Description
Original Equipment Manufacturer (OEM) Genuine Triumph Unit-Construction 4-Speed Transmission Mainshaft Third Gear.
- Part Number References: OEM #57-3889 / T3889 [INDEX]
- Tooth Count: 23T Standard Ratio [INDEX]
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Extended Configuration: Matches standard 4-speed mainshaft layouts spanning late-1960s to mid-1970s [INDEX, INDEX].
Up for sale is a genuine factory original Triumph 4-speed transmission mainshaft 3rd gear replacement takeoff [INDEX, INDEX]. Removed directly from a classic unit-construction engine powertrain, this is an authentic British-made high-tensile hardened steel internal gearbox component [INDEX, INDEX]. It features a 23-tooth outer track profile and a machined interior race path to slide seamlessly along your standard transmission mainshaft cluster [INDEX].
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 [INDEX]. It is an essential asset for anyone overhauling a classic dual-carb Bonneville, a single-carb Tiger, or a T150 Trident triple, or completing a period-correct custom bobber or chopper rebuild [INDEX, INDEX].
šļø Fitment & Vehicle Compatibility:
Direct factory drop-in application for standard 4-speed manual gearboxes across major Triumph unit twins and early triples [INDEX, INDEX]:
- Triumph 650cc Twins: Fits 1969 to 1972 T120, T120R Bonneville, TR6, TR6R Tiger, and TR6C Trophy models [INDEX, INDEX].
- Triumph 750cc Triples: Fits 1970 to 1972 T150 Trident platforms running standard-ratio 4-speed gearboxes [INDEX].
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(Interchange Note: Mechanically compatible and crosses over directly with early part numbers 57-2378and 57-1179) [INDEX].
š Condition Notes:
This is a pre-owned vintage factory transmission takeoff component [INDEX].
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The Gear Teeth: All 23 individual tooth profiles are structurally sound, sharp, and true, entirely free from broken steps, heavy face pitting, or chipped engagement edges [INDEX].
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Internal Bores: The internal slide tracking collar surface is smooth, clean, and free of deep scoring or out-of-spec mechanical slop [INDEX].
- Cosmetics: The gear shows normal uniform mechanical polishing wear, typical cosmetic vintage transmission oil discoloration, and minor superficial storage oxidation from sitting in an inventory bin (as clearly detailed in the product photos) [INDEX]. It is fully intact and ready to clean, lube, and install into your shifting stack [
