| Also known as | T1179 |
| Diagram | Fig. 8 — GEARBOX SHAFTS AND GEARS · ref 5 |
| Subsystem | gearbox |
| Listed in parts books | 1960–1962, 1967–1968, 1970 |
Mainshaft third gear (23T)
Mainshaft third gear (23 tooth) for the gearbox, part 57-1179, also known by its earlier T1179 designation.
57-1179 is a mainshaft third gear with 23 teeth, listed in the gearbox shafts and gears section of the parts book. It rides on the mainshaft inside the gearbox and works with its matching layshaft gear to give you third gear ratio when the selector engages it. If your book was printed before the numbering changed, you may find this same part listed as T1179 - same physical gear.
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The catalog record ties this to gearbox rebuilds spanning 1960 through 1970, appearing across six catalog listings over that stretch. Because there are different gear clusters used across those years, check tooth count and shaft fit against what's already in your case before you swap it in.
If you're rebuilding the box anyway, it's worth inspecting the dogs and bore on the old gear at the same time you're in there, since wear here is usually what sends people looking for a replacement in the first place.
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