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5-Speed Transmission Case for 1965–'85 4-Speed Big Twins

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Product Reviews

S&S 4 to 5-speed transmission cases are designed to convert 4-speed big twin frames with 1965–'85 shovelhead style drivelines and chain final drives to 5-speed transmission (see notes below). Includes the shift lever adjustment screw, shifter shaft guide, and all studs and dowel pins required for assembly. Studs and dowel pins are installed. Accepts most OEM and aftermarket 5-speed style trap doors, bearings, seals, and other parts designed for 1985–'99 big twin 5-speed transmissions. The OEM trap door will require minor modification for use with this case. All modifications are explained in the instructions. Main and counter shaft bearings and seals are not included.

Features and Benefits:

  • Update 4-speed bikes to 5-speed transmission
  • CNC machined from 356-T6 aluminum castings
  • Accepts most OEM and aftermarket parts designed for 1985–'99 big twin 5-speed transmissions

Kit contains: transmission case assembly, required hardware, and instructions.

Items available for purchase separately:

NOTESThe S&S 4 to 5-speed transmission case is not compatible with the factory Harley-Davidson® primary belt drive used on 1980–'83 FXSB Sturgis models.
For applications that utilize an existing 4-speed driveline, a 1980 to early '84, 5-speed style chain-drive mainshaft and 1980 to early '84 style main drive gear must be used.
These parts are compatible with the tapered I.D. clutch hub used on 4-speed big twins.
4 and 5-speed transmissions utilize the same 1:1 final drive ratio. As a result, the 5-speed gear set will not alter engine RPM at highway speeds. The additional gear narrows the gap between lower gears for improved acceleration and better performance in traffic.
This transmission case will fit earlier big twin frames. However, the engine sprocket shaft must be of the type used in 1970–later big twin style engines. The transmission case itself is compatible with H-D® secondary (rear) belt drive if the correct mainshaft, main drive gear, inner primary cover, starter shaft, starter housing, and related parts are used. However, the builder may encounter other obstacles when converting a motorcycle with chain final drive to belt final drive.
The purchaser's countershaft and shift fork shaft will require shortening.
A low contact-style countershaft gear must be used in this transmission case to match the 1980–'84 main drive gear required. Harley-Davidson® replaced low-contact gears with high-contact gears on 1994 international big twin models and 1995 U.S. models.
Low and high contact gears may not be mixed.
S&S trap doors are of the 1987–'99 style. S&S recommends using this style trap door and end cover with the "ball and ramp" clutch actuator. The strength of the earlier, lever-type actuator is marginal for heavy clutch springs sometimes required in high performance applications.
Most 4-speed big twin style engines utilize transmission-driven mechanical vspeedometers. This transmission case has no provision for speedometer drive, and must be used with a wheel-driven speedometer and speedometer drive. The existing wheel may require modification to accept the speedometer drive unit.
The clutch-actuator end of the 4-speed clutch cable is not compatible with the 5-speed type clutch actuator. Options are to replace the existing clutch lever with an 1987–'99 style lever or purchase a custom cable with the correct ends from Barnett Tool and Engineering in Ventura, California. (Phone: 805-642-9435)

best method to increase speed of the bike in low cost:)
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