Speedometers and Cables

Tachometer drive parts may be found here timing chests, click here for oil pumps.

When fitting a reconditioned speedometer it is advisable to also fit a new cable as an old one may damage the new unit. The cable can be tested by holding one end of the inner cable and attempting to twist the other end, more than a ¼ to ½ a turn of movement indicates that it should be replaced.

A group speedometers were always driven from the gearbox and were initially mounted on a bracket on the forks and from 1953 in the headlamp cowl. The instruments on the sporting Road Rocket and Super Rockets were mounted a variety of brackets depending on whether 1 or 2 instruments were fitted. It would appear that there was an option to have only a rev counter fitted or a speedometer as well for 1954-57; whilst for 1958-62 either or both could be fitted. From 1960 the Super Rocket was supplied with either the cowl, with speedometer in it or with headlamp ears and the clock(s) on brackets. The rev counter was driven from the magneto until 1960 when the drive was taken from the oil pump instead.

B group Speedos were mounted on a fork top bracket before the war and driven from the front wheel. With the introduction of telescopic fork models the speedometer moved initially to the petrol tank until 1948 when it moved to the forks. Drive on telescopic models was from the gearbox.

C group speedometers were initially driven from the front wheel and mounted on top of the forks. With the advent of the telescopic forks the drive moved to the rear wheel and the speedometer head moved to the tank. When the 4 speed gearboxes were introduced in 1951 the speedometer was driven from the gearbox and the speedometer was on the forks.  In July 1954 the speedometer on 3 speed gearbox equipped machines moved to the forks but the drive remained at the rear wheel. The C10L used a ‘D’ shaped speedometer.

M group girder fork speedometers were driven from the front wheel but telescopic fork model’s drive came from the gearbox. The speedometer was always on the forks mounted on a bracket either to the side or centrally.