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Amazingly detailed info, Bill. Thanks for explaining a ubiquitous issue with the earlier P6 models. <br><br><br><div class="yahoo-signature"><a style="font-size:12px" href="https://aolapp.onelink.me/eG2g?pid=NativePlacement&c=US_Acquisition_YMktg_320_EmailSignature_AttributionDL&af_sub1=Acquisition&af_sub2=US_YMktg&af_sub3=&af_sub4=100002473&af_sub5=SentFromNewAOLApp__Interstitial_&af_ios_store_cpp=ce85ce34-ad0f-4811-a92b-a172743b064e&af_android_url=https%3A%2F%2Fplay.google.com%2Fstore%2Fapps%2Fdetails%3Fid%3Dcom.aol.mobile.aolapp%26listing%3Demail_signature_attribution">Sent from the all new AOL app for iOS</a><br></div><br><p class="yahoo-quoted-begin" style="font-size: 15px; color: rgb(132, 115, 255); padding-top: 15px; margin-top: 0px;">On Tuesday, August 19, 2025, 1:49 PM, magnet--- via Rovernet <rovernet@rovernet.org> wrote:</p><blockquote class="iosymail"><div dir="ltr">Hi Larry,<br clear="none"><br clear="none">Speedo issues almost always come down to lubrication, or to be more <br clear="none">precise the lack of it.<br clear="none"><br clear="none">As has been pointed out, the lube in the cable, and if present, in the <br clear="none">right-angle drive behind the speedo head, dries out and gets gummy. <br clear="none">Anything that resists the even turning of the cable, especially up near <br clear="none">the head, can cause jitter, as the cable "winds up" and then "lets go" <br clear="none">once it overcomes the resistance. On the "let go" phase, the cable <br clear="none">momentarily gives a little surge, resulting in a spike in the speedo <br clear="none">reading.<br clear="none"><br clear="none">But a more insidious problem inside the speedo head itself often causes <br clear="none">this surging, and lubricating the cable alone will not eliminate it. <br clear="none">Smiths (aka British Jaeger) speedometers use a little pawl-and-ratchet <br clear="none">arrangement to drive the mileage counter. A worm on the speedo input <br clear="none">shaft turns a pinion gear, and this gear moves a pawl back and forth <br clear="none">every time it goes around. The pawl, in turn, pushes a toothed wheel <br clear="none">around a few degrees on each stroke, and this wheel is coupled to the <br clear="none">tenths-of-a-mile dial of the mileage counter.<br clear="none"><br clear="none">Now what happens when the lubricant of the pawl and the toothed wheel it <br clear="none">drives dries out?<br clear="none"><br clear="none">The wheel gets harder for the pawl to turn. The pawl thus has to work <br clear="none">harder on the forward stroke as it turns the wheel. This causes a <br clear="none">heavier load on the speedo cable, which winds up a bit. But the pawl's <br clear="none">return stroke is easier, and the cable unwinds, giving a flip to the <br clear="none">speedo needle. Depending on your speed, this oscillation takes place a <br clear="none">couple of times each second or faster, resulting in a small but <br clear="none">noticeable jitter in the speedo needle. At some speed, this jitter <br clear="none">coincides with the resonant frequency of the needle and hairspring <br clear="none">assembly and you get a really big swing on the needle.<br clear="none"><br clear="none">But wait, it gets even more interesting! Every time the tenths dial <br clear="none">goes through a revolution, it moves the mile wheel forward by 1. So the <br clear="none">pawl has to work even harder to turn two dials, wnding up the cable even <br clear="none">more, and causing a bigger flip when it relaxes. So once every mile, <br clear="none">you'll get a bigger swing of the needle. And every ten miles, an even <br clear="none">bigger swing, etc.<br clear="none"><br clear="none">Lubricating the pawl is easy, once you have opened up the speedo head, <br clear="none">and greasing the pinion wheel shaft is pretty straightforward too. In <br clear="none">my case, binding of this shaft was the main culprit. Just as well, as <br clear="none">lubrication of the six-wheel dial assembly would have involved more <br clear="none">disassembly than I was prepared to undertake.<br clear="none"><br clear="none">Cheers,<br clear="none"><br clear="none"> -- Bill Daddis<br clear="none"><br clear="none"><div class="yqt3488228430" id="yqtfd53767"><br clear="none">On 19-Aug-2025 8:31 a.m., larry williamson via Rovernet wrote:<br clear="none">> My speedo is steady sometimes and sometimes jumps around. What is the <br clear="none">> reason and how to fix? I can't seem to find out in the classic forum <br clear="none">> these notes. Larry<br clear="none">><br clear="none">> _______________________________________________<br clear="none">> Rovernet mailing list<br clear="none">> <a shape="rect" ymailto="mailto:Rovernet@rovernet.org" href="mailto:Rovernet@rovernet.org">Rovernet@rovernet.org</a><br clear="none">> <a shape="rect" href="http://rovernet.org/mailman/listinfo/rovernet_rovernet.org" target="_blank">http://rovernet.org/mailman/listinfo/rovernet_rovernet.org</a><br clear="none"><br clear="none"></div></div>_______________________________________________<br>Rovernet mailing list<br><a ymailto="mailto:Rovernet@rovernet.org" href="mailto:Rovernet@rovernet.org">Rovernet@rovernet.org</a><br><a href="http://rovernet.org/mailman/listinfo/rovernet_rovernet.org" target="_blank">http://rovernet.org/mailman/listinfo/rovernet_rovernet.org</a><br><blockquote></blockquote></blockquote>
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