The five-speed conversion is one of the most popular upgrades available for the MGB, transforming the driving experience by addressing the most significant limitation of the original transmission: the absence of a fifth, cruising gear. Whether your car retains the original three-synchro gearbox from the early chrome bumper years or the fully synchronised four-speed unit fitted from late 1967 onwards, a conversion kit is available to suit your specific car. The MGB was produced throughout its life with either a three-synchromesh or a four-synchromesh four-speed gearbox, with overdrive available as an optional extra across much of the production run. The three-synchro gearbox, fitted to cars from 1962 to late 1967, had synchromesh on second, third, and fourth gears only, first gear required a deliberate pause or double-declutch technique when changing down.
The fully synchronised gearbox was introduced with the Mark II model from late 1967, using engines of the 18GD type onwards, and remained in use through to the end of production in 1980. Both gearbox types are compatible with the five-speed conversion programme.
The Conversion
The five-speed conversion is based around the Ford Sierra Type 9 gearbox, a proven and well-supported unit. Kits include a new bell housing, revised gearbox crossmember, replacement propshaft, speedo cable, mountings, fittings, and full installation instructions. The Ford Sierra gearbox itself is not supplied as part of the conversion kit and must be purchased separately, MGOC Spares offer a reconditioned Type 9 unit as an outright purchase, supplied with new bearings, seals, gaskets, and all selected serviceable components.
The fifth gear ratio on this conversion is identical to the overdrive fourth ratio on the standard MGB Laycock overdrive unit, so owners already accustomed to overdrive cruising will find the fifth gear entirely familiar in feel and engine speed. The conversion also delivers a meaningful improvement in second gear acceleration, thanks to a higher second gear ratio than the original MGB gearbox, and the added benefit of synchromesh on all forward gears, including first. This last point is of particular relevance to owners of early three-synchro cars, where engaging first gear cleanly at low speeds has always required care.
Kit Selection
Selecting the correct kit requires knowing both the year of your car and, for earlier roadsters, which rear axle type is fitted. Roadsters built up to the end of 1964 (18G and 18GA engines) use a specific RHD or LHD kit. Roadsters from 1965 to 1967 are split further, those with the earlier banjo-type rear axle use a dedicated RHD or LHD kit, while cars fitted with the tube-type axle take a separate RHD or LHD kit.
Note that the banjo axle was used on roadsters built up to approximately July 1967, while the GT used the tube axle from the start of its production in September 1965. From 1969 to 1975, RHD and LHD kits apply, with RHD and LHD kits covering 1976 to end of production rubber bumper cars. All kits are handed for right-hand or left-hand drive, and it is important to select the correct variant.
If there is any uncertainty about the rear axle type on a 1965 to 1967 roadster, this should be confirmed before ordering, as the propshaft length within the kit differs between applications. The MGOC Spares range covers the full selection of five-speed conversion kits along with the reconditioned Ford Sierra Type 9 gearbox, ensuring both components can be sourced together for a straightforward, reliable installation.