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How to smooth out a jumping fuel gauge?

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L

Legal Bill

Jedi Knight
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The Smiths fuel gauges always jump around, especially once you get under a quarter of a tank. Doe anyone make a condensor kit of some kind that would smooth out the electrical signal to the gauge?
 
Bill,

I had the same problem a while back and found the problem was slight fluctuations in power from the sending unit. I cleaned all wiring connections and added a ground from chassis to the tank sending unit. You may also need to clean the coil slide in the sending unit.

I still need to tap the gauge when first turning the key to get the needle to register, however, everything is stable from there….oh, except when taking a sharp turn or make a sudden stop.

Ray (64BJ8P1)
 
This might be helpful !
While helping a Healey 100 owner, there was a problem reading the fuel gauge because the needle would jiggle and be erratic. Checked the gauge itself - OK. Pulled the sender from the tank. Moved the float arm manually , gauge read properly ! By chance I wiggled the float arm and experienced the same erratic behavior, similar to the behavior when in the tank. Apparently the pivoting float shaft must be in complete contact with the sender body for continuity. This shaft is part of the "fingers" that contact the windings of the rheostat and must have continuous ground.
Made up a ground strap that is soldered to the float arm and connected to the sender body. The ground strap is a "desoldering braid" from Radio Shack and does not interfere with the float operation.
This may not be the solution for everyone, but it completely solved our problem.
Charlie Hart

100-0344_IMG.JPG
 
In an attempt to find out why my gauge needle fluctuates, I found an article about this very same topic on the web last year. Charlie, did you write that article?

So I gave it a try.

It did not make a difference for me, but it seems it did with the 100 owner, good for him!

Here's a couple photos of what I did.
 

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I should have been more clear. I am quite certain my gas gauge "jumping" is due entirely to gas sloshing around in the tank. There is nothing between the sender and the gauge to moderate the "signal" so the needle reacts accordingly. I think most modern cars have addressed this with some type of damping of either the signal or the gauge movement. That is what I'm looking for. I had my gas tank rebuilt to make sure it was gas tight. They open the tank right up, repair any corrosion and then reassemble it. But they remove the small baffle that reduces the sloshing in the tank. I think that has increased the irregularity of my gauge.
 
Hey Guys what this gadget is -is called a Voltage stabilizer just about every JAG will use one they have to be matched to your guage and they smooth the voltage input to the guage out. The swing we see is due soly to the fuel sloshing around in the tsnk.---Fwiw--Keoke
 
I purchased the gauge damper suggested by Steve Gerow and it worked as advertised. Easy install.

Lin
 
I read that if you install a 400 microfarad capacitor in parallel with the guage, it will act as an averager and slow down the jumping. I don't know if this works or not. They are cheap, might be worth a try. I might do this myself. I have a jumping fuel and speedo!
 
Our gauge didn't jump at all over the summer: got it back from rebuilding just before pulling it out of storage, and got one very big spark installing it (ignition off; battery not switched off, drat!)and it didn't jump or move for the rest of the summer. Pulled it out last week and tested the gauge (per some notes on the Forum) and it tested okay; tried getting some readings on the wires from the sender but nothing that made sense to me, so reinstalled to see if any magic had occurred, and still read nothing. Fired the car up today to move it - and I've got half a tank of fuel! And nothing with the key off! Dumb owner + the Prince of Darkness + dumb luck?
I'm looking forward to filling it up, and seeing (if) it reads full!
Doug
 
A jumping gas gauge seems to be an issue that quite a number of classic car (from Mustangs and Corvettes to Porches) owners are experiencing. Like me, most are living with it. However, as has been indicated, it is not a gauge problem but the lack of proper gas tank baffling around the sending unit float.

To eliminate this problem, some cars manufacturers have installed their sending unit float in a tube where others have addressed the action at the gauge. When the VW Beetle first provided a gas gauge, they baffled the gauge by used a bimetallic heated element in the gauge. Other manufacturers have created circuitry that would reduce responsiveness by averaging out the sending unit signal over a period of a number of seconds. And still others (United Instruments aftermarket gauges) simply install a thick silicon lubricant to dampen the needle. I believe what Bill is looking forwhat Lin seems to have found, a baffling circuit matched to the Healey's gauge and sender.

