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

A common problem on 45”/750 cc transmissions are stripped or damaged threads of the filler spout. The repair bushing allows for a professional repair without welding. The OD thread is a common M18x1.5 plug thread, the ID thread is M14x1.5. After installation you have the coice of cutting down the thread of your existent plug or purchasing the readymade M14x1.5 plug. Compared to welding this is a piece of cake.

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 and are ready for the next gear change. Thus it is possible to convert your trusty 45 cui. hand shifter Flathead to foot shift or to a Jockey shifter.
Besides the ratchet each kit comes with a bag of small parts which contains a ball joint, clevises and various mounting parts. Not included are shifter rods and shift levers.

Reproduction of the stock stud for the kickstarter spring of 45”/750 cc Sidevalves.

An essential when working on a transmission. These quality stands clamp into a vise and firmly hold the case during repair and overhaul.