| Also known as | T1478 |
| Diagram | Fig. 8 — GEARBOX SHAFTS, BEARINGS AND INNER COVER · ref 2 |
| Subsystem | gearbox |
| Listed in parts books | 1964–1970, 1974 |
OIL SEAL 500 TRI G BOX UK
Gearbox mainshaft oil seal for the unit-construction 500 twin, PN 57-1478 (T1478).
This is the oil seal off the gearbox mainshaft on the unit-construction 500 twins, sitting in the inner cover around the high gear/sprocket area per the parts book listing under GEARBOX SHAFTS, BEARINGS AND INNER COVER. It's a small, unglamorous part but it's the thing standing between your gearbox oil and the outside world at that shaft, so a tired or hardened one is a common source of a gearbox that slowly loses oil onto the primary side or the floor.
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Catalogers list this under 57-1478, with T1478 as the older-style part number stamped in earlier books - same physical seal, just the two eras of Triumph numbering. Our records show it turning up across gearbox listings from the mid-to-late 1960s.
If you're already in the inner cover for a rebuild or a shaft bearing swap, it's worth putting a fresh one of these in while everything's apart rather than closing it back up and finding out later that the old seal was the leak all along.
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