1940 Ford fuel gauge issue

[Automotive Stud]

I'm having issues with the fuel gauge not reading correctly on my '40. It's converted to 12v, but it has a Mustang style voltage reducer feeding the fuel gauge. If I ground the sending unit wire it reads full, so I thought the sender had failed. I bought a reproduction Vintique 6v sender since I'm still using the original gauge, but on a full tank it still only reads about half full. Any ideas on what's going on here?

[JSeery]

I would try and go back to the original sending unit if possible, the resistance unit will be difficult to get to work (they can be made to work after a fashion, but not easy). Grounding the sending unit wire should give you a full reading on the gauge, so that seems to be working ok. Might try grounding one of the sending unit mounting bolts to a know good ground.

What the original sending unit is doing is opening and closing a set of point that is related to the amount of pressure applied by float. So if the extra ground doesn't help, check and see if the float is working correctly. If that is not the issue, you may need to open it up and see if the points need cleaned.

[hotrodart]

I have a similar issue on my '40 coupe......stock gauge/resistor with aftermarket sender. I am told the aftermarket senders operate on a different principle and cannot ever be accurate. Best bet is to find an original sender, or fix the one you have.

[19Fordy]

Wouldn't it be nice if someone would make a stock looking 12V 40 Ford fuel gauge to operate with the aftermarket 12V repro. sending units?

[Hal Beatty]

Or reproduction K-S sending units...

[Automotive Stud]

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This is the sender I used, thinking it would be fine with the stock gauge.
https://www.vintagepartsclub.com/for...ket-1935-1948/

What's involved in getting to the contacts in the stock sender? I already replaced the float because it was sunk, but it still didn't read properly so I bought this. Maybe I should revisit fixing the original.

[deuce_roadster]

All the KS 6v sending units are the same up to I think 56 or whenever they went to 12 v. The rod the float goes on is different for different tanks. There are also stops you bend to adjust the travel of the float arm. Most of those sending units can be cleaned up and work fine. I have a FOMOCO kit that is a replacement that has a chart which shows how to adjust the arm for different models and I can send a copy of the chart to you if you PM me your email address.

[tubman]

I was able to fix an oil pressure sender for a King-Seely gauge. It involved cleaning it up and dressing the points. It worked fine afterwards. The hard part was getting it apart, as they were designed not to be repairable. I got it apart and back together satisfactorily, but it looked pretty ugly when I was done. Since you can't see the gas gauge sending unit, looks are not so important.

There was also a "star wheel" adjustment on the oil sender.

[JayChicago]

I don't think we know that his first sender is an original King-Seely. That sender could be another aftermarket resistance unit installed by a previous owner, which explains inaccurate gauge readings in the first instance.

[19Fordy]

This may help.
https://www.fordbarn.com/forum/showt...k+sending+unit

and
https://www.fordbarn.com/forum/showt...ng+unit&page=2

[fordor41]

I used a stock fuel gauge, Ron Francis voltage reducer (VR-1 12-6V) and a sender from Yogis street rod parts 73-10 ohm. E was empty, F was full. In between who cares

[JSeery]

Originally Posted by fordor41

I used a stock fuel gauge, Ron Francis voltage reducer (VR-1 12-6V) and a sender from Yogis street rod parts 73-10 ohm. E was empty, F was full. In between who cares

Great if you can get it to work, a lot of people have trouble getting the resistance units to work correctly.

[Charles Brock]

I’m running 12 volts in a’40 with original gas gauge with a Ron Francis VR-1 reducer and a Bob Drake sending unit. The original gauge reads perfectly.

[Automotive Stud]

I'll bump this back up with some more information. The car is 12v, but I'm using a Mustang instrument cluster voltage reducer like this to power the fuel gauge. When I ground the wire that goes on the sending unit to the trunk floor the gauge reads full, but it barely works at all with either the Vintique sending unit or the original with a new float.

I tested the new and the repop sending unit with an ohm meter and got similar readings, so I think both senders should be in working order. I tried grounding the gas tank better but that didn't make any difference.

[jayvee34]

i had the same problem on my 40 Merc sedan. BTW The gauge should read E when grounded, not F. I switched the wires and the gauge worked. My sender was from Bob Drake. With the voltage reducer the needle on the gauge moved slow, but was accurate.

[Automotive Stud]

Originally Posted by jayvee34

i had the same problem on my 40 Merc sedan. BTW The gauge should read E when grounded, not F.

Are you sure about that? The car is negative ground. With the sending wire off it reads E, when grounded it reads F.

