The Ford Barn

WQ59B · 06-06-2017, 09:56 PM

Have an all stock '40 COE 239. Still 6V, all original gauges. This truck has been an amazingly willing resurrection candidate- most components when opened/disassembled have been extremely clean & operable.

Changed out the original gauge cluster with a much nicer one bought at Hershey, but apparently burned the delicate wire inside the gauge when had problems last year blowing fuses. Today I put the original gauge back in after verifying the internals were electrically OK. Also taped the edges of the rear gauge cover to insure no grounding out or other electrical issues.

Original sender is clean & working, brass float is air-tight.

However, when running today the fuel gauge wavered quite a bit between the bottom mark on it's scale (empty) and a quarter tank... tho looking into the top of the tank I had 33-40% of a tankful (via the drilled internal center baffle). Ran truck for about 4 minutes and gauge didn't settle down, kept wavering inconsistently. Tank sender is grounded to cab.

I know about the adjustment 'gears' inside the gauge but MAN is it a PITA to get to the gauge back in a COE! Is there any other suggestions or causes of an unsteady reading??

Oh, and I could live with a 'gauge stick' if the COE didn't have a 45-deg bend in it's filler neck. :/

Drbrown · 06-07-2017, 12:32 AM

After fiddling with the gauge, you've gone after the obvious, the send unit. OE senders are getting hard to find. Have you removed the sender unit and held it horizontal while slowly raising and lowering the sender arm while watching gauge ? You can do that sitting in the cab by using some jumper wires. Try lightly spraying the interior parts of the sensor with electronic cleaner. If you get any kind of a reading on the gauge I suspect that at least there's no "break" in the interior sensor.

Otherwise, sitting in the cab with the sender using a pair of jumper wires (ground and sender connection) connected direct to gauge terminals would indicate if you you had loose or faulty wiring between the gauge and tank.

Try substituting the gauge with one known to work. I have a spare stock mid-1940's you could borrow (mail back and forth ?). The gauge internal part may even be interchangeable with yours.

Note: After the "fix" is found/complete, use a gas-compatible sealant on your sender unit gasket (not all are) when installing it.

WQ59B · 06-07-2017, 05:21 PM

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I don't have a known good one, only have 2 & 1 is 'known bad'.
All wiring is brand new. Will look at testing it as you stated... I did try the sender on a known good oil pressure gauge, to see if the float arm moved that needle, and it did. Don't know why this assembly is causing the needle wavering.

I read a bunch of threads where folk here recommended cork for the tank gasket. I have rubber there but when I took the sender out last week, it did look whitened with some cracking. Going to replace that with cork... or can I use gasket paper?

06-06-2017, 09:56 PM	#1
WQ59B Member Join Date: May 2014 Location: NJ Posts: 69	'40 Fuel gauge Have an all stock '40 COE 239. Still 6V, all original gauges. This truck has been an amazingly willing resurrection candidate- most components when opened/disassembled have been extremely clean & operable. Changed out the original gauge cluster with a much nicer one bought at Hershey, but apparently burned the delicate wire inside the gauge when had problems last year blowing fuses. Today I put the original gauge back in after verifying the internals were electrically OK. Also taped the edges of the rear gauge cover to insure no grounding out or other electrical issues. Original sender is clean & working, brass float is air-tight. However, when running today the fuel gauge wavered quite a bit between the bottom mark on it's scale (empty) and a quarter tank... tho looking into the top of the tank I had 33-40% of a tankful (via the drilled internal center baffle). Ran truck for about 4 minutes and gauge didn't settle down, kept wavering inconsistently. Tank sender is grounded to cab. I know about the adjustment 'gears' inside the gauge but MAN is it a PITA to get to the gauge back in a COE! Is there any other suggestions or causes of an unsteady reading?? Oh, and I could live with a 'gauge stick' if the COE didn't have a 45-deg bend in it's filler neck. :/

06-07-2017, 12:32 AM	#2
Drbrown Senior Member Join Date: Oct 2013 Location: Glens Falls NY Posts: 1,267	Re: '40 Fuel gauge After fiddling with the gauge, you've gone after the obvious, the send unit. OE senders are getting hard to find. Have you removed the sender unit and held it horizontal while slowly raising and lowering the sender arm while watching gauge ? You can do that sitting in the cab by using some jumper wires. Try lightly spraying the interior parts of the sensor with electronic cleaner. If you get any kind of a reading on the gauge I suspect that at least there's no "break" in the interior sensor. Otherwise, sitting in the cab with the sender using a pair of jumper wires (ground and sender connection) connected direct to gauge terminals would indicate if you you had loose or faulty wiring between the gauge and tank. Try substituting the gauge with one known to work. I have a spare stock mid-1940's you could borrow (mail back and forth ?). The gauge internal part may even be interchangeable with yours. Note: After the "fix" is found/complete, use a gas-compatible sealant on your sender unit gasket (not all are) when installing it.

06-07-2017, 05:21 PM	#3
WQ59B Member Join Date: May 2014 Location: NJ Posts: 69	Re: '40 Fuel gauge Sponsored Links (Register now to hide all advertisements) I don't have a known good one, only have 2 & 1 is 'known bad'. All wiring is brand new. Will look at testing it as you stated... I did try the sender on a known good oil pressure gauge, to see if the float arm moved that needle, and it did. Don't know why this assembly is causing the needle wavering. I read a bunch of threads where folk here recommended cork for the tank gasket. I have rubber there but when I took the sender out last week, it did look whitened with some cracking. Going to replace that with cork... or can I use gasket paper?