1955 fuel gauge sender

[rick55]

I have just fitted a replacement fuel gauge sender to my 55 Ford Customline and are wondering abouf the experience of others. The unit i bought was the unit Dennis Carpenter sells which is for 36- 55 Fords 6 and 12volt. I have converted the car to 12volt and am using a solid state voltage reducer for the gauges. I have reversed the polarity of the gauges by swapping the connections on the back of ghe gauge. My question is that the gauge takes some time to register and even with a full tank doesnt show more than 3/4. Is this the experience of others.

[Kahuna]

Rick
I think any new sender will require some adjustment to get the right readings. At least that has been my experience
Jim

[rick55]

The procedure for the sender is specific to fuel tank depth. There is no adjustment in the float arm that i can see. The gauge is also very slow to start reading once ignition is turned on.

[Beav]

Sorry for the long post but it's necessary to reflect the information.

The polarity really doesn't mean anything, at least in reference to the stock setup. Regarding your solid state voltage regulator, well... that might make a difference depending if it can work with reverse polarity. Swapping the wires on the back of a stock gauge will have absolutely no effect.



The gauge works by current heating a bimetallic strip that is connected to the needle. As current flows through the strip it heats up and causes the needle to move as it deflects. In order for the gauge to read correctly and not be affected by voltage and current variances the original sending unit included another bimetallic strip that would click on and off (speed of this action in direct proportion to the current flowing through it) thereby regulating the current and voltage, much like a turn signal flasher. The more current, the more heat and the longer the open time thereby reducing how much current is available at the gauge. The float arm, affected by the fuel level, increased/decreased the position of the point arm thereby altering the duration of time that current was delivered to the gauge and changing the needle position as a result. Now you can see how 6 or 12 volts was inconsequential as it is regulated. Being everything is operated by heating strips, polarity has no more affect than which way a light bulb is connected.

HOWEVER, be very aware of your wiring - I found out my truck's PO made a mistake in his wiring and sent voltage through the sending unit which burned the nichrome-wrapped card. It got hot enough that it melted the plastic the wire was wrapped around. How it never caused an explosion is just luck on his part (maybe even mine, as I drove it from Toledo to Louisville when I bought it.) It must have been submerged in the fuel as I doubt that if it had been that hot in an air-fuel mix it wouldn't have sent one of us on a trip to meet Alice Kramden on the moon.

So... the sending units sold these days do not include the regulator - you have installed one to make up for that. However, the sending units aren't exactly calibrated for us, they're just a kind of a generic make-do/it must be you/it must be your car/etc. product. The resistance coil in the sending unit you have is wound to provide a range of resistance that is close, but not quite close enough, to result in an accurate reading. Using a Kent-Moore instrument gauge tester (J-24538-B) I found the following readings applied to my '53 F-100 (resistance readings verified with a Fluke VOM to all be within 0.1Ω):

Full (needle centered on mark) 18Ω
21Ω
3/4 23Ω
25Ω
1/2 28Ω
32Ω
1/4 35Ω
39Ω
Empty (centered on mark) 43Ω

These readings were taken with the engine idling so as to provide a stable 7.15 volts. I moved to the settings both up and down and from 1/8 spans and 1/2 spans to reach the readings. I've measured both "Must be used with original gauges ONLY" style sending units (standard nichrome wrapped and 'electronic'.) Both measured identically (I wish I had written the measurements down but they were in the 22-98Ω range as my memory recalls.) The spec sheet included with the tester shows Ford fuel units to spec at 10-76Ω but make no mention of years or K-S or CVR type units. My truck has had the dash harness replaced by PO and I've installed a new ground to frame wire. I have the stock (replacement) running board tank ('53) and it measures 11" deep. I made the specific arm length adjustments as directed (DC 'electronic' version sending unit) and ended up exactly in the same place I was with the 'standard' replacement unit. I sped up the engine RPM to allow for 7.56 volts and measured about an 1/8 difference in gauge range as a result. Realizing that the missing regulator in the original sending unit is the reason for the gauge inaccuracy I purchased some adjustable electronic regulators on Amazon for ~$6.

I haven't yet had the chance to install one and report back what voltage and, if necessary, re-adjustment to the float arm was necessary to make it all come together. However, I'm scheduled off next week and, weather permitting, it's on my short list of things to do.

[junkyardjeff]

Did you buy one for 6 or 12 volt?,I picked up a 12 volt sending unit for my 55 but it would never read right so I got one for a 6 volt and much better.

[Daves55Sedan]

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Rick, if you are using this in that Australian Customline UTE, I believe that it uses the wagon gas tank. Although the sending unit for the car models will mount on the wagon gas tank, the float arm for the wagon is much shorter than the one in the cars, due to the shallower depth of the wagon gas tank. Decreasing the length of the float arm will increase the amount of travel that the arm will move from full to empty. Try to duplicate the arm length by measuring the original sending arm. It will definitely help, however, these modern sending units are not very compatible with the old gauges.

