My gas gauge continues to be a problem

Question:

I have a 1969 Chevelle with a Super Sport dash. The gas gauge did not work, but after reading the Auto Restorer article regarding the problem in the 1955 Chevy I crawled under my dash and found the ground wire to be broken. I replaced the wire thanks to your article and the gauge now works but there is still one problem. When the wire was broken, the needle went up past full. After I fixed the wire the needle will go down as fuel is used, however when the tank is full the needle goes way past full. I tried disconnecting the ground wire when the needle indicated full, filling the tank and reconnecting the ground before starting the car. It did not help. Any suggestions to get the needle back to the correct position will be appreciated.

Answer:

The problem you’re experiencing with your fuel gauge reading way past the full mark when the tank is full is most likely due to a faulty sending unit. Connect a sending unit that you know is working correctly to the wiring at your gas tank and move the good sending unit from one extreme to the other while watching the gauge behavior to determine if the gauge reads correctly. If it does not read correctly with a sending unit that’s definitely working properly then the problem is the gauge’s calibration.

Though I don’t think it’s the source of your problem, a common fuel gauge system malady worth mentioning here is a break in the wire to the sending unit.