All MGAs use an 8-inch Borg & Beck single dry-plate clutch with hydraulic operation. Pushrod-engined cars (1500, 1600 and 1600 Mk II) use the A6-G clutch specification; the Twin Cam uses the 8ARG specification. The two are not interchangeable, and several production-change breakpoints within the pushrod range further refine which individual components, pressure plate, driven plate, clutch fork, pedal, suit which chassis number. Ordering clutch components accurately therefore depends on the engine prefix and, for some items, the specific chassis number of the car.
Clutch assembly construction
The clutch assembly comprises a pressure plate (the cover assembly with its coil pressure springs and release mechanism), a driven plate (the friction disc that rides on the gearbox first motion shaft splines), and a release bearing (the thrust bearing that translates clutch-pedal movement into clutch disengagement). The assembly sits within the bellhousing between the engine flywheel and the gearbox input shaft. The pressure plate clamps the driven plate between itself and the flywheel through the action of the coil pressure springs; operating the clutch pedal via the hydraulic master and slave cylinder moves the release bearing against the pressure plate's fingers, lifting the clamping load off the driven plate and disengaging the drive. The MGA Borg & Beck design uses coil pressure springs rather than the diaphragm spring found on later clutches.
Pressure plate and cover assembly
The pushrod A6-G pressure plate was revised during 1500 production: from engine number 15GB/16226, stronger pressure springs and a modified cover assembly were introduced. Earlier 15GB engines use the original lighter-spring specification.
Cars built after 15GB/16226, through the end of 15GD, 16GA and 16GC production, use the later specification. The Twin Cam 8ARG pressure plate is a different unit altogether and was not subject to any important production changes during Twin Cam production.
Driven plate
The standard MGA driven plate carries six damper springs around its hub. An alternative four-damper-spring driven plate was introduced partway through 1500 production, referenced in Factory Service Memorandum MG/226 (July 1958), though the factory did not record the specific engine number change point, both types may be encountered on 1500 cars of a period. The 1500 Parts List gives only the six-spring item. On the 1600 Mk II, the driven plate was revised from engine number 16GC/3929 to suit a gearbox first motion shaft with finer splines.
Fitting a pre-16GC/3929 driven plate to a first motion shaft cut to the later finer-spline specification, or vice versa, results in the plate either not engaging the shaft correctly or damaging the splines on first operation. When ordering a driven plate, the engine number should be checked against this breakpoint.
Release bearing
The release bearing is a thrust bearing that operates the clutch finger mechanism when the pedal is pressed. It is a wear item in normal service and should be renewed whenever the clutch is disturbed, regardless of apparent condition, the labour to access the bearing is identical whether the bearing is being inspected, lightly refreshed or fully replaced, and refitting a used bearing into a new clutch installation is false economy.
Replacement release bearings are available as service items for both pushrod A6-G and Twin Cam 8ARG installations.
Clutch fork and withdrawal lever
The clutch fork (withdrawal lever) transfers slave-cylinder movement to the release bearing. On pushrod 1500 cars, the clutch withdrawal lever was modified at engine number 15GB/4525, with a larger-diameter clutch fork pivot bolt introduced from that point.
Replacement forks and pivot bolts should be ordered to match the pre- or post-15GB/4525 specification of the car. The Twin Cam uses a different fork and pivot arrangement appropriate to the 8ARG clutch.
Clutch pedal
All MGAs use a pendant clutch pedal with a shield-shaped rubber pad carrying vertical ribs, matching the brake pedal pad. Three pedal patterns were used during production: an early right-hand drive 1500 type, a later right-hand drive 1500/1600 type (introduced on RHD cars from chassis 61100), and a left-hand drive type (revised on LHD 1500s from chassis 58713). The Twin Cam and De Luxe variants use a pedal with the arm extending further above the pivot point, though the pedal rubber is common with the pushrod pattern. Identifying which pedal is fitted helps confirm a car's specification as part of a restoration or sale inspection.
Ordering considerations
Ordering begins with the engine type, pushrod A6-G or Twin Cam 8ARG.