I have my Dad's 1974 Chevrolet C10 that he bought new. He passed in 1983. It will stay in the family at least until I pass. The gas gauge registers full until it starts to get low. Then it starts to move. The needle fluctuates until tank is empty. I know this condition does not apply to Chevys only. But. This is the only Chevy I got. And. I ain't on any Chevy forums. What can I do to determine if it is the gauge or the sender? Thanks.

 

Sounds like the sender is bad. You can pull it and try bending the float arm up, which should make it start registering fuel loss sooner. If it is fluctuating, the wire that makes up the resistor coil is probably corroded or shorted in the area it fluctuates.

If you pull it, you can put a ohm meter from the terminal to ground. They should read 0-90 ohms, and should move smoothly as you manually cycle the float from full to empty.

 

Thanks. I will try that. I hope it is the sender. I searched the net for a fuel gauge. It is the same size as the speedo. No luck. Senders? Yeah. They are available. Thanks.

 

Classic Parts has them here
Sending units for classic Chevy trucks and GMC trucks.
and the gauge here
Gas tanks and obsolete Chevy parts for old Chevy trucks.

LMC should have them also, but I can't get their website to work right now.

I bought one for my 68 Chev from Classic and it worked fine.

Generally, the gauge doesn't go bad, just the sender.