AntonyH Posted March 30, 2016 Share Posted March 30, 2016 My speedo is still dicky... after many years of being rock solid, the needle recently started occasionally bouncing up to the 80mph mark, when actually travelling at, well, any speed really. Even, sometimes, when parked with the engine running.The speedo sensor is in the bottom of the gearbox (K-series, 6-speed) not at the wheel.On the advice of our local 7-friendly garage I replaced the quill as a first attempt and that made mostly no difference, other than occasionally now the speedo doesn't read at all. Hmm.I'm guessing the problem is the sensor unit as a whole, or maybe the cables to it.Question: How does the sensor work, in an electrical sense? Does the turning of the quill generate a voltage, or does it adjust an impedance?Just trying to figure out how to trace the problem so I don't buy a replacement unnecessarily if the problem is elsewhere in the loom (or is the dial itself). Link to comment Share on other sites More sharing options...
AntonyH Posted March 30, 2016 Author Share Posted March 30, 2016 Adding comment to enable notifications... Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted March 30, 2016 Member Share Posted March 30, 2016 I've always assumed it was a rotary pulse generator, as on rear wheels and bikes. Replacement options. Check the feed and earth directly, and continuity on the signal return.JonathanPS: Does anyone know if there's a clearance adjustment on these? Link to comment Share on other sites More sharing options...
AntonyH Posted March 30, 2016 Author Share Posted March 30, 2016 Thanks.There is definitely no clearance adjustment on the sensor, it just screws on to the part that's captive in the gearbox. The sensor itself is sealed. Link to comment Share on other sites More sharing options...
OliverSedlacek Posted March 31, 2016 Share Posted March 31, 2016 I would guess that the sensor is a hall sensor. If so, it detects the presence of a magnetic field and generates an electrical pulse for every magnetic pole that passes under the sensor. Link to comment Share on other sites More sharing options...
AntonyH Posted April 18, 2016 Author Share Posted April 18, 2016 Seemingly now sorted, update in previous thread:http://www.lotus7.club/comment/2178257#comment-2178257 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted April 18, 2016 Member Share Posted April 18, 2016 That sounds right.Well done.Jonathan Link to comment Share on other sites More sharing options...
AntonyH Posted April 19, 2016 Author Share Posted April 19, 2016 Just as well really, if that had made no difference I'd have been spending £70 on a speedo sensor that may or may not have made a difference! Link to comment Share on other sites More sharing options...
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