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TR2/3/3A Speedometer Bounce with Odometer Gear Movement - Benchtop Calibration

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Joel M

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Is it normal for there to be some amount of bounce in a Jaeger speedometer needle that coincides with the ratcheting of the two brass odometer gears? During repair I did a benchtop confirmation with the odometers NOT installed, using a DC motor and controller set to the calibration value printed on the face. It was perfect 60 mph with no bounce. I then installed both odometers for reconfirmation, but now the speedometer bounces about 1 mph every time one of the odometer brass gears is ratcheted. I tried two different cables and also direct drive without a cable, but the result is the same. Any ideas?

Joel
1959 TR3A TS57134
 
Bouncing along at 60 I would never notice 1mph. I’ll make a note to check next time I get the TR out though.
 
Does it float or bounce? A clear bounce is usually the cable. I have tried a few and many of them float a little the faster they go. I always figured it was the magnet or something. I do have a rock solid one now and what helped with that was a nos cable, but could be luck also. I never connected the bounce to odomitor, but yeh why not--- the movement must cause something
 
Yes - as you observed, the odo number drums offer some resistance whenever the pawl advances it. From long highway trips in my TR4 in college, I could watch the speedo needle 'bump' every time the trip 10ths advanced, about 3 times in a mile. This action can cause the cable to 'slow' a bit from the resistance of advancing the odo number wheels, and then 'unwind'/speed up as the pawl lifts off the drive wheel.

Since there are separate mechanisms for trip and total miles the bump can be worse when both advance, especially if it is turning 100s or 1000s. There is an in-depth guide by Anthony Rhodes you find on the web for details.

The number wheels advance through friction between them, using thin brass wafers with springs to press them together. As they age and get dirty, I expect the friction is enough to make the bump noticeable. Maybe its unavoidable. The drums/wafers/springs can all be pulled off their shafts, cleaned, lightly lubed and reassembled but there's a lot of small parts. If you like repairing clocks or building ships in a bottle, you'll love it. Anthony devotes about 5 pages on the how to. I doubt if you could improve on your 1 MPH though!

Jeff
 
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