C1 (60) Gas gage jumping

[Jim K.]

I have put a new grounding wire from my sending unit (which is less then three years old), but my gas gage (restored in 05 by Corvette Clocks) still jumps around. I grounded it to the metal frame structure that is under where the gas tank cover it screwed down to. There is a metal frame structure that is in the gas tank area, behind the passenger seat. The gas gage jumps from 3/4 to 1/2 indicator marks (that kind of distance), not only in that area. After filling the tank up the needle doesn't sit on the full mark. I picked up the sending unit from Corvette America.
I haven't taken the sending unit out to test the ease of movement in the sending unit arm.
This is my first old corvette, so I don't have any experience to draw on.
Any help/suggestions would be appreciated. Thank you and have a safe 4th of July.

[Jack H.]

Re: C1 (60) Gas gage jumping

Verify the gas guage itself is FIRMLY attached to the instrument cluster. Even though the circuit is from the gauge through the variable resistor in the gas tank, the gauge itself has to have a solid ground reference or the needle will 'twitch' all over the place as the gauge ground comes and goes....