Internal gearbox components are the parts within the gearbox casing that require the gearbox to be dismantled for replacement. These include the synchro rings, laygear and layshaft, selector forks, and the input and output shaft bearings.
Gearbox
For the 1275cc BMC A-Series gearbox, three synchro rings are fitted (for second, third, and fourth gears, first gear is non-synchromesh and uses straight-cut gears). The laygear runs on a layshaft with needle roller bearings, and the selector forks engage with the synchro hubs to select each gear. A complete gearbox rebuild kit containing all bearings, synchro rings, gaskets, oil seals, and small parts is available. For a gearbox that crunches on one particular gear, the synchro ring for that gear can often be replaced without a complete rebuild, though inspecting the other synchros while the box is apart is strongly recommended.
Gearbox (1500)
For the 1500 Triumph gearbox, four synchro rings are fitted (all gears including first, which is fully synchromesh, unlike the A-Series). The laygear was revised during production, with an improved design from gearbox number 241364 onward.
The first motion shaft also exists in two variants with different bearing arrangements. A complete rebuild kit specific to the 1500 gearbox is available.
Gear Lever
The gear lever anti-rattle mechanism on the 1275cc (the "zizzle kit") sits within the remote housing on top of the gearbox and can be renewed from inside the car without removing the gearbox. This is a common maintenance item, worn anti-rattle components cause a buzzing vibration through the gear lever that is particularly noticeable at cruising speed.