1965 dart fuel gauge doesn't read correctly

[easyrider]

My fuel gauge doesn't read correctly. I had the fuel tank out today and I pulled the sending unit. I plugged it up and the gauge only reads half full with the float all the way up to the stop. At mid point, it reads empty. Is there any way to calibrate the gauge?
easyrider

 

[MoparMike1974]

Start by running a good ground wire from the tank to the frame. It can be temporary for testing purposes or permanent. Use a jumper cable....whatever works.

 

[easyrider]

Start by running a good ground wire from the tank to the frame. It can be temporary for testing purposes or permanent. Use a jumper cable....whatever works.

I have a jumper wire from the sending unit to the body.

 

[MoparMike1974]

I have a jumper wire from the sending unit to the body.

Are you sure its a good connection? Not just the factory strap, they tend to loose connection. Once your sure of the ground, check the sending unit wire for good connection. Pull it off and make sure its snug on the post. Slide it on and off a few times to clean the connection.
Is this an original sending unit? Sometimes you have to pull them and clean off the winding. Also inspect the wiper, sometimes they can wear a hole right in them. If the wiper is ok check the tension. You can carefully bend the tab to get some more tension of the wiper to winding.

 

[67Dart273]

Use you ohmeter and disconnect the gauge wire. Measure the resistance of the sender. There are bullions and bullions, boolians and boolians, ballions and ballions.......of threads on this issue

This is a shopped photo of the destructions on a gauge tester, with the resistance values added in.

 

[Rustyfish]

67dart273 are you blue in the face yet? hahaha

 

[RedFish]

First point... The duty cycle of a fuel gauge is a lot different from the others. Inside any thermal gauge is a bi-metal beam that bows with heat to move the needle. The heat comes from a resistor wire wound around the beam. That wire had a spiral wound goldish color insulation that is barely visible. In a lot of cases that insulation becomes caked with crud. It limits beam movement much like a cast on a arm. It accumulates heat and overheats the beam too. You can't know if this is your condition without pulling the inst' panel. if you find what looks like black pepper laying in the bottom of that gauge... there's your 1st sign.
Opening the gauge you might reveal a beam bowed at room temperature. The sad part... it can't be cleaned and/or corrected. You would likely break the insulation and short some portion of the wire to the beam. If you find a good bit of black pepper debris in the bottom of the gauge, that short could have happened already.