[rick55]

Thanks for the replies. What you have all said makes sense to me. The sender is fitted to my 55 Customline Tudor Sedan. I've had no experience with the 55s before this car. My other cars were/are Aust 58 car and ute which are 12 volt and use standard Smiths 12 volt gauges. From what you have said it would be normal for the fuel gauge to be slow coming up to register.
The sender I am using is a Dennis carpenter unit of the correct resistance values that states it is for all fords up to 1955 regardless whether they are 6 or 12volt - so I assume they must have internal electronic voltage correction.
I'm beginning to think that my problem must lie with the solid state voltage regulator I am using possibly restricting current flow too much in conjunction with the similar setup in the sender.
I'll try a factory style voltage reducer from from a 57 onwards and see how that goes.
Interestingly I have used a used sender in the past and that gave all sorts of fuel levels none of which were right . It could read anywhere at any time whether the tank was full or empty and yes I ran out of fuel a few times.

[Daves55Sedan]

Rick, I am pretty sure that those reproduced 1957 voltage regulators are also solid state. They just look like the original unit on the outside.

[rick55]

I might as well stick with regulator ive got.
The other part of my question was the delay before the gauge starts to work. It takes probably 2 minutes before it registers as far as it will go when the tank is full. Is this normal.

[dmsfrr]

Originally Posted by rick55

I might as well stick with regulator ive got.
The other part of my question was the delay before the gauge starts to work. It takes probably 2 minutes before it registers as far as it will go when the tank is full. Is this normal.

Go back to Beav's comment #4 again. Especially the paragraph directly under the diagram.

If I'm reading it right your '2 minute delay' may be caused by the voltage regulator you're using making the voltage too low to let the bi-metalic strips warm up in a 'normal' amount of time. At least that's my first guess.

[Beav]

Weather's been sloppy around here the past few days. With any luck tomorrow and Sunday supposed to be better. If so I'll get to work and let you know what I find out.

[Daves55Sedan]

Ummm...here's some food for thought. I have a '55 Courier that I converted to 12 volts. I used a '56 fuel guage and swapped out the faceplate with the '55 faceplate. I used an original '56 sending unit but I had to get it rebuilt. I did not use the voltage reducer ahead of the power circuit for the fuel guage (as the '56 guage and sending unit originally did not have it) and I did not reverse the polarity. So basically, I duplicated the factory installation for a '56 model.
Some one told me (after the fact) that I wasted my time getting a '56 guage and swapping out the faceplate because allegedly, the '55 & '56 gauges are identical in every way). If that is true (I am not sure, please check) then maybe you don't need the voltage reducer at all.
To answer your question, NO. The guage should begin to register immediately upon turning the ignition key to on.

[Dominic Hide]

'55 and '56 gauges are very different and are NOT interchangeable.
All pre 1956 gauges are 11 ohms resistance.
All post 1956 gauges are 14 ohms resistance.
The 1956 gauge has 40 ohms resistance and will ONLY work with correct original style sender.
These values are true for all gauges, fuel and temp, also oil pressure where fitted. (Mercury and flathead)

[Beav]

Isn't '56 the one and only year Ford used actual 12 volt gauges? Before and after '56 they used voltage reduction, at least on the trucks, I believe.

[dmsfrr]

Originally Posted by Beav

Isn't '56 the one and only year Ford used actual 12 volt gauges? Before and after '56 they used voltage reduction, at least on the trucks, I believe.

I believe you are correct, the '55/'57 T-Birds were originally set up this way too.

'55 (and earlier) gauges were for 6v electrical systems, '56 were actual 12v gauges.
The '57 and newer gauges were labeled "12v" but are actually lower voltage gauges for use in a 12v system with a special voltage dropping regulator in the dashboard just for the gauges.

> edit <
Just in case...
double check your battery ground cable to the engine block AND...
that you have a good clean ground wire from the engine to the body of the car.


.

[Daves55Sedan]

Originally Posted by dmsfrr

The '57 and newer gauges were labeled "12v" but are actually lower voltage gauges for use in a 12v system with a special voltage dropping regulator in the dashboard just for the gauges.

Yes! But my understanding (correct me if I am wrong) of the little constant voltage regulator is that it just has a set of contacts that flutter when voltage is applied and that it is not really a 6-volt resistor, rather a "buffer". If that's true, isn't his 6-volt guage overloaded?

[Daves55Sedan]

Originally Posted by dmsfrr

Just in case...
double check your battery ground cable to the engine block AND...
that you have a good clean ground wire from the engine to the body of the car.

I don't know how they originally obtained ground at the gas tank, since it was originally isolated from the body by rubber pads between the trunk floor and top of the gas tank. And the gas tank straps also have rubber pads, so they insulate the tank from ground.