Bill, although this seems redundant base upon Lin’s success, I would suggest when you make sure the manufacture specifically states it will handle the Healey’s gauge and sending unit and will provide, or adjust, to giving correct readings throughout the full range. Additionally, check to see that it will handle the initial surge when the care is first turned on with a full tank. I was told condition could cause circuit and gauge burn out.

Hope this helps,
Ray (64BJ8P1)
 
My car is negative and I frankly don't remember if there was a polarity issue or not. This is the URL for the item and the company that sells it. It was intended for a mid-fifties porsche through early sixties. I don't disagree about the sloshing at all but this little device did eliminate erratic swings. Not perfect, but much better than without. I would give Zims a call and ask them about polarity if you are interested. It is a $20 item.

Lin
https://www.allzim.com/acatalog/copy_of_Fuel_Gauge_Stabilizer.html
 
RAC68 said:
A jumping gas gauge seems to be an issue that quite a number of classic car (from Mustangs and Corvettes to Porches) owners are experiencing. Like me, most are living with it. However, as has been indicated, it is not a gauge problem but the lack of proper gas tank baffling around the sending unit float.

To eliminate this problem, some cars manufacturers have installed their sending unit float in a tube where others have addressed the action at the gauge. When the VW Beetle first provided a gas gauge, they baffled the gauge by used <span style="font-weight: bold">a bimetallic heated element </span>in the gauge. Other manufacturers have created circuitry that would reduce responsiveness by averaging out the sending unit signal over a period of a number of seconds. And still others (United Instruments aftermarket gauges) simply install a thick silicon lubricant to dampen the needle. I believe what Bill is looking forwhat Lin seems to have found, a baffling circuit matched to the Healey's gauge and sender.

Bill, although this seems redundant base upon Lin’s success, I would suggest when you make sure the manufacture specifically states it will handle the Healey’s gauge and sending unit and will provide, or adjust, to giving correct readings throughout the full range. Additionally, check to see that it will handle the initial surge when the care is first turned on with a full tank. I was told condition could cause circuit and gauge burn out.

Hope this helps,
Ray (64BJ8P1)
Click to expand...
Pretty sure that's what was fitted to all==ALL MGBs. The wiring connection being virtually identical in both cars. With all the MGBs I've had (close to twenty...) you'd think I'd have an <span style="font-style: italic">Instrument Voltage Stabilizer</span> laying around, except they never went bad...
 
Thanks for all the help here, guys. I know very little about electricity and electronics. I assume someone who does could tell me if the capacitor concept would work with a positive ground system. I'll call the supplier and see if they know anything.
 
Legal Bill said:
Thanks for all the help here, guys. I know very little about electricity and electronics. I assume someone who does could tell me if the capacitor concept would work with a positive ground system. I'll call the supplier and see if they know anything.
Click to expand...

Depends on the capacitor type. Some capacitors, like tantalum, don't care about polarity. Electrolytic capacitors, OTOH, are destroyed immediately--usually resulting in a dead short--if the wrong polarity is applied. Electrolytic capacitors are cheap but usually larger than comparable tantalums, etc. Based on the size and shape of this unit I doubt they use an electrolytic, but you should find out before purchase if polarity is an issue (it may just be a matter of connecting differently). This unit probably has a resistor as well, to slow the charging of the capacitor. Resistors care naught about polarity.

Please let us know what you find out. Others (me) might be interested in getting one of these.
 
This unit probably has a resistor as well, to slow the charging of the capacitor. Resistors care naught about polarity.


This is true and a passive device such as this could be designed to supress the voltage swings that the meter would normally see.

However, the Voltage stabiliser is simply a small vibrator that is not voltage sensitive and will change a pulsating dc voltage into a non-pulsating one, The coversion will be compatible with the polarity set up of your guage.--Fwiw--Keoke
 
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