TriVelox's first design was an entertainingly brutal, deliciously steampunk, device.

The chainline remains straight in all gears, so the gear is changed by moving the sprocket cluster sideways. The sprocket cluster slides on a set of splines on the outside of the tubular body that contains the freewheel ratchet.

The gear change mechanism is a shaped plate that sits between two of the sprockets. The gear lever pulls a cable, and this cable then pulls the shaped plate sideways. You can see some explanation of all this in this TriVelox brochure.

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This is a very well used example - see the wear on the curved surface of the pusher plate. Its features include:

• It has a fairly long cable adjuster.
• The main arm is reasonably poorly finished with sharp edges.

Note that the TriVelox brochure states that the force to change to low gears comes from the two telescopic springs surrounding the sliding rods. Both of the derailleurs that I have also have a conventional, and rather more purposeful, helical spring around the cable.

This example also shows a vulnerability of the design. The front tube, containing the sliding rod from the pusher plate, does not look original. One might reasonably guess that the original has been destroyed. The cable adjuster is also artistically bent. Both of these features point to the fact that the mechanism has received a severe blow from the front. The design does have fragile elements that are very vulnerable to this kind of accidental damage.

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• Derailleur brands: TriVelox
• Country: UK
• Date of introduction: 1934?
• Date of this example: unknown, serial number is L373
• Model no.: unknown
• Weight: 436g excluding chain tensioning spring
• Maximum cog: 26 teeth? - this is the biggest sprocket offered by TriVelox
• Total capacity: 24 teeth? - a guess based on the range offered by TriVelox
• Pulley centre to centre: 78mm
• Index compatibility: friction
• Chain width: 1/8"
• Logic: low normal
• B pivot: none
• P pivot: sprung
• Materials: steel

Ref. 1804