78 gas guage not working

[forkliftman79]

My fathers 78's gas guage is not changing from a quarter tank not dropping or raising when gas is added. Anyone have any suggestions where to start or what to do?
Thanks

 

[DeeVeeEight]

try filling the tank and bouncing the rear of the car. the sending unit may be rusted up tight, some fuel system cleaner might help too.

 

[JohnZ]

Or the bladder insert may be collapsing, jamming the sending unit float arm.

 

[TimAT]

A quick and dirty test = pull the sender wire off the tank, put a 12v testlight between that wire and a known good ground. Turn the key on and see whare the gauge goes. About 1/2 tank, the gauge is good and your problem is in the tank. With the sender wire unhooked and the key on, the gauge will go past full scale.