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The cluster on my 63 was recently restored so I'm sure it's in the sender. When I fill up the tank and am sitting still the gauge works fine and indicates full. However, the minute I move the needle starts bouncing all over the place.
Anyone experience this and other than replacing the sender have a suggestion for a fix.
There should be some movement in the gage due to sloshing in the tank but not all over the place. Does it read half full when when the tank is half full?
You might try cleaning and tightening the brass terminals at the sender and making sure you have a good ground contact at the sender (black wire connector).
A test of the sender on the car is to put an ohmmeter between the two brass terminals. With the float up or full tank, the meter should read about 90 ohms. With the float down or empty the meter should read 0 ohms or full contact.
If the ohms test works and the gage still jumps around, it could be a grounding problem at the sender terminal, or in the wiring to the gage.
Hopefully, it's not one of those overseas made senders. If so, don't use too much force in removing the terminals, they are just press fitted in. The original senders have a threaded shaft on the terminals and a nut to hold the terminals in place.
Good Luck
Jerry Fuccillo
#42179
Jerry Fuccillo
1967 327/300 Convertible since 1968
I'm experiencing a similar problem with irratic readouts in my '65, and am about to replace the sender with an AC Delco replacement. The problem started out like yours, then deteriorated to the point that the gauge almost never reads accurately.
I diagnosed the problem as being the sender by inserting a stiff piece of wire into the tank when it was half full (so the float is level with the rheostat) and moving the float (I bent the end of the wire into a circle whose diameter was a bit larger than that of the cylindrical float). I noticed that when moving the float through its range of motion while applying a little pressure - pulling it towards the rheostat - it read correctly. Doing the same while pushing it in the opposite direction - away from the rheostat - it read incorrectly - an obvious sign of excessive wear at the float arm's pivot point in the rheostat.
By the way, the rheostats are rated at 90 ohms. I bench tested the new one between 0-110 ohms through its range of movement, which I assume is within tolerances.
I bench tested the sender before installing (it's the original) and was getting between 0-90ohms. HOwever, this was moving it slowly. Seems when It sloshes is when it goes kabut. HAte to replace it but looks like it will have to go. Will double check the ground before doing so though. I checked the other connections and they are fine.
Before you trash your original, check inside the varible resistor housing for dirt or contact problems of the contactor against the resistor windings. There is an article in the summer 2004 Restorer for a C3 sender, but the same principles apply.
Jerry Fuccillo
Jerry Fuccillo
1967 327/300 Convertible since 1968
My 67 gage fluctuates more then normal & when I turn key off the needle does a 180degree flip! BUT it give a accurate reading. Been doing this for a year or so. I cleaned all contacts. No help.
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