The MGB GT V8 drivetrain combines a V8-specific clutch, a four-synchromesh manual gearbox with overdrive fitted as standard, an open propshaft, and a tube-type rear axle with 3.071:1 final drive. The V8 gearbox is the four-synchromesh MGB 1800 unit fitted with a V8-specific bellhousing casing to suit the Rover V8's flywheel and clutch arrangement. The overdrive unit is the LH (Laycock 'D' Type LH) overdrive, mounted on the gearbox tail housing and engaged by a column-stalk switch.
Clutch
The V8 uses a clutch sized for the Rover V8's torque output, with a different friction-disc and pressure-plate specification from the four-cylinder MGB clutch. The clutch hydraulics use a master cylinder on the bulkhead and a slave cylinder at the gearbox bellhousing, sharing fluid with the brake hydraulic system reservoir on early cars and using a separate clutch reservoir on later cars.
Gearbox and Overdrive
The four-synchromesh gearbox includes synchromesh on all four forward gears (a step up from the earlier three-synchromesh gearboxes used on the MGB up to 1968). The Laycock 'D' Type LH overdrive is fitted as standard, providing an overdrive ratio (on top gear from gearbox 1404 onwards; early production cars to gearbox 1403 had overdrive on third and fourth), with the column-stalk switch giving the driver control. The overdrive is engaged by an electrical solenoid that operates a hydraulic valve in the overdrive unit, with the solenoid receiving power through gearbox-mounted inhibitor switches that prevent engagement in the wrong gears.
Propshaft and Rear Axle
The propshaft is an open type with universal joints at each end, transmitting drive from the gearbox tail to the rear axle pinion flange. The rear axle is the tube-type Salisbury-style axle with hypoid gears and a 3.071:1 final drive ratio (14-tooth pinion driving 43-tooth crown wheel). The axle case carries the road wheels at each end via half-shafts running in bearings at the hubs.
Sub-Sections
Clutch System and Clutch Hydraulics cover the clutch components. Gearbox covers the four-synchromesh transmission. Overdrive covers the Laycock LH overdrive unit. Propshaft and Rear Axle and Diff (Tube) cover the rest of the drivetrain. Classic Gear Oils covers the appropriate lubricants.
Clutch and Brake Fluid covers the hydraulic fluid. Upgrades and Alternatives cover Five Speed Conversions and other upgrade options.
MGOC Spares
MGOC Spares supplies the full range of MGB GT V8 drivetrain components, see individual sub-sections for details.