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Gas gauge sender for triumph

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  • Gas gauge sender for triumph

    My musical friend has a Triumph TR-3 with a bad sender for the gas gauge. It is wirewound on a form about 1/2" diameter and about 2" long and enclosed in a brass can. A cork float is attached to the arm which moves the wiper up and down the wirewound coil. Does anyone have any idea what type of wire is used? What resistance would that coil have? Maybe we could use a wirewound potentiometer with about four times the resistance and use about 1/4 of a turn from the arm and float. They still make these and I would just go buy one if it were mine but my friend is a musician(translation=has more time than money) and I don't mind the challenge. Thanks--Mike.


  • #2
    I've seen those senders being used as a variable resistor in series with the gauge, in other words, a two wire device. If that's the case with yours, you'll need to closely match the resistance so the indication is nearly correct. If it's used as a potentiometer, which will need three wires, it's less critical, but still should be close. If you can post a bit of a schematic of the fuel sensor wiring, that should help to clarify what you might be able to replace it with.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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    • #3
      What ever happen to carrying a stick that has graduations on it, indicating the level of the tank? May be crude but some people still do these things. I think the gas delivery folk still have to measure the tanker level with a stick.


      Jerry

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      • #4
        Jerry, you're showing your age. My Model T has a "stick" as you describe.

        Mike - Nickel Chrome (Nichrome) wire is usually used in those senders. I don't have the specs on the sender resistance but it could range from 30-90+ ohms. If you could find that out, all you do is buy the wire (Probably 30ga.) and use a length that matches the resistance. By the way, that stuf is NOT cheap in small quantities.

        You could get a 100 ohm wire wound pot* and use that to determine the E/F sweep. Then just measure the ohms of the pot.

        * www.allelectronics.com has these for $1.00.

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        • #5
          Perhaps the fuel tank (sending) unit is similiar to the one in my 1961 MKII Jaguar sedan. I had need of improving its result some years ago and disassembled, cleaned and reassembled it. Since then, it has worked perfectly. I did take some measurements actoss the slide wire at that time and found that it tested at 200 ohms with the tank empty and 14 ohms with the tank full. This is to say the float is down or up respectively.
          So, what is really the issue with the Triumph gage? Just repair it and it should work well.
          ralphe

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          • #6
            If you have the old one,then why not clean it and make sure the contacts are making and see if it works?
            I just need one more tool,just one!

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            • #7
              The old sender is beyond help. The windings are broken and sagging away from the form. The wire is very thin and would be hard to work with. The arm has a lot of slop in it so the wiper doesn't stay on the coil as it arcs up and down. I may be able to bush the arm pivot to take up the wear but I need to figure out what the wire is to rewind the form. The wire looks copper-colored but someone suggested nichrome wire which is silver. More experiments are in order.

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              • #8
                Dear Sir:
                Take an ohmmeter and measure the resistance of the remaining portion of the resistor. Then estimate what the total resistance of the unit should be based on the percentage you have measured. Use a mike to get the wire diameter. You should be able to reproduce the original unit with a bit of effort!
                Regards,
                Jack C.

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                • #9
                  Why not just modify the sender so that it gives an empty indication when the tank is down to about 1/3 full. Much easier to do than trying to rewind the sensor. Just experiment with a couple of resistors to make a divider that make the guage read full until it reaches the 1/3 level at which time it drops to empty. That is all I had on my Morris Minor, no gas guage, just a light, and it was good enough.
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                  • #10
                    Had to do some research awhile back on fuel gauge senders for an additive dispenser project and found that most senders and almost all old ones are 250 ohms full scale. However full scale can either be empty or full. There are not that many variations out there and if you do a web search, you can easily find a few companys that have replacements.

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                    • #11
                      On some cars the gauge itself can have an adjustment to calibrate it to a sending unit.

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                      • #12
                        Good point,he may just be able to do that,or for that matter get a sender and guage out of another vehicle and modify to fit.
                        I just need one more tool,just one!

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                        • #13
                          Once needed some small diameter nichrome wire. Bought a cheap 110V 15 watt soldering iron from radio shack or walmart. Seems (IIRC) resistance was 11 ohms/foot and there were several feet of wire.

                          Once you get your grubby hooks on the wire, connect it to your existing wire and slide the wires on the resistance wire till gauge reads what you are looking for. THen wind and epoxy the winding. I HAVE found the resistance as described. Never wound a sending unit.

                          Last gas gauge I worked on was a newer van, (35 gallon tank). Man had pump problems. New pumps did not last. His mechanic had replaced pump, but not the filter sock and the sock jammed the gears in the pump. ANyway, his gauge read way off- at 1/4 tank he was either empty and wife always kept driving cause she "knew she had gas by the gauge or it still had 1/4 tank gas at empty and wife kept driving cause she knew the gauge was lying. Any way, since the tank was on the ground, we calibrated the float as below:

                          Extend the wires so you can hook the sender up as it will be used. Measure to bottom of tank. clamp the sender to a support and put another support where the tank bottom would be. Just bend the float until it reads empty when full down (actually we left it reading empty when he had two (plus minus) gallons reserve when the "reserve" light came on.

                          Were I working on an old unit, I would get a unit from "pull-a-part" or even buy one new, use the old mounting plate and silver solder the original plate to the replacement unit.

                          Most units (andI have worked on several through the years have 90 ohm or 70 ohm sending elements ((Again from memory) some have provisions to adjust the float arm length, some do not. Bending or cutting/ silver solder will adjust arm length and rise so most any gauge will work fine (correcting for half full and the quarter tank marks may be impossible due to tank shapes.

                          Electrically you should check to see what voltage is used- some use 12 volts (or battery voltage) some reduce the voltage (usually to five volts). Get the gauge and voltage controllers operating before working on the sender.

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                          • #14
                            Have you checked Hemmings Motor News? I'd be surprized if someone wasn't making a replacement unit. Being able to afford it, is another matter, of course....

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                            • #15
                              Try here:

                              http://www.uneedapart.com/used-triumph-parts.php
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