The MGA clutch is hydraulically operated. Pressing the clutch pedal moves a piston in the master cylinder, which displaces hydraulic fluid through a rigid pipe (with a short flexible hose section at the slave end) to the slave cylinder mounted on the bellhousing. The slave cylinder piston then moves the clutch fork through its pushrod, lifting the release bearing against the pressure plate and disengaging the drive. The hydraulic system is distinctive on the MGA because of a significant ordering split: pushrod-engined cars other than the De Luxe use a combined brake-and-clutch master cylinder that operates both circuits from a single shared fluid reservoir, while Twin Cam and De Luxe cars use a separate clutch master cylinder alongside the brake master cylinder.
This is the most important identification point when ordering clutch hydraulic components.
Master cylinder, combined versus separate
The combined master cylinder fitted to pushrod non-De-Luxe cars operates both the brake and clutch circuits from one unit with one fluid reservoir. The reservoir is divided internally so that a leak in one circuit does not completely empty the other, but the two share the same fluid supply and the same cylinder body. Twin Cam and De Luxe cars have a separate clutch master cylinder with its own reservoir, operating only the clutch circuit, alongside a separate brake master cylinder operating the brake circuit. The two arrangements are not interchangeable: the cylinder body pattern, mounting, piston diameter and reservoir layout all differ.
Master cylinder types
Three main master cylinder patterns were used during MGA production. The 1500 type was fitted to pushrod 1500 cars. The 1600 and 1600 Mk II type has a raised cover over the supply reservoir, visually the most obvious difference from the 1500 type. The Twin Cam and De Luxe type is mounted turned on its side, quite different in orientation from the pushrod items.
Replacement master cylinders, reservoir caps, rebuild kits and the mounting hardware are all available for each of the three patterns. When ordering, the chassis number and variant identity (pushrod non-De-Luxe, pushrod De Luxe, or Twin Cam) determine which pattern suits the car.
Slave cylinder, pushrod 1500
The slave cylinder on pushrod 1500 cars is mounted on the right-hand side below the bellhousing and pushes the clutch fork via a short pushrod. The 1500 slave cylinder was revised at car/chassis 11768, when a simplified housing without a separate banjo was introduced.
Earlier 1500 cars (pre-11768) use the original banjo-type housing; later 1500 cars and subsequent 1600, 1600 Mk II, Twin Cam and De Luxe cars do not. Replacement slave cylinders, seal kits and pushrods are available for both patterns.
Slave cylinder, Twin Cam and De Luxe
The Twin Cam slave cylinder is of a completely different design from the pushrod pattern, reflecting the Twin Cam's different bellhousing and clutch fork geometry. It was not subject to any production-change revisions during Twin Cam production, a single specification serves the whole Twin Cam range. The De Luxe variants of the 1600 and 1600 Mk II use the Twin Cam-pattern slave cylinder rather than the pushrod type, consistent with their use of Twin Cam-derived clutch hydraulics.
When ordering a slave cylinder, confirming whether the car is a Twin Cam, a De Luxe, or a standard pushrod car is essential.
Rigid pipes, flexible hoses and hardware
The hydraulic circuit between master and slave cylinders uses a rigid pipe running along the chassis for the majority of its length, with a short flexible rubber hose at the slave cylinder end to accommodate clutch fork and engine movement. Both are routine service items: rigid pipes can develop pinhole corrosion externally, and flexible hoses harden, craze and eventually fail internally with ageing rubber. A flexible hose that has deteriorated internally can act as a one-way valve, allowing fluid to pass under pedal pressure but restricting return flow, causing the clutch to not fully re-engage when the pedal is released.
Replacement rigid pipes, flexible hoses, union fittings and the small mounting hardware are all available as service items.
Seals, rebuild kits and fluid type
Master cylinders and slave cylinders can be rebuilt with seal kits rather than replaced complete, provided the cylinder bore is not pitted. Seal kits include the primary and secondary cup seals, the rubber boot on the external end, and the small spring and clip hardware. Cylinder bores that have pitted internally from long service or from water contamination of the fluid cannot be reliably returned to service by reseal alone, a fresh cylinder is the appropriate fix.