The transmission of the TD and TF comprises a single dry-plate Borg and Beck clutch, a four-speed gearbox derived from the MG Y-type, a Hardy-Spicer propshaft, and a hypoid rear axle. This is one of the most change-rich areas of the TD specification, clutch size increased at engine 9408, the operating mechanism changed from cable to rod, gearbox internals were revised at later breakpoints, and the rear axle changed from BSF to Unified at a specific chassis number. All TFs use the larger-clutch specification.
Clutch System, The 7¼" to 8" Change
The clutch changed from 7¼-inch (TD to engine 9407) to 8-inch (TD from 9408, all TFs), requiring a new flywheel casting with larger ring gear, pressure plate, driven plate, and revised bellhousing internals. The ring gear increased from 10?-inch to 10¾-inch internal diameter. A three-piece kit is available for the 8-inch specification, with individual covers, plates, flywheels, and ring gears for both. A clutch alignment tool centres the driven plate on the spigot bush before mating, forcing a misaligned gearbox risks damaging input splines and driven plate hub.
Clutch Operating Mechanism, Cable to Rod
The clutch operating mechanism changed from cable (to chassis TD/22250) to rod (from TD/22251 in November 1952), with a stop bolt added to the pedal bracket. All TFs use the rod mechanism; the two are not interchangeable. The cross shaft, bushes, fork, and operating lever also changed with the clutch upgrade, the shaft increased from ?-inch to ¾-inch with matching bushes, fork, and lever. Woodruff keys and taper pins are size-specific.
A return spring, fume-excluder rubber, and retainer complete the pedal hardware. The pedal is handed by drive side.
Gearbox
The four-speed gearbox is derived from the MG Y-type saloon, with synchromesh on second, third, and top gears only, first gear is non-synchromesh. Three specifications exist by engine number: to engine 9407 (with 7¼-inch clutch bellhousing), engine 9408 to 16481 (8-inch clutch, no selector shaft support cap), and from 16482 through all TFs (8-inch clutch, with selector shaft support cap). Reconditioned gearboxes are available on customer's own unit basis in all three specifications. The speedometer drive pinion and gear vary by rear axle ratio, distinct components are catalogued for the 5.125:1 (standard TD), 4.875:1 (optional TD, standard TF), and 4.55:1 (TD option) ratios.
A Woodruff key was added to the drive worm from engine XPAG/TD2/16978; earlier cars use the previous arrangement. The gear lever, chrome nut, retaining pin, spring, and circlip are universal. Gear knobs come in original Bakelite plus wood and leather alternatives in black and tan.
Propshaft
The Hardy-Spicer propshaft is a short single-piece unit available new or on a customer's own unit reconditioned basis. Universal joints are available in greasable and sealed types. Front yoke, flanges, flange bolts, and universal joint grease nipples are all available as individual service items.
Rear Axle, The BSF to Unified Thread Change
The rear axle changed from BSF to Unified (UNF) thread at chassis TD/12285. This affects almost every threaded component: half shafts and their nuts, axle case studs and nuts, differential cage, pinion flange nut, crown wheel bolts, wheel studs and nuts, and the axle cover studs. BSF and Unified components cannot be mixed at a threaded joint, a new half shaft supplied in Unified thread must be fitted with its matching Unified nut, and should not be used with the earlier BSF nut. Three rear axle ratios are catalogued as complete crown wheel and pinion sets: 5.125:1 (standard TD), 4.875:1 (optional TD, standard TF), and 5.444:1 (optional, shorter gearing for pulling or competition).
All three are available in both BSF and Unified thread for period-correct fitment. A fourth ratio, 4.55:1, was a factory TD option providing taller gearing, with dedicated speedometer drive components catalogued. Differential bearings, collars, thrust washers, and pinion pin are common to both thread types.
Rear Hub and Wheel Mounting
The rear hub arrangement differs between disc and wire-wheeled cars. Steel-wheeled hubs use integral drums with five studs (BSF to chassis 12284, Unified from 12285 through all TFs). Wire-wheeled cars use separate splined hubs with separate drums on drum-retaining studs and lock tabs. Spinners come in two-ear and octagonal styles in LH and RH thread by side.
A complete wire wheel conversion kit is available for both TD and TF, comprising splined hubs, drums with fixings, two-eared spinners, hammer, and spare wheel carrier adaptor with spinner.