The Stovebolt Site Forums The Shop Area The Electrical Bay Figuring out gauge problems?

I have recently purchased a 1955 3100 Series 1. It is pretty much all original, and almost everything works except the speedometer and gas gauge. Are there some tips on figuring out what's wrong with them? Is there an good way to tell if the problem with the speedo is in the gauge, the cable or something else? Also, is there a good way to test whether the gas tank sender, the wire or the gauge is shot? I'm pretty new at this, so even some simple tips would be appreciated.

Thanks,
Trooper Jeff

The speedometer is mechanical, driven by a cable with a squared off end that goes into the speedometer gauge and a corresponding end that goes into a gear on the side of the transmission. Frequently the cable is the problem. It hasn't been lubed in forever.

Disconnect it from both the speedometer and the transmission, then turn one end (if you can) and see if the other end turns. If it does, you should lube the cable, reconnect everything and see if it works.

If you can't turn it, try pulling it out of the cable housing. If it comes out in one piece, it's at least intact. Inspect it for kinks and frayed areas, and look at the both ends carefully. If their edges are rounded, they may be slipping inside the gears. The tranny gear may be worn out. Or the speedo gear may be worn out.

Once you've assessed the parts, you'll know what needs to be done next.

The gas gauge is driven by a very simple potentiometer (resistor). A float attaches to an arm that has a wiper that travels along the potentiometer. When the resistance is highest, the gas tank is lowest and vice versa.

You can simulate this behavior by touching the wire connecting to the fuel tank sending unit to ground and then releasing it. If the gas gauge doesn't move, there may be a problem with the wiring or the gauge. If the gauge moves, the problem is probably the sending unit or its ground connection.

The key to troubleshooting problems with systems is to learn what all the parts of the system are and figure out a way to isolate each part of the system and confirm that it's working or not working.

+1 and if I might add. Using the search function using 'gas or fuel gauge' will get you a procedure using an inexpensive variable resistor. One can use it for testing and calibrating both the fuel gauge plus oil and temperature sensors, if they are the electrical type called the 'balanced coil' vs a King-Sealy or others. A quick way to check is look at the sensors. If there is a wire attached it is electrical, a tube indicates a mechanical type.

My spedometer was not working and I found that there is a felt wick to keep the bearing oiled on the back side of the speedometer. I got that refreshed with oil and it works fine now.