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Discussion Starter #1 (Edited)
My Spider was suffering from the common wobbly fuel gauge needle problem, even after properly aligning the sending unit in the tank to face left/right rather than front back.

I've found a easy fix that greatly reduces the problem. I'm posting it here, rather than in the Spider forum, as I think it should be applicable to all 105's.

Essentially the problem comes from the sending unit float arm moving up and down too freely, and the fix is to damp that movement.

For me, at least, it's easiest to explain by showing how the sending unit works but for those familiar with that, you can skip past this part.
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Here's a picture of the Sending Unit opened up:
gas sender open.jpg

You can see that there are two copper contact arms attached to the float arm. The shorter of the two contacts acts as the switch for the red low fuel light in the gauge. When the float arm falls far enough in the tank, the arm makes contact with the housing contact and completes the circuit,lighting the bulb. The longer copper contact arm moves against the black plastic mounted wire coil which acts as a variable resistor. When the contact moves up and down the coil, the variance in resistance causes the gauge needle to move in reaction. The wobbling action in the needle is caused when the fuel in the gas tank sloshes and the float arm moves too freely with the sloshing.
The possible answers to this are either to stop the sloshing or damp the movement of the float arm.
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Stopping the sloshing in the tank is possible, but not cheap or easy. Damping the motion of the arm is easily accomplished by increasing the friction of the longer copper contact arm against the variable resistor in the sending unit. Whether designed with adjustment in mind, or by happy coincidence, the position of the variable resistor can be changed to increase the friction between it and the the arm. Look at the picture below and you can see that the black plastic resistor unit is held in the white housing by two tabs:
gas sender 2 back.jpg

By pushing those tabs inwards from the back of the sending unit with a small screwdriver, you can reduce the distance between the resistor and the swing arm, increasing the friction,and damping the motion of the float arm.

gas sender back.jpg

With the increased friction, the pressure of the liquid against the float will still move it upwards, and gravity will move it downwards, but less easily. You'll still get some movement in the gauge from curves or from sudden acceleration / braking but the gauge will move from its proper position once and then return, rather than waving back and forth like a drunk with a five-dollar-bill trying to get the attention of a stripper.

In my case, I'd already decided to increase the friction against the arm by using a stronger spring inside the sending unit before I realized that the black tabs allowed for friction-level adjustment without disassembling the unit. I'd save this for a level-II fix, if you don't get enough damping from adjusting the position of the resistor using the tabs.
gas sender springs.jpg
You can see the small original copper spring and the stronger one I used to replace it. The function of this spring is to push the float arm against the resistor. I found the original spring a little weak and allowing a tiny bit of slop.

Before reinstalling the sending unit, make sure to test the float arm motion by lifting it and letting it drop, Note that it shouldn't move too freely. That was the problem to begin with. Remember however that the pressure from the gas will lift the float, and that gravity and small bumps in the road will make the float arm fall and those forces are pretty strong. Still, not too tight or you're going to run out of gas some time because the arm didn't fall all the way to the bottom. The perfectionist answer would be to have the resistor slightly ****ed towards tighter at the top and looser at the bottom.

Hope this is of use in at least starting a discussion. Anyone have any alternatives or improvements? This has worked pretty well for me in reducing what was a real annoyance. I no longer have to park the car to get a reasonable idea of how much gas I have left.
 

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This is a great item. More damping like this probably just the thing. Thanks, will try it on my next problem car.
Andrew
 

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hi there

I realise this is an old thread.but I have just dissassembled my floating devise and ai left with the spring. I am not quite sure where it should go??
 

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Clever

Pete
 

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Do you think that the additional contact pressure will increase the wear rate of the resistance wire?

Tom Gubi has some big capacitors wired to his sender which dampen the electrical signal to achieve the same effect.
 
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