| Also known as | T3890 |
| Diagram | Fig. 10 — GEARBOX SHAFTS AND GEARS · ref 7 |
| Subsystem | gearbox |
| Listed in parts books | 1970–1972 |
Layshaft third gear (22T)
Layshaft third gear (22T) for the gearbox cluster, also listed under the older T3890 number.
57-3890 is the layshaft third gear, a 22-tooth gear that lives on the layshaft inside the gearbox. It shows up in the catalog under the GEARBOX SHAFTS AND GEARS and GEARBOX INNER COVER AND SELECTORS figures, which puts it right in the middle of the gear cluster and selector mechanism rather than being some peripheral piece. The old book number for this one was T3890, so if you're working from an earlier parts list that's the number you'd see instead of 57-3890.
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Third gear on the layshaft pairs up with its mate on the mainshaft to give you that gear ratio, and the selector forks slide the appropriate gears into engagement as you work the pedal. Because this part sits inside the gearbox cluster, swapping it means the box is already apart and you're looking at shims, thrust washers, and the rest of the shaft assembly while you're in there.
Our catalog listings for this one span the early 1970s. If you're rebuilding a gearbox and pulling the layshaft out, it's worth inspecting the dogs and teeth on this gear closely since wear here shows up as trouble selecting or holding a gear.
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