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TR2/3/3A Fuel gauge issue 60 TR3A

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BritCars54

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I had a fuel gauge that did not function. Receiving signal (ohms) from sending unit. Gauge sent off, cleaned up, repaired, and tested. Installed, wired as per diagram. Good news is that it appears to register correctly. Bad news is that it is bouncing continously. Thoughts on what be the cause welcomed.
 
Just to be clear - you mean it (the gauge needle) bounces continuously whenever the ignition is on? Or do you mean it bounces continuously when you're out driving?

Tom
 
I would suspect the sending unit if this occurs while driving. You can easily work the sending unit by using a long length of stout wire bent into an "L" and fished into the tank. With it you can push down on the sender arm or hook the arm and lift it up to see if there are some dead spots on the sender.

I suppose ideally one should use a length of copper wire for this.
 
They frequently bounce a little, as the fuel sloshes around while driving.

My first step would be to add a ground wire for the gauge. It doesn't show on the diagram, but the TR3 gauge requires a ground (unlike the later cars), and the connection through the mounting bracket just isn't very reliable. Especially if the panel has been painted. Just a ring terminal on the mounting stud, and a short length of black wire over to the ground tie point is all that's needed.

I had already disconnected the tie point, but you can see the wire and gauge in this shot:
 
Geo Hahn said:
I would suspect the sending unit if this occurs while driving. You can easily work the sending unit by using a long length of stout wire bent into an "L" and fished into the tank. With it you can push down on the sender arm or hook the arm and lift it up to see if there are some dead spots on the sender.

I suppose ideally one should use a length of copper wire for this.
Click to expand...

Or wood?
 
Ok, I missed it. Why copper or wood? A plain old coat hanger or length of "baling" wire works fine.
 
Thanks for all the thoughts. It is the needle bouncing, and much more than is typically seen. I do have the gauge grounded. Will have to check out the sending unit... I think the problem is there.
 
Wood to prevent a static discharge...in the tank. Probably won't light off anything, but there is always the one in a million spark.
 
Oh, OK. While we're checking for a bad electrical connection in a device hanging down inside the tank. Got it.
 
Not me...I was just offering a suggestion for someone who wood be so inclined
 
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I have attempted to take those Smiths BT 3331/02 fuel tank sending units apart to see "what makes them tick". I can get everything apart except the "axle" thru the case. The float & rod are one end of the axle & the arm that sweeps the coil is on the other end. That entire assembly (case, coil, axle arm & float) needs to be grounded for the sender to work. It appears as the years go by, corrosion or "crud" get between the axle & the case, causing it to lose continuity at certain spots as it swings thru its arc. That would cause the gauge needle to bounce. Since I can't remove the axle, I can't clean it up. I am able to fix it on the bench with a set of alligator clips. One successful method that I have heard of (not tried) is to solder a 24ga copper wire from the top solder joint on the arm to the case, thus providing continuity thru the arc without depending on the "axle"
That being said, New Old Stock Locators sells a correct and reliable fuel tank sender for TR3s.
Frank
 
Frank, do you have any contact info for New Old Stock Locators (NOS) in Rhode Island? Google has let me down. Thanks.
 
Arnie,
Here's contact info;
[FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif]NOS Locators' [/FONT]
[FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif]Email may take several business days to be answered -- Please be patient and plan accordingly.
For an immediate response, phone us at 1-401-725-5000 Mon-Fri. [FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif]M-F, 9:00 AM - 6:00 PM Eastern Time.[/FONT][/FONT][/FONT][/FONT][/FONT][/FONT]

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[/FONT][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif][FONT=arial, helvetica, verdana, sans-serif]
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