Description
Original Equipment Manufacturer (OEM) Genuine Triumph Unit-Construction 4-Speed Transmission Layshaft Third Gear.
- Part Number References: OEM 57-3890 / T3890
- Tooth Count: 22T Standard Ratio
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Extended Configuration: Matches standard 4-speed layshaft layouts spanning 1963 to 1972 model eras.
Up for sale is a genuine factory original Triumph 4-speed transmission layshaft 3rd gear replacement takeoff. Removed directly from a classic unit-construction twin engine powertrain, this is an authentic British-made high-tensile hardened steel internal gearbox component. It features a 22-tooth outer track profile and a precision machined internal splined collar to slide seamlessly along your standard transmission layshaft cluster.
Avoid cheap aftermarket reproduction transmission components that suffer from loose machining tolerances or soft steel heat-treating, which can cause rapid tooth hooking or face pitting under heavy load. This factory original hardened steel gear provides the exact structural tooth profile, pitch, and spacing required to restore crisp shifting mechanics and rock-solid gear lockup inside your transmission casing. It is an essential asset for anyone overhauling a classic dual-carb Bonneville, a single-carb Tiger, or a TR6C Trophy twin, or completing a period-correct custom bobber or chopper rebuild.
šļø Fitment & Vehicle Compatibility:
Direct factory drop-in application for standard 4-speed manual gearboxes across major Triumph 650cc unit twins and early 750cc triples:
- Triumph 650cc Twins: Fits 1963 to 1972 T120, T120R Bonneville, TR6, TR6R Tiger, and TR6C Trophy models running a standard 4-speed cluster layout.
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Triumph 750cc Triples: Fits 1968 to 1972 T150 Trident platforms utilizing standard-ratio 4-speed gearboxes.
š Condition Notes:
This is a pre-owned vintage factory transmission takeoff component.
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The Gear Teeth: All 22 individual tooth profiles are structurally sound, sharp, and true, entirely free from broken steps, heavy face pitting, or chipped engagement edges.
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Internal Bores: The internal splines and slide tracking paths are clean, sharp, and free of deep scoring or out-of-spec mechanical play.
- Cosmetics: The gear shows normal uniform mechanical polishing wear along the engagement faces, typical cosmetic vintage transmission oil discoloration, and minor superficial storage oxidation from sitting in an inventory bin (as clearly detailed in the product photos). It is fully intact and ready to clean, lube, and install into your shifting stack.
