External gearbox components on an MGA include the gear lever and its knob and gaiter, the remote control housing at the rear of the gearbox extension, the left-hand side cover of the gearbox casing, the rear extension oil seal, and the gearbox dipstick. The complete gearbox casing, including the bellhousing, rear extension and remote control unit, is left unpainted from the factory.
Replacement external components are available as service items for all MGA variants, with the most frequently renewed items being the rear extension oil seal and the various gaskets that seal the cover plates and remote control housing to the main casing.
Gear lever, knob and gaiter
The MGA gear lever is chrome-plated and carries a black pear-shaped Bakelite knob with the shift pattern, the standard H gate, with reverse to the left and back, engraved in white. A rubber gaiter fits around the lever where it passes through the carpet into the gearbox tunnel, sealing the tunnel opening against drafts and road debris.
Replacement levers, Bakelite knobs and gaiters are available as service items.
Remote control housing
The remote control housing is a named factory assembly mounted at the rear of the gearbox casing, carrying the selector mechanism between the gear lever and the gear-change rails within the gearbox. It is finished as part of the unpainted gearbox casing. The housing-to-casing joint is sealed by a gasket; replacement gaskets, the housing casting itself, and the selector hardware inside it are available as service items.
Left-hand side cover
The gearbox main casing has a detachable side cover on the left-hand side of the gearbox, giving access to part of the gear-change mechanism without requiring a full internal strip. The cover is a plain casting sealed against the main casing with a gasket. The side cover gasket is a common service item and should be renewed whenever the cover is removed.
Rear extension oil seal
The oil seal at the rear of the gearbox extension, where the output shaft passes out of the casing to drive the propeller shaft, is an area where the MGA had problems during production. No fewer than five different oil seal types were used on the 1500 alone as the factory sought to address persistent leakage, and the correct seal for a specific gearbox depends on its individual specification. The five-seal history means a replacement seal must be matched to the seal arrangement fitted to the gearbox rather than assumed from the engine or chassis number. The specific change points for these seal types are documented in specialist literature rather than in the factory parts lists.
Dipstick
The gearbox dipstick is fitted on the right-hand side of the gearbox casing. It is accessed from inside the car rather than from under the bonnet: the dipstick emerges through a rubber plug in the gearbox tunnel on the right-hand side, covered by a flap in the carpet. The gearbox number is stamped into the casing adjacent to the dipstick location. Gearboxes were individually numbered with four-figure numbers and varying letter prefixes, though the precise factory numbering convention has never been fully decoded.
Gearbox tunnel production change
The gearbox tunnel itself, the floor pressing between the gearbox and the cabin, changed between early and later 1500 cars. Early 1500 cars fitted with the 15GB engine use the original tunnel specification; later cars fitted with the 15GD engine from January 1959 onwards use a revised tunnel with an extra rubber cover "blip" necessitated by the raised starter position introduced with the 15GD.
The revised tunnel then continued unchanged onto all subsequent pushrod MGAs and onto Twin Cam cars. When replacing the tunnel as part of a restoration, the correct tunnel pattern for the engine fitted must be selected.
Ordering considerations
External gearbox components are largely serviceable with the gearbox still fitted to the car, which makes them the most frequent service-item orders in the gearbox area. Oil seal orders require matching the seal specification to the gearbox itself rather than to the chassis number alone, the gearbox number stamped adjacent to the dipstick is the starting point for confirming specification. Gaskets (remote control housing, side cover, rear extension plate where applicable) should all be renewed whenever their respective covers are removed, and are commonly ordered together as a gasket-set rather than individually.