Fuel System: OHM range on fuel sending unit - 1937 Dictator model

[Ausstude]

Is anyone able to help me please with the OHM range on the original fuel sending units fitted on 1937 Dictator models ? Thanks.

[gordr]

Is it a one-wire unit, or a two-wire unit? Six volt single wire units in later years were about 20 to 150 ohms. I think the resistance was similar in the two-wire units, but it was obviously connected differently. In both, the moving contact (wiper) is connected to ground. In the single-wire unit, one end of the resistance strip connects to the gauge unit, and the other floats. In the two-wire unit, each end of the resistance unit is brought out to a terminal that goes to the gauge. I have a two-wire sending unit hanging on the wall of my garage, and I can check it in the morning.

[Ausstude]

Thank you Gord. I don't have the original sending unit unfortunately. I am thinking of getting a different fuel tank and essentially wanting to know what type of sending unit will be most suitable to fit to my guage.
Regards, Peter

[5brown1]

0-30 ohms although you cannot find that information anywhere it seems.

I am editing this as I believe it is actually 0-90 at least 38 gauges are that I have tested.

[gordr]

I have yet to go out and check the resistance of the '40 sending unit I have. AKAIK, one cannot use a single-wire sending unit to actuate a two-wire gauge. The two-wire sending units were in use on some models as late as early 2R trucks. I know that because I have seen them. There was a period when both were used.

Now, it might be possible to open up the gauge cluster, remove the guts of the fuel gauge, and substitute the guts of a later model gauge of the same design family. I was able to put the guts of a 12 volt lark gauge into a 2R cluster quite easily.

I have a '38 Commander here, but it is half-buried in a snow bank, so I won't be getting near the fuel tank any time soon.

[gordr]

Just checked the sending unit from the '40 Champion: 22.5 ohms, stud to stud, and the wiper is grounded. The resistance element is tapered, as it is in the single-wire senders, probably to compensate for the fact that the float moves through an arc. If the resistance element were linear, then delta R would be proportional to delta Theta (Theta being the angle of the float arm from one end). Making the element tapered corrects for that, so that delta R is more or less proportional to delta L, "L" being the level of fuel in the tank.

Now some prior owner of the car had the sending unit apart and worked on it, but there's no indication of any wire having been removed from the resistance element, or of the whole element being replaced. And it still hangs up. Looks like the wiper spring is snagging on the fiber back board to the resistance element. A little tweaking with tiny needle-nose pliers may fix it.

Peter, if you could get the instrument cluster out of the dash, and the fuel gauge unit out of the cluster and post a photo here, I, or others here might be able to recognize it as being similar to some other model, and be able to recommend, or source a "will fit" that would work with a more readily available six-volt sender (or 12 volt, if you were to make that choice). Or perhaps one of our vendors will have an NOS '37 sending unit. I am pretty confident that yours will prove to be a two-terminal device, but not certain of it. The gauge that goes with the two-terminal sending unit will have three terminals: IGN, two to the sender. The fourth is ground, but I don't think it exists as a terminal stud; just the gauge backplate.

[Ausstude]

Thanks you Gord and Steve. That's all very useful information. I will have a better look at the guage and see what I can find out. The gauges are currently out of the car but I haven't even tested to see whether or not they are working.
Cheers, Peter

[gordr]

Upon further examination of the '40 sender, a prior owner did mess with the resistance element. It has been sort of shakily rewound, and the winding coated with epoxy. I suspect the original 30-ohm winding broke, and someone redistributed the remaining wire over the whole form. I reassembled it, and it kinda-sorta works. I will try it in the tank, eventually. So I would suggest the 30-ohm figure is correct.

[Ausstude]

Thanks again Gord, that's great.
Cheers, Peter

[rkapteyn]

http://www.mykmlifestyle.com/KM_Lifestyle_Fuel_Senders.html

These people have been helpful.
In 1938 there was a new standard (SAE 5) for the mounting flange of the fuel senders.Some early 1938 Studebakers still used the larger flanges that Studebaker used on previous years but than switched to the standard size of flanges used by all American makes.

[Ausstude]

Thanks very much, I will check them out.

[ddub]

http://www.mykmlifestyle.com/KM_Life...l_Senders.html
These people have been helpful.
In 1938 there was a new standard (SAE 5) for the mounting flange of the fuel senders.Some early 1938 Studebakers still used the larger flanges that Studebaker used on previous years but than switched to the standard size of flanges used by all American makes.

Interesting that the above website has no Stude application for 49 - 55.

[Jerry Forrester]

Interesting that the above website has no Stude application for 49 - 55.

I saw that too. And was befuddled by it.

[rkapteyn]

Interesting that the above website has no Stude application for 49 - 55.

SI carries those

[GWCagle]

When I restored my car I had a good gauge but a bad sending unit. I used resisters from Radio Shack to test the full and empty settings on the gauge and found that 100 ohm was empty and 0 ohm was full. JC Whitney used to sell generic sending units, and I bought one that was 10 - 90. I reversed the board on the sender, making it a 90 - 10 and it worked well for years. Since I needed a 100 - 0, the gauge would read a little above empty when it was really empty, and a little less than full when full. I believe that a 240Z or B210 Datsun also used a 100 - 0 sending and I will try one of them next time I need one.