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1993 940 Fuel Gauge ruminations 900

posted by  yenna on  Tue Oct 13 03:55 CST 2009
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last visit: Tue Dec 7 09:42 CST 2010
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I have an intermittent fuel gauge (sender ohms reading always appropriate). Recently, it works much more reliably when ambient temp is lower. I've read here that one fix to troublesome mounting/electrical contact screws is to solder the connections. The reasoning was that Volvo used some weird metal for these screws and that it would corrode or something. My question: has anyone tried substitute screws? For example, would stainless steel be a logical next step?
(I am hesitant to solder to the flexible circuit board on the back of the cluster.)

Thanks.








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    1993 940 Fuel Gauge ruminations 900

    posted by  Arthur on  Fri Nov 13 08:44 CST 2009
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    last visit: Sat Aug 2 07:35 CST 2014
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    I too spent about a month chasing this problem, the gauge worked when cold, and quit after about 15 mins. Cleaned the screws, sandpapered the connections, also the connectors to the back of the cluster. No joy. Then I examined all the printed circuit solder joints with a high power magnifier, and found a couple of bad ones, not near the gauge. Soldered them up (it is easy), and the gauge has worked well ever since (9 months now). Personally, I don't think the screws are much of a problem. Clean them up and if the gauge still doesn't work, then look elsewhere.

    Good luck.

    '94 940T 251,000 km







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    1993 940 Fuel Gauge ruminations 900

    posted by  rstarkie on  Tue Oct 13 04:19 CST 2009
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    last visit: Fri Oct 24 10:14 CST 2014
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    I purchased a 1994 940t in June whose fuel gauge was intermittent (more often than not it did not work). I, too, was uncomforable with soldering the screws.

    I used a scuff pad (auto body supply) to clean up the contacts on the circuit board. I also used the scuff pad on the screws and the contact surface of the washers.

    It worked!.... for a while. Now the gauge is intermittent again (but more often than not it works).

    I am with you on the replacement of the screws, but I was thinking more along the idea of ones made from copper. Surely someone in the metric world has produced screws of that size and pitch for electrical contact applications, the task is to locate them.

    Good luck and let us know if you find a substitute.

    Randy








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      1993 940 Fuel Gauge ruminations 900

      posted by  spook on  Tue Oct 13 13:16 CST 2009
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      last visit: Fri Oct 24 08:06 CST 2014
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      Dear Randy,

      May this find you well. The problem may be that the undersides of the screw heads are not smooth, so do not make complete contact with the circuit card. Brass oxidizes. An invisibly thin layer of oxide will break the circuit.

      Solution: check the undersides of the screw heads. If there are small burrs, remove them with fine sandpaper. Remove any dust, by washing with solvent (e.g. methyl ethyl ketone [very flammable]). Apply a thin film of di-eletric grease to the underside of the screw heads. This will inhibit corrosion.

      Hope this helps.

      Yours faithfully,

      Spook








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        1993 940 Fuel Gauge ruminations 900

        posted by  rstarkie on  Tue Oct 13 14:09 CST 2009
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        last visit: Fri Oct 24 10:14 CST 2014
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        Spook,

        The image shows the configuration of the screws with flat and lock washers. I do not know what the material is but it is not brass. The next time I have the opportunity to remove the cluster I will buff them up again and try a little dielectric grease.

        Randy

        Photobucket








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          1993 940 Fuel Gauge ruminations 900

          posted by  GAcyclops on  Tue Oct 13 16:35 CST 2009
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          last visit: Sun Jun 29 13:55 CST 2014
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          Dielectric grease is an insulator, designed to inhibit electrical conductivity - that is why it is used on spark plug boots (but NOT the clip inside the boot), to prevent arcing from spark plugs to other metal parts.

          If you want good electrical contact, do NOT put dielectric grease on contact surfaces. You can, however, use it as a protective coating OVER the completed connection ... just NOT between contact surfaces.

          I removed the screws from my instrument cluster, used very fine steel wool to polish the copper contact surfaces and a Dremel wire brush on the screws, then put small amounts of WD40 on both.
          I believe the original design for the screws was cadmium, but was changed.








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            1993 940 Fuel Gauge ruminations 900

            posted by  rstarkie on  Wed Oct 14 00:19 CST 2009
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            last visit: Fri Oct 24 10:14 CST 2014
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            It is my understanding that dielectric grease was not designed to promote conductivity but rather maintain it by preventing exposure to moisture and air that might degrade it.

            I have never had a connection fail to make contact because it was coated with dielectric grease. I would suggest that in the case of spark plug boots the purpose of the grease is to prevent the intrusion of moisture rather than prevent arcing (it also does a great job of not allowing the boot to become "stuck" to the porcelain).

            I think that by cleaning up contact points (in this case the circuit board and screws)and then tightening the screws any grease that would be preventing contact would be squeezed out of the way. At that point the grease would be protecting the connection.

            I am not a fan of WD-40 for purposes other than displacing moisture. I was unaware of its use on electrical contacts.

            I do like the idea of using a dremel/brush to clean up the screws. Seems like holding the screwhead in a vice and using the wire brush to clean them would be better than simply scuffing them up with the abrasive pad I use.

            Randy








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              1993 940 Fuel Gauge ruminations 900

              posted by  BobfromPA on  Fri Nov 13 07:32 CST 2009
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              last visit: Mon Dec 28 07:41 CST 2009
              [RELATED]

              The fuel gauge in my 940 is flaky, too. How do I remove the cluster to get to the screws?








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                1993 940 Fuel Gauge ruminations 900

                posted by  rstarkie on  Fri Nov 13 08:00 CST 2009
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                last visit: Fri Oct 24 10:14 CST 2014
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                http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#940InstrumentClusterRemoval

                That link will take you to where the cluster removal is discussed in the FAQ's. The photo shows the angle of attack to push the spring clip back to release the bezel on that side. It is the same attachment on the other side but only one needs to be released.

                There is a small slot on each side of the bezel that you can insert your long thin screwdriver into to press on the spring. It takes more pressure than you might think and then the screwdriver seems to be in the way and holding it in- a little determination on your part will cause the bezel to be released.

                Randy








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                  1993 940 Fuel Gauge ruminations 900

                  posted by  BobfromPA on  Tue Dec 1 09:07 CST 2009
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                  last visit: Mon Dec 28 07:41 CST 2009
                  [RELATED]

                  With the help up the link you provided to the FAQ, I was able to remove my cluster. Everything seemed tight, though, so I just put it back together. I guess it will take some serious short checking.

                  Thanks.






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