The gas gauge seems accurate. However,.. the needle bounces back and forth with a bit of an erratic motion (about 2-3 needles widths) not matter how full the tank is. I'm not familiar with this problem. Seems like electrical ,. grounding ,.. or ??.? I've had one other '64. I know that this problem is not "normal".
It could be the ground or there could be a "dead" spot on your sending unit where you are not getting a reading (or a weak reading) and this could cause the needle to bounce.
is this erratic motion something that just started? In my 55 the gas gauge only stops moving when the truck is at rest. its very sensitive to motion. when it starts bouncing off the empty, i figure its time to fill up. (gauge and sender are original)
mine did that once for one entire tank of fuel .....has never done it again? I know that doesn't help much....maybe run some fuel conditioner through for a tank??
It could be the ground or there could be a "dead" spot on your sending unit where you are not getting a reading (or a weak reading) and this could cause the needle to bounce.
The car has been sitting for 15 years. So maybe the sending unit is done. ??
Gas gauges work off a graduated ground circuit The sending unit in your tank is the likely culprit. If you disconnect the wire the gauge should Go to the top and as you increase the grounding it should go down. This Checks the dash guage