The external gearbox section covers the gearbox assembly itself, its external fittings, the gear selection mechanism, the rear engine mounting that supports the gearbox end of the powertrain, and the speedometer drive, everything outside the gearbox casing that enables operation and mounting of the unit within the car.
Reconditioned Gearboxes
Complete reconditioned gearboxes are available on a customer's own unit basis in all three specifications: early TD to engine 9407 (7¼-inch clutch bellhousing), TD from engine 9408 to 16481 (8-inch clutch, without selector shaft support cap on remote), and TD from engine 16482 through all TFs (8-inch clutch, with selector shaft support cap on remote). The support cap on the later gearbox provides additional bearing support for the selector shaft within the remote housing, improving the precision and longevity of the gear selection mechanism. A complete gasket set is available for reassembly after any major external work, along with the oil filler and drain plugs and the dipstick.
Gear Selection Mechanism
The gear lever sits in the remote housing at the rear of the gearbox, connected to the internal selector shafts through the remote selector levers. The gear lever itself, its chrome retaining nut, retaining pins, spring, retainer, and circlip are common across all gearbox variants. The rear selector lever is located within the remote housing, operating on a ball and spring plunger arrangement that provides the detent feel when changing gear. Selector shaft balls, springs, and the plungers that govern the gate resistance are available as individual service items.
Gear Knobs
The original gear knob is available in its factory-pattern Bakelite form. Alternative finishes include a turned wooden knob, and leather-covered knobs in both black and tan. The thread that mounts the knob onto the gear lever is common to all variants, so any of the available styles will fit any gearbox.
Speedometer Drive
The speedometer drive comprises a pinion in a housing on the gearbox rear extension, driven by a gear on the mainshaft. Three pinion and gear combinations are available to match the three catalogued rear axle ratios: 5.125:1 (standard TD), 4.875:1 (optional TD, standard TF), and 4.55:1 (TD option). The correct combination must match the fitted axle ratio for an accurate speedometer reading. A Woodruff key was added to the speedometer drive worm gear on the mainshaft from engine number XPAG/TD2/16978, improving the positive drive between gear and shaft, gearboxes before this change rely on a friction fit that can slip over time. The speedometer pinion housing and its two securing screws are common across all ratios.
Reversing Light Provision
The gearbox casing includes a boss at the position for a reversing light switch. Most TD and TF cars left the factory without reversing lights fitted, and the boss is closed with a blanking plug.
For cars originally specified with reversing lights, or retrofitted with them, a reversing light switch is available to replace the blanking plug, the switch is operated by the movement of the reverse selector and closes the circuit automatically when reverse is engaged.
Rear Engine Mounting
The rear of the powertrain, the rear of the gearbox, is supported on a rear engine mounting bracket that attaches to the gearbox extension. The bracket carries a rubber mounting kit comprising a pair of mounting rubbers and a rebound rubber, with a fork that locates to a clevis pin through a cup washer. A nut and split pin retain the clevis pin. The rear mounting is common between TD and TF. Deteriorated mounting rubbers allow the rear of the gearbox to sag and drift during acceleration and deceleration, stressing the propshaft universal joints, exhaust connections, and, on severely worn mountings, the gear linkage itself.
The mounting rubbers are routine service items that should be inspected during any major transmission work.
Ordering Considerations
For reconditioned gearbox assemblies, the engine number determines the correct specification, pre-9408, 9408 to 16481, or 16482 onwards. For speedometer drive components, the rear axle ratio is the identifying factor. Most other external gearbox fittings (gear lever, selector components, remote housing fixings, gear knobs, reversing light provision) are common across all TD and TF gearboxes and do not require model-specific identification. The rear engine mounting is common to both models.