[jayvee34]

Originally Posted by Automotive Stud

Are you sure about that? The car is negative ground. With the sending wire off it reads E, when grounded it reads F.

I apologize, if I am wrong, but what I said is exactly the way it went with me.

[Floyd]

The only thing that works correctly (accurately) is original KS sender ,KS gage and 6 volts. These things seldom ever fail if paired together. 12 Volts is wrong. Ohm meter is not useful on original setup as it is NOT a variable resistor. It is variable current opening a set of breaker points from the heating wire.

[Ggmac]

Tell me if what I do is wrong . I have done it dozens of times . Back when junk yards were full of 80s ford products , I would takeas many as the day would allow , just the gauge . I was amazed that ford changed nothing in the gauge , more plastic of course but same looking design . All I did was swap the guts from the 80s ford gauge into the 40s factory gauge brass cup and faceplate , and needle . Then I used a aftermarket ford ohm sender and the factory 1980s cvr ( constant volt reducer ?) . Of course all this was because the original sender was gone or bad .
Havent had an issue, in fact I just did it last week on my new to me 41 .
Have I been lucky or should it just work like it has been . I can send pics of internals comparison to someone .

[fordor41]

Originally Posted by Ggmac

Tell me if what I do is wrong . I have done it dozens of times . Back when junk yards were full of 80s ford products , I would takeas many as the day would allow , just the gauge . I was amazed that ford changed nothing in the gauge , more plastic of course but same looking design . All I did was swap the guts from the 80s ford gauge into the 40s factory gauge brass cup and faceplate , and needle . Then I used a aftermarket ford ohm sender and the factory 1980s cvr ( constant volt reducer ?) . Of course all this was because the original sender was gone or bad .
Havent had an issue, in fact I just did it last week on my new to me 41 .
Have I been lucky or should it just work like it has been . I can send pics of internals comparison to someone .

That's exactly what I did with my '41. I used a Ron Francis VR-1 reducer. I was amazed that the gauge from the 70's Ford truck fit exactly into my '41 gauge housing

[Ggmac]

I now use a modern voltage drop . Good thing I had a coffee can full of gauges , you can hardly find a 80s car in the junk yard .

[Automotive Stud]

Alright so I decided to revisit the stock sending unit. I popped the cap off and looked at the links that 19fordy posted. I see the points and everything appears to be in decent shape, although a little crusty. I noticed before removing the points plate that regardless of the float position the points are contacting each other, they move up and down as a unit. From some of the linked posts that seems correct. My points aren't stuck together. I'm going to try to clean this up, maybe take a point file to the points, and try the adjustment procedure outlined with the star wheel and see if that gives me any satisfaction. When I first got this car on the road the fuel gauge worked for the first tank until the float sunk. I replaced the float on this sending unit but was never able to get it working right again.

[Anteek29]

Bet cleaning the points will get you going again.

[19Fordy]

Be gentle with the sending unit. Do not damage that "carbon resistor" but make sure it's fully contacted. Make sure you float has no hairline cracks. Run a ground wire from the sender to the frame to make sure you have a good ground.

[51woodie]

Auto Stud. Be careful poking around in the sender, as others have cautioned. When I was repairing mine, I somehow lost the little insulating button that is at the end of the copper arm where it rides on the adjustment cam. When it is missing, the sender shorts to ground. It took me a bit to figure out what was wrong, but the pictures I took on disassembly showed the button missing. I had to make a new one out of plastic on the lathe. As well, I used 1000 grit wet paper to clean the contacts. One more tip, disconnect the power to the coil when testing the fuel gauge, or you might/will fry your ignition.

The adjustment "cam" need very little movement to make a difference in the gauge reading.

[47Monarch]

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I got a sender from Joe's Antique auto instructions stated good for 6 or 12 volts. Works ok stays on full for long time when it gets to 1/4 hope I have comfortable walking shoes. I think I messed up cutting the float rod

[19Fordy]

You can easily solder the float rod to make it longer.

[JayChicago]

Originally Posted by 47Monarch

I got a sender from Joe's Antique auto instructions stated good for 6 or 12 volts. Works ok stays on full for long time when it gets to 1/4 hope I have comfortable walking shoes. I think I messed up cutting the float rod

You didn’t necessarily mess up the float rod. That’s how the aftermarket senders act. They will work on our gages, but with no accuracy.

You can add a resister to the wire going to the sender to bring the gauge needle down some. Try about a 7 or 10 ohm resistor. It is trial an error to get it close to accurate when empty. Still won’t be accurate when tank full, but that’s not a problem.