| Also known as | T3978 |
| Diagram | Fig. 11 — GEARBOX INNER COVER AND SELECTORS · ref 20 |
| Subsystem | gearbox |
| Listed in parts books | 1969–1970, 1973–1974, 1976–1980, 1983, 1985 |
ALUMINIUM WASHER, GEARBOX INDEX PLUNGER HOUSING
Aluminium crush washer fitted under the gearbox index plunger housing to seal the joint and protect the cover boss.
This is the aluminium crush washer that seats under the gearbox index plunger housing, the small boss on the inner cover that holds the plunger locating the camplate in each gear position. It's a simple washer, but it does real work: it keeps the housing from biting into the cast boss when you tighten it down, and it helps make a seal at that joint so oil stays where it belongs.
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Catalog records show this one under 57-3978, with the older T3978 form still printed in some parts books. It turns up across gearbox inner cover and selector mechanism figures from 1969 into 1985, so it's a long-running fitment across that gearbox family.
Because it's a crush washer, treat it as a one-time-use item. Any time you pull the index plunger housing off for service, put in a fresh one rather than reusing the old washer.
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