The four-synchromesh gearbox was fitted to the MGB from the start of Mark II production in late 1967, continuing through to the end of production in 1980. It covered all 18GD, 18GF, 18GG, 18GH, 18GJ, 18GK, and 18V engine series, and was also used in the MGB GT V8 with a different casing to accommodate the larger clutch. This external components section covers complete reconditioned gearbox assemblies, gear levers and knobs, gaiters, casing gaskets and seals, speedo drive components, and associated ancillary hardware.
Reconditioned Gearboxes
The four-synchromesh gearbox underwent one notable external casing change during its production life. From the start of rubber bumper production in 1974, the gearbox casing was revised with a side-mounted filler plug replacing the previous combined filler and dipstick arrangement at the top.
This change took effect from engine numbers 18V846, 847, 797, 798, 801, and 802 onwards. The two casing types are not interchangeable and reconditioned units are listed separately for chrome bumper and rubber bumper applications. The MGOC Spares range includes reconditioned four-synchromesh gearboxes across non-overdrive and overdrive variants in both chrome bumper and rubber bumper specifications, in both standard and premium quality reconditioning tiers.
The chrome bumper non-overdrive standard unit and rubber bumper standard units are on a one-for-one exchange basis, while the premium quality rubber bumper non-overdrive unit is available as a customer own unit.
Gear Lever & Knob
The gear lever and knob arrangement changed several times across the four-synchromesh production run and these changes are relevant when sourcing replacement items. The original Mark II gear lever is a straight, vertical unit with a ball-shaped knob, and this lever was used from 1967 until September 1976.
From September 1976 the lever was cranked rearwards and fitted with a larger mushroom-shaped knob of the type used on Triumph cars, which on overdrive-equipped cars incorporated the overdrive switch in the top of the knob. Two gear knobs are listed for the earlier period: an early round knob with gate markings covering the Mark II era, and the larger standard BL-type gear knob used from October 1972 through to September 1976. The gear knob retaining nut suits pre-September 1976 cars. For September 1976-on cars, the retaining nut, overdrive switch, gear knob cap with printed gate, non-overdrive gear knob cap, and overdrive wiring harness extension are all available.
An overdrive gear knob for chrome bumper four-synchro cars, carrying the switch in the 3/8 inch thread size, is also available.
Gaiters, Gaskets & Ancillaries
Gear lever gaiter options are available as vinyl (fitted from October 1971 onwards) or as a gaiter and seal assembly. The chrome gearlever retaining ring and the later black retaining ring (September 1976 on) are both available, along with the gear lever selector yoke nylon bush and anti-rattle plunger with spring and washers. Casing gaskets available include the front cover gasket, front cover oil seal, gearbox side cover gasket, remote housing to rear extension gasket, overdrive adaptor to gear case gasket, overdrive unit to gearbox gasket, non-overdrive rear extension to gear case gasket, and speedo pinion housing gasket. A gearbox drain plug and gearbox/rear axle breather are available, along with the reverse/overdrive isolation switch, the gearlever retaining plate bolt, and all associated fixings.
The right-angle speedo cable drive adaptor and speedo pinion oil seal complete the speedo drive component range on this page.