Description
Original Equipment Manufacturer (OEM) Genuine Triumph 650cc Unit-Construction 4-Speed Transmission Layshaft with 1st Gear Assembly.
- Part Number References: OEM #57-3864 / #57-4155 / T3864 [INDEX, INDEX]
-
Configuration: Complete 4-speed manual gearbox layshaft featuring the integrated factory-machined 1st gear cluster [INDEX].
Up for sale is a genuine factory original Triumph 4-speed transmission countershaft/layshaft takeoff [INDEX, INDEX]. Removed directly from a classic 650cc unit-construction twin engine powertrain, this is an authentic British-made high-tensile hardened steel internal gearbox component [INDEX, INDEX]. It features the classic multi-slot long spline tracking channels and the integrated low-gear face profile [INDEX].
Avoid cheap aftermarket reproduction transmission components that suffer from loose spline machining tolerances or soft steel heat-treating, which can cause the internal splines to spin or lead to rapid gear tooth shearing under load. This factory original hardened steel piece provides the exact structural spacing, gear face pitch, and shaft-to-shaft parallelism required to restore crisp shifting mechanics and rock-solid gear lockup inside your transmission casing. It is an essential mechanical asset for anyone overhauling a classic dual-carb Bonneville or single-carb Tiger project, completing a period-correct custom bobber build, or restoring a vintage 4-speed unit-twin gearbox assembly [INDEX, INDEX].
šļø Fitment & Vehicle Compatibility:
Direct factory drop-in application for standard 4-speed manual transmission gearboxes across 650cc unit-construction Triumph twins [INDEX, INDEX]:
-
Triumph 650cc Series: Fits classic 1963 to 1972 T120 Bonneville, T120R, TR6 Tiger, TR6R, and TR6C Trophy models running a standard factory 4-speed cluster layout [INDEX, INDEX]. (Always cross-reference your specific parts book and determine if your casing requires the early stepped shoulder or the later non-stepped spindle profile before purchasing).
š Condition Notes:
This is a pre-owned vintage factory transmission takeoff component.
-
The Gear Teeth: All individual 1st gear teeth profiles are structurally sound, sharp, and true, entirely free from broken steps, heavy face pitting, or chipped engagement edges [INDEX].
-
The Splines & Shaft: The long slider tracking splines are clean, deep, and free of step-wear tracking groves or twist deformation. The main bearing journal surfaces are smooth and free of severe scoring.
-
Cosmetics: The assembly shows normal uniform mechanical polishing wear, typical cosmetic vintage transmission oil discoloration, and minor surface storage oxidation from sitting in an inventory bin (as clearly detailed in the product photos), but it is fully intact and ready to clean, lube, and install into your shifting stack.
