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Thread: 280z Voltmeter show positive volts even when disconnected!

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    Default 280z Voltmeter show positive volts even when disconnected!

    Hey there-

    Just inherited a '76 280z from my elderly (83) father. Of course the clock isn't working and hasn't for 15 years or so. But I also noticed the voltage gauge was almost pinned at the right of the gauge. I read the forums about bad voltage regulators, etc., so I went out and tested at the battery with a multimeter. The battery was reading 12+ with the car off. And a little more when running, and topped out at 13.7 or so when the car was held at a steady 2500 rpm. Okay, so relief there.

    Then I found a post about adjusting the gauge with a screwdriver from the back. This allowed me to move the needle from dead right, but the range of the adjustment wasn't near enough to get the needle where it should be. So thinking there was a short I disconnected the gauge and used the multimeter to probe the leads running into the gauge. Same reading as battery. And that's when I noticed something strange. The voltage gauge was reading a positive 6-7 volts or so while disconnected. And not coincidentally, that is almost exactly how far off it is at the other end when connected.

    So the gauge won't "zero". I took it out of the bezel and it looks like a very simple analog gauge. I can understand why when power is applied it is deflected to the right. But I don't understand what would cause it to float above it's little bump stop when there is no power running to it at all. And it's not frozen there. While handling the gauge it freely bounces around, and when I had it out of the bezel, I could easily push it over to the left with my finger.

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    Any help would be appreciated.

    Tai

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    No more body roll! SteveJ's Avatar
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    IIRC, the needle of the voltmeter, if it works like the other gauges, is on a spring to pull it back to 0. When voltage is applied, the needle is pulled to the right as you face the front of the gauge. It wouldn't surprise me if the spring has lost tension over the years. Remember, that the voltmeter reads voltage even when the car is off, so the spring would constantly be under tension.

    Remedies:
    1. Try to find a good used voltmeter. (Just make sure the fuel gauge works on it, too.)
    2. Change to VDO meters.
    3. Get the old meter repaired. I know I posted a link for Bob's gauges or Bob's Speedometers somewhere. You can Google it, too.
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    This is a WAG (wild ass guess) but I wonder if the spring might have hopped out of its retainer at one end?

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    I recommend calibrating it at 12V with a depleted battery or power supply which reads 12.0V on a DVM.

    Then check it with a 9V battery or variable DC supply for correct functioning.
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    The needle can get twisted on the little "motor" that rotates it. If you're patient and good with tiny things you may be able to reset it on the shaft. Or send it to a speedo shop. Or find a used one on Ebay (fastest & cheapest of all).

    Either that or you've discovered an UNLIMITED source of FREE electricity, and you're GONNA BE RICH!!!

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    Okay, so here's an update. I got a magnifying glass and took a very close look at the thing. There is a very small wound copper spring that returns the needle to zero, or in this case, 4. Through age and constant voltage holding it in the middle its travel it seems it has sprung a bit and needs to be tightened a little. One end of the spring is attached to the needle (in the middle), and the other end (outside) is attached to a little gray arm that comes down from the central shaft. The spring end appears to be soldered to it. There is a very small screw at the top of the central shaft. It has something like beeswax or a very light glue over the top of it. It looked for all the world like I could loosen the screw a little and rotate the little arm to tighten the spring.

    Wrong! I loosened the screw just a couple of turns and the needle, spring and everything except the arm came loose. And it now appears the arm is in a fixed position and to tighten the spring you would have to unsolder it and resolder it in a new position.

    So I think I will take it and the non-working clock to a watchmaker to see if they can reattach it and tighten the spring up for me. I can't even get the needle rethreaded at this point with the tools I have, and I don't want to buy a bunch of stuff just for this. Will let everyone know once I get it looked at.

  7. #7
    No more body roll! SteveJ's Avatar
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    You may want to consider specialists for repairs. Zclocks has an excellent reputation for repairing Z car clocks. A friend of mine on this site has used Bob's Speedometers for his tach and had rave reviews on the quality of workmanship.
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