The MGB GT V8 was fitted with a four-synchromesh manual gearbox closely related to the MGB 1800 4-synchro unit but with several V8-specific differences. The V8 gearbox uses a unique main casing (with a clutch housing profile to suit the rear engine plate of the V8), a V8-specific front cover (with the clutch release arm pivot relocated), a V8-specific breather, and a unique 1st motion shaft and laygear giving a closer-ratio gearset with a higher first gear than the standard MGB 1800. The four-synchromesh designation means all four forward gears have synchromesh engagement (the four-synchromesh unit replaced the earlier three-synchromesh gearbox on the MGB in 1968).
Synchromesh on All Four Gears
The four-synchromesh designation means all four forward gears have synchromesh engagement, first, second, third and fourth. Reverse is non-synchromesh and should be selected only with the car stationary. Synchromesh hubs and rings allow the gear teeth to mesh smoothly without crashing, with the synchroniser cone matching the speeds of the rotating components before the dog teeth engage.
Internal Components
The gearbox contains an input shaft (driven by the clutch), a layshaft running on bearings in the gearbox case, an output shaft (driving the propshaft), gear sets for each ratio, synchromesh hubs and rings, selector forks, and bearings throughout. Wear items in service include the synchromesh rings (which gradually lose effectiveness, causing the box to crunch into a particular gear), the bearings (which can develop noise or roughness), and the selector forks (where the contact faces wear, leading to the box jumping out of gear).
V8-Specific Bellhousing
The bellhousing is the V8-specific component of the gearbox assembly. It mates the gearbox front face to the Rover V8's flywheel housing, with starter motor mounting position and clutch fork pivot positioned to suit the V8 layout. The V8 bellhousing is not interchangeable with the four-cylinder MGB bellhousing.
Service and Rebuild
Gearbox rebuilds are specialist work involving disassembly, inspection and selective renewal of worn components. A complete rebuild typically includes new synchromesh rings, bearings, seals and gaskets, with selector forks, gear sets and shafts inspected and renewed only as needed. Reconditioned gearboxes are available on an exchange basis.
MGOC Spares
MGOC Spares supplies gearbox components, synchromesh kits, bearings, seals, selector forks and reconditioned gearboxes for the MGB GT V8.