1956 Cadillac Fuel Gauge question

[carguyblack]

My fuel sender is no doubt trash but now I'm concerned about the gauge itself. Can anyone tell me if it is normal that the gauge pegs to completely full the instant I turn the key on, even when there is no sender unit attached? When I turn the key off, it gently floats back to empty but it lights right up and stays there with the key on.
I have a new sender unit coming but I'd like to know if I can look forward to tearing the dash apart again to replace the fuel gauge too! Thanks for your help. Chuck Dykstra, Portage, MI

[Otto Skorzeny]

Once you get it hooked up I think it will work right. The guage receives a constant electric charge when the key is on. The circuit is interrupted with the sending unit removed.

[J. Gomez]

My fuel sender is no doubt trash but now I'm concerned about the gauge itself. Can anyone tell me if it is normal that the gauge pegs to completely full the instant I turn the key on, even when there is no sender unit attached? When I turn the key off, it gently floats back to empty but it lights right up and stays there with the key on.
I have a new sender unit coming but I'd like to know if I can look forward to tearing the dash apart again to replace the fuel gauge too! Thanks for your help. Chuck Dykstra, Portage, MI

Chuck,

Ditto on Forrest comments..!

The fuel gauge is a combination of parallel and series resistance coils (in conjunction with the sender resistance) that would the gauge behave strange without the sender in line. If the needle pegs to “Full” and then returns back to normal “Empty”, it is a sign the gauge is working.

To be sure just test the gauge and sender operation before you bolt the new sender in the tank. Also, the manual shows the procedure to check the float arm under Fig 13-10.

Good luck..!

[carguyblack]

Yahoo! I sure didn't want to dig into the dash again. I'll let you guys know what the verdict is after the sender is installed. Appreciate the "second set of eyes" from you guys.
Best regards,
Chuck

[Misfit]

The correct aswer would be the ground is interrupted. With the ground disconnected the gauge will pin to full instantly.

When the new sending unit is installed, be sure you have a good clean ground between the sending unit and the tank. Often there will be a wire running from the attaching point of the sending unit to the body or frame.

Not sure how they did it on a '56.

MisFit

[Eric Falk]

The correct aswer would be the ground is interrupted. With the ground disconnected the gauge will pin to full instantly.

When the new sending unit is installed, be sure you have a good clean ground between the sending unit and the tank. Often there will be a wire running from the attaching point of the sending unit to the body or frame.

Not sure how they did it on a '56.

MisFit

The fuel line was used to ground the tank on a 56'.  The sending unit is grounded to the tank and the fuel line runs from the tank directly to the frame.  Without the fuel line attached to the frame you will need to attach a ground wire from the sending unit or fuel tanlk to the frame or the sending unit circuit will be open.

[dan reed]

Chuck - what everyone stated is correct - without that sending unit your gauge will peg to FULL. The reason I 'm writing is because I read somewhere (may have been in the shop manual or in the instructions for the sending unit I put in my '56) that you do not want to leave the gauge in that FULL Position for too long as it could do damage to the gauge. I assume your not currently driving the car, but I figured I would mention it being somewhere along the line it was an important enough issue to put in writting.

Dan

[carguyblack]

I certainly felt it was not doing the guage any good seeing it electrically charged to the max position everytime I turned the key. I have now replaced the sender as well as the guage and they both seem to be operating. I wonder if the ground fault I had in the original guage itself (that necessitated my replacing it) was caused by the weeks of intermittant starting and running, thus pegging the guage? At least this is behind me now and perhaps my experience will be helpful to someone else in the future. Many thanks for all the help! No man is an island, especially in the old car hobby! Chuck

[lowchevypickup]

what is the ohm range on a 56 gas gauge?

[J. Gomez]

what is the ohm range on a 56 gas gauge?

For early GM gauges the resistance was 0 ohms=E, 32 ohms=F. By the early 60s these were converted to 90 ohms.