| Diagram | Fig. 11 — GEARBOX SHAFTS AND GEARS · ref 4 |
| Subsystem | gearbox |
| Listed in parts books | 1974, 1978–1980, 1983, 1985 |
Mainshaft High Gear Assembly
Mainshaft high gear assembly for the gearbox, catalog number 57-4779, later superseded by 57-4781.
This is the mainshaft high gear assembly, part number 57-4779, and it lives in the gearbox on the mainshaft where it meshes with the layshaft to give top gear drive. It's a Triumph part, and the catalog places it squarely in the gearbox shafts and gears section.
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This part was superseded by 57-4781 at the factory, so if you're working from a later parts book you may see it listed under that number instead — same physical assembly, just a newer catalog number. If you're pulling apart a gearbox and this part looks worn on the engagement dogs or the bearing surface, it's worth checking against the mainshaft and layshaft together rather than swapping it in isolation.
Our catalog record ties this to appearances spanning 1974 through 1985, so it's associated with that later run of gearboxes rather than the earlier pre-unit or early unit boxes. Confirm fitment against your gearbox casing and shaft dimensions before ordering.
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