Repairing Jaeger and Smiths Speedometers

An Article by Anthony Rhodes Copyright 2000

Page 9

Odometer: Mechanism

The "old" style odometers work by friction trying to turn all the odometer wheels and then a restraining clip underneath the wheel prevents motion except at certain times. The drive gear is keyed to the shaft and there are keyed washers between each of the wheels. The wheels themselves are not keyed and can turn freely. As the drive gear turns, it turns the shaft. The shaft turns the washers between the wheels. By friction, the wheels try to turn, but the clips prevent turning. The restraining clips underlie two adjacent wheels, so one wheel can disengage the clip under the next wheel to the left. The left and right edge of each wheel have a thin metal edge with notches. These notches engage the clips. On the right side of each wheel the edge has ten notches. The left side of each wheel has one notch. When looking at two wheels, as the right wheel turns one entire revolution, it disengages the clip under the left wheel once. The right wheel moves ahead by one notch, then the clip re-engages and prevents further forward motion until again disengaged.

The "intermediate" and "new" main and trip odometers function similarly. The "new" type has a different layout for the drive gear, but the odometer wheels function similarly. The drive gear spins the shaft, then the shaft turns the 1/10ths wheel. The main odometer has a 1/10ths wheel that is fairly narrow and has no lettering. The odometer wheels turn freely on the shaft and are indexed by a cog between adjacent wheels. The main odometer has the cog between the wheels so there is no gap between the wheels. The trip odometer has more widely spaced wheels and the cogs are external to the wheels. These odometers turn much more freely than the "old" types as they do not rely on friction to make any movement.

Figure 6: Diagram of "old style" main odometer components.
Figure 7: Diagram of "intermediate style" odometer components.
Figure 8: Diagram of "new style" odometer components.

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