The rear brake specification on the MGA depends on the variant. Pushrod 1500, 1600 and 1600 Mk II cars all use 10-inch Lockheed rear drum brakes, with the same drum dimensions and the same general architecture across the three pushrod variants, a single wheel cylinder per drum operating one leading and one trailing shoe. Twin Cam and De Luxe cars use 11-inch Dunlop rear disc brakes instead, with special pad carriers for handbrake operation. This section covers rear brake components across both systems.
Pushrod 1500, 1600 and 1600 Mk II, 10-inch rear drums
Pushrod cars use Lockheed 10-inch rear drum brakes, 1¾ inches wide, painted black. Each rear drum has a single wheel cylinder operating one leading and one trailing shoe.
Original lining specification on the 1500 is Ferodo DM13, size 9.6 x 1.75 inches, with total rear lining area of 67.2 square inches. The 1600 and 1600 Mk II carry over the same drum dimensions but use later DON24 linings, size 9.63 x 1.7 inches, a small change to the liner but mechanically the same rear brake arrangement. Several rear-brake production changes affect ordering on the 1500. The banjo connection to the rear wheel brake cylinders was changed from a straight to a right-angle type at car/chassis 22741.
The three-way connection and brake pipes to the rear brakes were modified to standardised UNF threads at car/chassis 27989 (disc-wheeled cars) and 28540 (wire-wheeled cars), wire-wheeled cars received the UNF change a little later than disc-wheeled cars. The pushrod rear drum itself is different between disc-wheeled and wire-wheeled cars, because the drum-and-hub combination differs: on disc-wheeled cars the drum bolts to a four-stud hub; on wire-wheeled cars the drum fits over a splined centre-lock hub, and the assembly is not interchangeable between the two.
Rear brake service hardware
The rear drum brake shares a common set of service items across the pushrod range: shoe return springs, shoe retaining cups and springs, the wheel cylinder and its dust boots, shoe-adjuster hardware, drum-retaining countersunk screws, wheel cylinder bleed nipples and protective plugs, and the various nuts, locktabs and fittings that secure the assembly. MGOC Spares stocks Girling shoe horn tools for drum-brake work alongside the service parts themselves; the shoe horn is a hand tool that lifts the shoes over the retaining cups for service without distorting the shoe ends. Flexible brake hose clamps are stocked for use during hose replacement and for temporary line-isolation during bleeding work.
Twin Cam and De Luxe, 11-inch Dunlop rear disc
Twin Cam and De Luxe cars use 11-inch Dunlop rear disc brakes, the only MGA variants with rear discs. The rear disc calipers were modified at approximately car/chassis 836 along with the front units. The rear caliper carries special pad carriers for the handbrake to operate against, an arrangement the Identification Guide describes as "not terribly effective and troublesome to set up", and a well-known characteristic of the Twin Cam and De Luxe. Factory-recommended fluid is Wakefield Crimson (later Dunlop disc brake fluid) or any brake fluid to specification SAE70.R1 or SAE70.R3.
The De Luxe uses a slightly modified Twin Cam master cylinder, with a factory service kit available to convert a Twin Cam master cylinder to the later De Luxe specification.
Ordering considerations
Rear brake part selection starts with the variant, pushrod or Twin Cam / De Luxe, and then, for pushrod cars, with the wheel type (disc or wire), which affects the drum and hub specification. Chassis-number breakpoints to confirm on pushrod 1500s: 22741 (banjo connection at wheel cylinders), 27989 (disc-wheeled UNF changeover), 28540 (wire-wheeled UNF changeover). Twin Cam / De Luxe rear disc caliper specification depends on whether the car is before or after Twin Cam chassis 836. Providing the chassis number, variant and wheel type at point of ordering is the starting point for accurate rear brake parts selection.