The single-circuit system fitted to UK and most export MGCs uses a single brake master cylinder feeding all four wheel brakes through a four-way adaptor, a three-way adaptor, and the brake light switch. A single Girling servo provides vacuum assistance. The brake and clutch pipes run together through the car, and a complete copper pipe kit covers both circuits in a single set. Flexible rubber hoses, two at the front wheels and one at the rear axle, accommodate suspension and axle movement.
The clutch master cylinder, slave cylinder, pipe, and hose are also part of this section, as the clutch hydraulic runs alongside the brake lines.
Dual-Circuit Hydraulic System
The dual-circuit system on USA and later Canadian cars is fundamentally more complex, with separate front and rear hydraulic circuits each served by their own servo unit. The tandem master cylinder feeds both circuits independently, so that a failure in one circuit leaves the other circuit functional. The pipe routing, adaptors, brake light switch, and servo hose arrangements are completely different from the single-circuit system. A pressure failure warning switch and corresponding dashboard warning light are fitted to dual-circuit cars.
The dual-circuit system is not interchangeable with the single-circuit system in any respect.
Pedal Box Assembly
The pedal box is common to both brake circuit types and is mounted to the bulkhead and dash panel. Seals at the bulkhead and cover plate prevent water ingress. The pedal fulcrum bolt, pedal bushes (three for manual gearbox cars, one brake, two clutch; one for automatic), rubber pedal pads, return springs, and clevis pins connecting the pedals to the master cylinder push rods are all available. The brake and clutch pedal pads have a shield-shaped pattern with vertical ribs; the automatic gearbox brake pedal uses a different, wider pattern.
Brake Fluid
Castrol Classic brake fluids are available in standard DOT 4 for normal road use, Super DOT 4 for competition and high-performance applications, and SRF high-performance motorsport specification. Silicone brake fluid (DOT 5 specification) is a non-hygroscopic alternative that does not absorb water and does not require frequent changing, a practical choice for cars that see limited annual mileage. The clutch and brake systems share the same fluid specification.