57 Belvedere fuel gauge and sender accuracy

Rusty Muffler

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Petaluma, Ca.
Before I put the new gas tank in I temporarily hooked up what looks to be original sender from where the wire plugs to it under the car and of course grounded it and turned on the key and watched the gauge work from empty to full and around halfway while moving the float arm. I also checked the cork float in a bucket of water and it stood right on top of the water. I figured that's close enough to tell me it has "some" buoyancy. (I know gas is different but by how much?)
Well I installed the tank and put 5 gallons in. Gauge moves up to just the right edge of the empty circle on gauge. I put another 5 gallons which should read half a tank but it only reads an eighth of a tank or about an eighth of an inch to the right of said circle.
I figure either the cork float has very little buoyancy or the little wiper contact inside the sender isn't make contact while in the gas? BTW, I have 2 senders that have slightly different design. The one I installed and worked has a barrel shaped winding and the extra one that reads dead has a flat board with a winding wound around it. Don't know if one is better than the other or if it even matters? Thanks for listening and yes there's a separate ground wire clamped right to the sender. At 65 and had a lot of cars, I'm beginning to think old cars suck. :)
 
Everything works on voltage and resistance. Are the rheostat coils clean and such? Is the "wiper" clean and in good shape? Other wiring connections in good condition? Can a metal float be installed in place of the cork?

CBODY67
 
Everything looked good, but the test is what counts in my mind. My next test is to fill the tank and see what the gauge reads.
 
Ok, I filled the tank and the gauge went up to about 3/4+. Funny, the gauge acts a little haunted by wavering around a little like it's possessed. I'm going to live with it like that.
 
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