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Fixed my speedometer! It's accurate now!


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But I didn't take a single picture!:banana:

You have to take the thing ALL the way apart, there's two disks shaped like shallow cups.. one fits inside the other. The largest has what looks like a fat iron washer inside, so you have a cup with a smaller cup fitting just inside covering the fat washer attatched to the larger cup... I wish I'd taken pictures..

Anyhoo, it's a fluid coupling device (like a torque converter in an auto tranny... but air is the fluid in this case). The big cup/fat washer is never supposed to tough the small cup.. it's very close to it, but has a slight gap. When the large cup/fat washer gets spun by the speedo cable, it moves air, which moves the smaller cup (which is connected directly to the indicator needle).

The ratio of movement between the cups is directly related to the space in between them. A larger gap will result in a lower indicated speed, a tighter gap shows a higher indicated speed for the same input speed.

The gap in maintained by a needle (pilot) on the inside of the small cup that rides in a brass pilot bushing in the large cup. Lengthen the needle, increases the gap and that lowers the indicated speed...

But you can't lengthen the needle! DOH! Like I said, take the WHOLE thing apart, take the small cup with it's shaft and set it on a workbench (open end of the cup down, end of the shaft up) and tap it gently. (it's soft, thin aluminium-- tread lightly!). Reassemble and test... repeat till your indicated speed agrees with your GPS.

My speedo went wild on the way home last night, reading 120mph when I was doing 15. I had nothing to loose by taking mine apart. First try and I got an indicated 55mph with 54mph showing on the GPS. (lucky!)

I'll look around for pics of someone else taking their speedo apart, I really don't want to go into mine a second time... it's not hard to do, but it seems delicate. Not to mention the housing has to be pried apart....🙂 (barely tell once it's back together.)

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But I didn't take a single picture!:banana:

You have to take the thing ALL the way apart, there's two disks shaped like shallow cups.. one fits inside the other. The largest has what looks like a fat iron washer inside, so you have a cup with a smaller cup fitting just inside covering the fat washer attatched to the larger cup... I wish I'd taken pictures..

Anyhoo, it's a fluid coupling device (like a torque converter in an auto tranny... but air is the fluid in this case). The big cup/fat washer is never supposed to tough the small cup.. it's very close to it, but has a slight gap. When the large cup/fat washer gets spun by the speedo cable, it moves air, which moves the smaller cup (which is connected directly to the indicator needle).

The ratio of movement between the cups is directly related to the space in between them. A larger gap will result in a lower indicated speed, a tighter gap shows a higher indicated speed for the same input speed.

The gap in maintained by a needle (pilot) on the inside of the small cup that rides in a brass pilot bushing in the large cup. Lengthen the needle, increases the gap and that lowers the indicated speed...

But you can't lengthen the needle! DOH! Like I said, take the WHOLE thing apart, take the small cup with it's shaft and set it on a workbench (open end of the cup down, end of the shaft up) and tap it gently. (it's soft, thin aluminium-- tread lightly!). Reassemble and test... repeat till your indicated speed agrees with your GPS.

My speedo went wild on the way home last night, reading 120mph when I was doing 15. I had nothing to loose by taking mine apart. First try and I got an indicated 55mph with 54mph showing on the GPS. (lucky!)

I'll look around for pics of someone else taking their speedo apart, I really don't want to go into mine a second time... it's not hard to do, but it seems delicate. Not to mention the housing has to be pried apart....🙂 (barely tell once it's back together.)

In the process, did you adjust your odometer🤣

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