I ran an extra ground wire from the firewall grounding screw all the way back to the gas tank sending unit and put a ring tongue terminal on it and bolted it directly down to one of the sending unit mounting screws. I tapped that ground wire at the first taillight and connected another wire to ground the tail lamp and backup lamp sockets so that I would never have ground issues with the lights back there also.

[dmsfrr]

Originally Posted by Daves55Sedan

Yes! But my understanding (correct me if I am wrong) of the little constant voltage regulator is that it just has a set of contacts that flutter when voltage is applied and that it is not really a 6-volt resistor, rather a "buffer". If that's true, isn't his 6-volt guage overloaded?

I believe your understanding of the dash gauge regulator is correct, it 'flutters'. It's a high speed electronic switch that opens at a pre-determined limit then continues to open & close to maintain that limit.

Here's why I think the gauge seems to work correctly but takes too long to reach it's level after turning the key on.
The fuel sender in the tank works about the same way as the little dash gauge regulator, it flutters, but slower, to control the electricity thru the fuel gauge.
The fuel gauge needle is linked to a heated strip of metal... (refer back to the paragraph directly under the diagram in Beav's comment #4)
and the 'flutter' rate of the temp sensitive contacts in the sender self-limits the electricity passing thru the gauge. It's also why they should be a matching model year *pair*, the oem '55, '56 & '57 gauges & senders are made to different electrical specs.

I suspect having the dash gauge regulator also in the circuit is reducing the voltage/current a bit too much to allow the fuel gauge to 'warm up' to it's eventual reading in a normal amount of time.

Originally Posted by Daves55Sedan

I don't know how they originally obtained ground at the gas tank, since it was originally isolated from the body by rubber pads between the trunk floor and top of the gas tank. And the gas tank straps also have rubber pads, so they insulate the tank from ground.

I ran an extra ground wire from the firewall grounding screw all the way back to the gas tank sending unit and put a ring tongue terminal on it and bolted it directly down to one of the sending unit mounting screws. I tapped that ground wire at the first taillight and connected another wire to ground the tail lamp and backup lamp sockets so that I would never have ground issues with the lights back there also.

The original fuel tank ground? I don't know either. When I replaced my 55's tank there was nothing to see of how it was grounded except for the worn out & missing cushion strips.
Maybe it was thru the steel fuel line from the tank to the frame, but that seems like a suspiciously bad idea to me.
Installing an actual ground wire from the sender flange to the car body is a much better solution, and is on my to-do list. A previous owner spliced a rubber hose into the steel line out of the tank.

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[Daves55Sedan]

Originally Posted by dmsfrr

I suspect having the dash gauge regulator also in the circuit is reducing the voltage/current a bit too much to allow the fuel gauge to 'warm up' in a normal amount of time.

By golly, I think you're on to something here. But if he disconnects the constant voltage regulator from the fuel guage and runs a separate wire from the coil terminal of the start switch to feed the guage it means there will be 12 volts connected to a 6 volt guage. Won't it read double the actual amount of fuel?

Originally Posted by dmsfrr

Maybe it was thru the steel fuel line from the tank to the frame, but that seems like a suspiciously bad idea to me.

I think you've hit the nail on the head! It must be grounded via the fuel line connected to the car frame by those little push-in clips. I pondered like you wouldn't believe how it worked, but never thought of the fuel line!

[dmsfrr]

Originally Posted by Daves55Sedan

But if he disconnects the constant voltage regulator from the fuel guage ..... it means there will be 12 volts connected to a 6 volt guage. Won't it read double the actual amount of fuel?

No, because... the fuel gauge doesn't directly read voltage in the circuit. If it did it would swing between full & empty anytime the car was moving.
Instead it reads the heat in the gauge with it's circuit thru the sender, which is switched on & off by the contacts in the sender at a rate that corresponds with the fuel level in the tank.
In theory.... the increased voltage thru the gauge and sender is self-compensating by the temp/current sensitive contacts in the sender.

Originally Posted by rick55

I have converted the car to 12volt and am using a solid state voltage reducer for the gauges. I have reversed the polarity of the gauges by swapping the connections on the back of ghe gauge.

"You do not need to change any switches or gauges. The fuel and temp gauges will work on 6 or 12 V and are not polarity sensitive."
https://www.ctci.org/gilsgarage/6to12.php

I wish I'd found that link a while ago
It's a concise description of what does / does not need to be changed to update 6v cars to 12v,
and why.


Disclaimer: I've only (barely) dealt with this problem once.
My 55's fuel gauge would only show 3/4 full no matter the tank level, the tank was rusting thru and the sender didn't look much better. I replaced the tank and gauge sender pair with a reproduction set from Casco, and the car isn't back together yet.


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