The three-synchromesh gearbox was fitted to the MGB from the start of production in 1962 through to the end of three-synchro production in late 1967, covering all cars with 18G, 18GA, and 18GB engine series. This external components section covers the complete gearbox assemblies, gear levers and knobs, casing gaskets and seals, speedo drive components, and all associated ancillary hardware for these cars.
Gearbox Variants
Two distinct versions of the three-synchromesh gearbox exist, reflecting the change in engine specification during this period. Cars with 18G and 18GA engines, produced from 1962 to October 1964, used a three-main-bearing crankshaft engine, and the gearbox first motion shaft for this engine has an input spigot diameter of 0.62 inch.
From October 1964, the 18GB engine introduced a five-main-bearing crankshaft along with a larger input spigot of 0.85 inch, requiring a modified gearbox casing. These two gearbox variants are not interchangeable and reconditioned units are listed separately by engine series. Within the five-main-bearing 18GB period, the catalogue further distinguishes between early and late three-synchro units, reflecting minor internal evolution across the production run. Overdrive and non-overdrive gearboxes also differ externally, as the overdrive-equipped gearbox terminates the rear extension early and uses an overdrive adaptor housing in place of the conventional rear extension.
The reconditioned assemblies offered by MGOC Spares are listed accordingly, non-overdrive and overdrive variants are separate part numbers, and customers should identify their engine series and overdrive fitment before ordering. The MGOC Spares range includes two tiers of reconditioned gearbox: a standard reconditioned unit and a premium quality unit which includes a greater number of new components above and beyond the standard reconditioning scheme. For three-main-bearing (18G/18GA) non-overdrive cars, the standard unit is supplied on a one-for-one exchange basis. For overdrive-equipped three-main-bearing cars, and all five-main-bearing variants, the reconditioned units are on a customer own unit basis, meaning customers must supply their original unit for rebuilding.
A Ford Sierra Type 9 five-speed gearbox is also available as an outright purchase and forms the basis of the five-speed conversion kits available for three-synchro cars, these are covered in the Upgrades & Alternatives section.
Gear Lever & Ancillaries
The gear lever fitted to three-synchromesh cars has a distinctive shape with a double bend, giving the lever an inclined angle to the rear. On overdrive cars the lever has a single bend, keeping the upper portion and knob inclined rearward. A gear knob in the 5/16 UNF thread size is available in black for three-synchro cars, along with the original teardrop-shaped gear knob with gate markings correct for non-overdrive applications. External components available include the gearbox rubber pad, gearbox-to-engine bolt kit, front cover oil seal, front cover gasket, side cover gasket, drain plug, gear case to rear case/overdrive gasket, top cover to rear case gasket, gear case to rear case non-overdrive gasket, overdrive-to-gearbox gasket, reverse/overdrive isolation switch, fibre washers, speedo pinion housing gasket, speedo pinion oil seal, right-angle speedo cable drive adaptor, gear lever swivel retaining cover, gear lever retainer securing circlip, gearbox/rear axle breather, and all associated fixings.