This section covers performance and alternative drivetrain components for the MGB, spanning final drive ratio changes, five-speed gearbox conversions, and the tools required for clutch work, allowing owners to improve performance, refinement, or usability while retaining the fundamental character of the car. The three categories address the clutch, gearbox, and rear axle respectively, each with a distinct purpose.
Crown Wheels & Pinions
Crown wheels and pinions allow the final drive ratio to be altered from the standard 3.909:1 (11/43 teeth). For the banjo axle, alternative ratios of 4.3:1, 4.55:1, and 4.875:1 are available, all progressively shorter gearing that improves acceleration at the expense of cruising rpm. For the Salisbury tube axle fitted to all GT models from 1965 and all roadsters from 1967, a 3.07:1 conversion set is available, providing noticeably taller gearing, equivalent to the 14/43 MGC and MGB GT V8 final drive, that reduces engine speed at motorway cruising and is particularly effective when combined with a five-speed conversion or overdrive. Crown wheel and pinion sets are axle-specific and not interchangeable between banjo and tube axle cars, are manufactured in the UK, and can be supplied outright or built into a customer's own axle unit.
Five Speed Conversions
Five speed conversions use the Ford Sierra Type 9 gearbox to replace the original three or four-synchro unit, providing synchromesh on all five gears, a more usable close-ratio spread through the lower gears, and a fifth gear ratio equivalent to the standard MGB overdrive fourth. The kit uses a purpose-made adaptor bell housing, crossmember, propshaft, and speedo cable, though the Sierra gearbox itself is not included and is available separately as a reconditioned unit. Kits are available for all MGB variants from 1962 onwards, early three-synchro cars distinguishing between banjo and tube axle where applicable, four-synchro chrome bumper cars, and rubber bumper cars from 1976, each requiring a different kit.
Clutch Tools
Clutch tools include the alignment tools required for correct clutch plate centring during fitment. Correctly aligning the clutch plate on the flywheel before the gearbox is refitted is essential, as without alignment the gearbox input shaft will not pass cleanly through the clutch plate spigot hole and the gearbox cannot be fully seated. The alignment tool replicates the profile of the gearbox first motion shaft and allows the plate to be centred accurately before the cover bolts are tightened. Two variants are listed, one for the 18G and 18GA three-main-bearing engines from 1962 to 1964, and one for the five-main-bearing 18GB, GD, GG, and 18V engines from 1965 onwards, reflecting the change in first motion shaft spigot diameter introduced with the 18GB engine in October 1964.