Speedometer/tachometer "jiggle" information

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Speedometer/tachometer "jiggle" information

Postby burkbuilds » Wed Apr 02, 2014 7:01 pm

Hi, it's been a while since I've posted anything. I'm not sure exactly where this should fit but I put it here.
Over the years I've often wondered what caused some speedo's and tach's to "jiggle" instead of run steady like they always do in a car for instance. I've finally learned at least one answer to the question so I thought I'd share it.

The cable which runs from the speedo or tach is not technically a cable, it's a shaft, a flexible drive shaft to be specific and the company I now work for once supplied about all the OEM speedo "cables" to the big three automakers. The difference in a shaft and a cable is this, a cable has all the wires wrapped in the same direction around a central core wire or sometimes a rope, depending on the application. A flexible drive shaft is wound with every other layer going in the opposite direction of the previous layer and, at least at our company, it's always wound over a central wire. Really well made flexible cable will not give you much vibration in the needle of the speedo or tach. If the cable is not held to fairly close specifications during the winding process, you will get vibration, and the needle will shake. We still make some of these shafts for speedometer use but most speedo's and tach's in automobiles today are electronic and don't have a flex shaft turning between the gage and a gear or sprocket but most if not all motorcycles still use the flex shaft for that purpose. Like many things made today, price is the top priority for manufacturer's and a lot of this stuff for speedo's and things is made overseas and not held to very high quality control, so your speedo and tach needles jiggle.

Well, that may not actually help anybody, but maybe it will at least answer the question of why we have those shaky needles.

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Re: Speedometer/tachometer "jiggle" information

Postby GeorgiaRider » Fri Apr 04, 2014 6:13 am

Always enjoy more information about our bikes...
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Re: Speedometer/tachometer "jiggle" information

Postby Triangles » Fri Apr 04, 2014 6:56 am

Interesting. When I pulled mine out to clean/lube it I thought it looked almost like a tightly wound spring. My needle doesn't bounce but if it did, I would have assumed the needle bounce was caused by the cable(shaft) slightly binding due to inadequate lubrication. Thanks for the insight.

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Joined: Thu Jan 14, 2010 9:29 pm
Location: Rome, Georgia

Re: Speedometer/tachometer "jiggle" information

Postby burkbuilds » Fri Apr 04, 2014 8:09 pm

Certainly friction can add to or create a problem there but if the cable is not well made then there's not anything you could do that would make the vibration go away.

As I stated before, I don't know anyone else's process, but we heat treat every shaft as it comes off the winding heads to relieve stress and make it more flexible and to make it roll more easily. You can actually feel a lot of difference in how easily you can roll the shaft while it is being flexed in a U shape between a piece that is heat treated and one that is not. If you lay it out on the floor and roll it, a well made shaft will stay flat and roll evenly on the floor, one that is not so well made will roll and the ends or middle will ride up and it won't stay straight.

Back in the day, the company I work for made and supplied all the OEM cable in house but they couldn't keep up with the demand for aftermarket, so they imported all the stuff that went to the aftermarket suppliers. The workers who were around back then told me there was a lot of difference in the product they imported, that it was obviously inferior and that the OEM manufacturer's would not accept any shaft material that made their speedo's wobble or jiggle, so we made all that here in the good old USA.

Today our products go into things like Dremel tools, lawn equipment (think weedeaters) and medical devices (surgery stuff) but our biggest sellers are automotive sunroof cables and power seat shafts. We even made the flex shaft that operates the digging arm on the Mars Rover, which I think is pretty cool. We also make flex shafts to operate the windshield wipers on some military helicopters. There is still one production line that runs speedometer shaft but 20 years ago there were 15 lines running 3 shifts 7 days per week making nothing but speedo shafts.

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