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4-Speed Conversion Kit 45”/750cc

A drawback with original 3-speed transmissions is the large gear ratio difference between 1st and 2nd, i.e. from 2.47 to 1.57:1 with a consequent big rpm drop. If you ever rode 2-up in the mountains you will know how annoying this can be. With the installation of this 4-speed conversion kit one can achieve a big improvement here because its extra gear allows you to stay in the power band much better for an overall riding performance unknown before. Additionally, all gears are machined from modern materials for higher strength and feature an updated tooth-design for smoother and quieter running. Solo machines, sidecar rigs and Servi-cars - all likewise benefit from these features.

The conversion kit includes all gears and the shifter drum to transform an old 45” gear box into a 4-speed transmission. All other stock 3-speed parts, like shafts, shifter forks, etc. can be retained or must be purchsed separately if not present. The original primary drive with clutch and the chain sprocket with cover fit without problems. After installation the 4-speed tranny will look exactly the same as its 3-speed counterpart so nobody can tell the difference from its outer appearance. The only extra part required is a 4-speed shifter gate. The stock side cover has to be machined for clearance. As an option a pre-machined version is also available.

Stock 3-speed gear ratios:

1st - 2.47:1

2nd - 1.57:1

3rd- 1:1

4-speed gear ratios:

1st - 2.67:1

2nd - 2.03:1

3rd - 1.42:1

4th - 1:1

... more
This conversion kit should be installed in a professional workshop by an experienced mechanic.
Conversion kit »4-Speed« by Samwel Supplies; fits 45 cui./750 cc models 1941-1973; Europe
W&W# Picture net price* Available from warehouse Germany?
74-066 4-Speed Conversion Kit 45”/750cc $853.18 kit
in stock
* United States of America: Tax free shipping. Please check your local import fees.


  • 74-005

    74-005 Side cover; fits 45”/750cc Flatheads 1941-1963; 3-speed and 4-speed; cast iron; replaces OEM 34821-41; gross weight: 1.22 kg

  • 45-852

    45-852 Shifter guide; fits Big Twin 1947-1965; 4 speed; steel, chrome-plated; replaces OEM 33789-47; gross weight: 190 g

  • 45-854

    45-854 Shifter guide; fits Big Twin 1937-1938 and 1940-1946; 4 speed; steel, chrome-plated; replaces OEM 2209-37, and 33789-37; gross weight: 160 g

  • 59-090

    59-090 Gasket kit by James Gaskets; for Transmission; fits 45 cui/750cc 1941-1973; replaces OEM 33030-41; gross weight: 130 g

  • Transmission Case and Related Parts

    Transmission Case and Related Parts

See also:

  • HMB Shifter Ratchet for 750cc/45cui

    HMB Shifter Ratchet for 750cc/45cui This shifter mechanism basically works like a Ratchet Top of Big-Twin models: after each shifting operation all involved levers return to their home position ...

  • 4-speed Transmission 45”/750cc

    4-speed Transmission 45”/750cc Fully assembled, ready-to-install, 4-speed (!) transmissions for 1941-up 45 cui./750 cc Sidevalve Harleys. It is a fact that while the engines seem to last ...

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