca gearbox the same as the one in the AC 2-litre saloon? Largely, yes. It is the same Moss box, but there are a few differences that matter if you are sourcing or swapping one. Here is what is shared, what is not, and what it takes to make a 2-litre box work in an Ace.
Confirm against your car
This applies to AC-engined cars, those with AC's own Light Six engine. Bristol-engined and 2.6-litre Ford-engined cars have different transmissions. Confirm against your own car, and leave gearbox internals to a specialist.
The Moss box is shared, with differences
The Moss gearbox in the early AC-engined Ace and Aceca is essentially the same unit as the AC 2-litre saloon's. The differences are around it rather than inside it. The Ace and Aceca have a hydraulically-operated clutch, where the 2-litre's clutch pedal joins directly to a cross-shaft. The gear lever is much shorter, to clear the dashboard. And the gearstick turret is shorter too, for clearance over the gearbox tunnel, the same short turret used on the Morgan boxes of the period.
Fitting a 2-litre box to an Ace
Because of the clutch difference, dropping a 2-litre box into an Ace is not a straight swap. The hydraulic clutch actuation has to be accommodated, reworking or jigging the shaft arrangement and adding a slave-cylinder stay bar to locate the hydraulics. It is a known conversion, but plan for that adaptation rather than expecting a bolt-in.
In short
The early AC-engined Ace and Aceca use the same Moss gearbox as the AC 2-litre saloon, distinguished by a hydraulic clutch, a shorter gear lever and a shorter turret for tunnel and dashboard clearance. A 2-litre box can be used, but the clutch actuation must be adapted with a reworked shaft and a slave-cylinder stay bar. As always, confirm against your own car.
Sources. This article draws on the experience of owners in the AC Owners' Club community. No endorsement is implied.
A general guide to the AC-engined car's gearbox, not a substitute for the workshop manual or a gearbox specialist. Confirm details against your own car, and have internal work done professionally.
About the author
A lifelong classic-car enthusiast in North Yorkshire, near Thornton-le-Dale, who owns and maintains an AC Aceca, writing the single-model reference he always wished existed. Read the full bio.