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Speedo/tach not accurate

Discussion in 'XJ Technical Chat' started by Haapala, May 23, 2015.

  1. Haapala

    Haapala Member

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    My speedometer on my 750 Seca lags behind about 10 mph from how fast I'm actually going, and my tachometer seems slow to respond/bounces around a bit at a constant speed. Would lubing the cables fix this?
     
    Haapala, May 23, 2015
    #1
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Lubing the speedo cable might help. Lubing the tach cable will be impossible (electronic tach).

    The speedometer and tach can both be cleaned and lubricated (carefully), but you may find that the spedometer is reading low because the magnet is 30 years old. A quick fix is to make labels and stick them on the outside of the glass for the speeds that read low (place a sticker reading "60" where the speedo is labeled "50"). The tach may be slow to respond because of a break in the grey wire, or an internal fault in the tach itself. I suggest working your way backwards to the 2/3 coil to see if there is a break in the wire, or corroded connectors.
     
    Last edited: May 24, 2015
    k-moe, May 23, 2015
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  3. cutlass79500

    cutlass79500 Well-Known Member

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    The grease in the speedo head gets hard and messes everything up . I have had pretty good luck cleaning the old grease out and re lubing but that is more then likely not the problem. Usually the speedo will not work at all or bounce when the grease gets hard but you never know.
    .
     
    cutlass79500, May 23, 2015
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  4. waldreps

    waldreps Active Member

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    Mine does the exact same thing and cleaning and re-lubing didn't affect it at all. I got pulled over cause I was speeding but the state trooper let me go. He helped me figure out how far my speedo was off. It's almost 10 mph slow.
     
    waldreps, May 25, 2015
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  5. wink1018

    wink1018 Active Member

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    Did either of you install a bigger than factory sized front tire on your bikes?
     
    wink1018, May 25, 2015
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  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    It won't be the tire. You can't get a tire to fit that is big enough to make the speedometer read 10MPH slow. The magnet that drags the needle cup is no longer fully magnetized. It can be magnetized and re-calibrated by a speedometer shop. There is a DYI method, but it takes time, patience, and the willingness to risk making the speedometer read fast rather than slow.

    Being a "frugal" person, I just used a label maker to recalibrate my speedometer.
     
    k-moe, May 25, 2015
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  7. waldreps

    waldreps Active Member

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    Stock size tire on mine. k-moe, just out of curiosity, what does the DIY method entail?
     
    waldreps, May 25, 2015
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  8. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Finding the N pole of the magnetic disc in the speedometer, and rubbing a neodymium magnet on it until it is remagentized. The trick is to not magnetize it so much that the speedometer reads high. You will need a short length of speedometer cable, and an electric drill that yoo know the rotational speed of in order to check the calibration of the speedometer. If you go over you have to degauss the magnet, and that part is tricky with a homebrew degaussing system. This can be done sucessully, but it is very much a hit-and miss process. Sometimes it works perfectly, sometimes you find out that it would have been better to just send the speedometer out to a professional.
     
    k-moe, May 25, 2015
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  9. waldreps

    waldreps Active Member

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    Sounds complicated. I would have no idea how to find the N pole of the magnetic disc or how long to rub the magnet onto it. Do you have a write-up or a link to more details?
     
    waldreps, May 25, 2015
    #9

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