Two entirely different four-speed manual gearboxes were used in the Midget. The BMC A-Series ribcase gearbox was fitted to all 1098cc and 1275cc cars, while the Triumph single-rail gearbox was fitted to the 1500. No internal or external components are shared between the two designs, so identifying the correct gearbox before ordering any parts is essential.
A-Series Gearbox
The A-Series gearbox is a four-speed unit with synchromesh on second, third, and fourth gears only. First gear is non-synchromesh with straight-cut teeth, requiring the car to be fully stopped or double-declutched for the change. The gearbox is mounted directly to the engine backplate and carries a remote selector housing on the rear extension, which houses the gear lever and associated anti-rattle components.
A-Series Gear Lever
The gear lever anti-rattle mechanism (sometimes called the "zizzle kit") consists of bushes, plungers, springs, and a button that dampen the fine vibrational rattle common at cruising speeds or on the overrun. These components wear quickly and are a straightforward renewal carried out from within the passenger compartment, accessible through the remote housing without removing the gearbox from the car.
A-Series Front Cover
The front cover of the A-Series gearbox is not oil-tight around a stationary input shaft. If only the rear of the car is jacked up, oil will dribble from the front cover, down the bell housing, and onto the floor. This is normal and not a sign of seal failure. The correct procedure when working under the rear of the car is to jack up the front end first, then the rear, to keep the gearbox level or slightly nose-up.
A-Series Internals
Key internal components include the synchro rings (three fitted, for second, third, and fourth gears), the laygear and layshaft, selector forks, and the first motion (input) and third motion (output) shaft bearings. A complete gearbox rebuild kit containing bearings, synchro rings, gaskets, and seals is available. The speedo pinion is driven from the gearbox and is available in different tooth counts to match the final drive ratio and tyre size.
1500 Gearbox Design
The 1500 gearbox is a fully synchromesh four-speed unit, with synchromesh on all four forward gears including first, an improvement over the non-synchro first gear on the A-Series box. The selector mechanism is a single-rail design, meaning a single selector shaft operates all four gear positions, which gives a different shift feel compared to the A-Series unit.
1500 Front Cover Variants
Two front cover types were produced, distinguished by their sealing arrangement. The oil seal type was fitted to gearbox numbers up to 59162, and from 60001 to 65224. The oil thrower type was fitted from 59163 to 60000, and from 65225 onward. The front covers and their seals are not interchangeable between the two types, so the gearbox number must be checked before ordering front cover components or oil seals.
1500 Internal Components
The 1500 gearbox has four synchro rings rather than the three on the A-Series, reflecting the full synchromesh on all gears. The laygear was revised during production, with an improved design introduced from gearbox number 241364 onward.
The first motion shaft also changed, with two variants distinguished by their bearing arrangement. A gearbox rebuild kit is available containing all the bearings, synchro rings, gaskets, and seals needed for a complete overhaul.
1500 Gear Lever
The gear lever on the 1500 is a different design from the 1275cc, with its own unique grommet, gaiter, and retainer plate. The gearlever retainer changed from June 1978 onward. A range of aftermarket gear knobs in wood, leather, aluminium, and carbon-effect finishes are available for both gearbox types.
External Components & Gasket Sets
External gearbox components include the front cover and oil seal, the rear extension housing and oil seal, the speedo pinion housing and pinion, the reversing light switch, and the drain and filler plugs. The gearbox gasket set covers the external gaskets needed when removing the gearbox from the car or when replacing the remote housing or side cover. These gaskets differ between the A-Series and Triumph units, so the engine type must be specified when ordering.