Gas Tank Sending Unit Woes - 46 Merc

[psogden]

In order to get the 10-32 screw holes on my new sending unit to line up with those on the tank, I had to partially re-drill 5 of the 6 holes on the mounting plate. The holes on the neoprene gasket lined up perfectly with the tank but not so the holes on the plate. Wonder how the manufacturer could have missed it so badly. Buyers beware!

[JSeery]

Your going to have bigger problems than that! These senders are not very compatible with the original gauges and it is difficult (and sometimes next to impossible) to get them to read anywhere near correct.

[Kahuna]

J is exactly right. These tend to be very problematic

[psogden]

I appreciate the warning. The vendor specifically stated that the sending unit is intended for use with original Ford gauges. The next best option, I suppose, is to reinstall my original 60 year old unit which was working when I removed the old tank. Other than that, I guess I can go to the wooden slat down the filler tube method--kind of like a dip stick approach. Any other ideas?

[rotorwrench]

A lot of these repro tanks have a sender unit bung made for more modern type sending units. I've also seen adapters made to use a different sender but I don't know what was adapted to what on those applications. I still just try to find the OEM stuff which can be difficult now days.

[hotrodart]

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I have one in my '40 sold by Drake.....do not know where he gets them, but it works well with no issues.

[lfson]

Ordered a new tank for my 47 Merc from Drake when he introduced it at the Lake Tahoe meet in 2013. Half a year later when it arrived, and I intended to install it I noticed the original sender didn't fit - no way. Had to order his sender. With the tank full it required som bending of the arm to get the guage to show full. It works OK.

[Floyd]

If your "old" one was working, reinstall it and it will be accurate and probably last forever. There is really no other option. Most of the old senders are still good. However many people think they should buy a new one. Problem is there is no such thing as a new one because King Seeley does not make them any more.
One thing you should check is the condition of the float as many of the old brass ones develops tiny cracks and therefore leaked. That would make for an inaccurate reading at the gauge.
Just my opinion

[rotorwrench]

I just wish they would offer a new tank to accept the OEM parts. Nothing like taking a new tank and installing a crap sender just because that's all they want to make. I've thrown away more bad resistance type fuel senders than I care to count over the years. Those King Seeley units were the best product ever made for that purpose that I've ever had the pleasure of maintaining.

[fordor41]

I installed a sender in my '41 from Yogi's that is matched to my stock gauge. works great

[rotorwrench]

You can get one to give you a reading but they are just not compatible units. There is no way that a resistance unit can be made to work through the whole range. Yogi's stuff is pretty much the same as every other unit out there.

[JSeery]

These resistance units may "work" to some extent, but they will not work properly. If the users are happy with them, that is great. But just realize there is no way it can really send an accurate signal to the gauge, the original systems used totally different technology. It would be very interesting to see what some uses consider working well. It would be possible to get a resistance sender to get the gauge to read near correct at a few data points.

[deuce_roadster]

Like Jseery mentioned, the original sender and gauge operated on a FREQUENCY signal not voltage. The sender in the tank has a set of points that the gap gets changed by the float moving up and down. The gauge, is calibrated to read this FREQUENCY change and display accordingly. This is why a modern sender that is simply a voltage to ground signal will give readings that are not really accurate. I believe King Seely had a patent on this.

[Kube]

Originally Posted by deuce_roadster

Like Jseery mentioned, the original sender and gauge operated on a FREQUENCY signal not voltage. The sender in the tank has a set of points that the gap gets changed by the float moving up and down. The gauge, is calibrated to read this FREQUENCY change and display accordingly. This is why a modern sender that is simply a voltage to ground signal will give readings that are not really accurate. I believe King Seely had a patent on this.

From my experience the repop sending units are poopy. I have been buying every NOS unit I can get my hands on in the past few years.
Yeah, the repop units work "okay" but if you drive your car and are counting on an accurate reading, well, "okay" I'd think to not be good enough.
Or, if you are like me and expect things to operate as they should, then these units simply will not work.

[JSeery]

This seems to be a very frequent topic, wonder how difficult it would be to reproduce the King Seely units? Or a modern equivalent that would reproduce the original output.

[rotorwrench]

It could be done if someone tooled up for it. Plastic would be out of the picture due to the heating element so metal would be a must. The hardest part to fabricate in my way of thinking would be the diaphragm used to apply pressure to the bi metallic strip. It has to be sealed to keep the electrical parts from the fuel. It was crimped kind of like a miniature soup can.

It would be easier to repair a decent one than make a new one. That way a person would likely only have to reproduce a few small internal parts. Still not easy but much easier than making the whole thing.

[deuce_roadster]

I think in the service notes, it tells you if you apply exactly 1.5 volts to the gauge, the needle should come up to a mark on the bottom part of the gauge dial that is somewhere near 1/2 if I remember right (getting harder to do!). There is an adjustment in the gauge to set this. Then you connect the sender to the gauge and with power and grounds it will go to Full when the float lever is up and go to Empty when the lever is at the lower end of its travel. There are adjustments on that too by bending tabs.
The original units are very accurate.
One of our club members is very good at calibrating these units together so when the gauge is at Empty, you have 1 gallon of gas left.

[Curt in AZ]

I used a reostat to set my aftermarket unit to match the gauge at empty. The tank is still out of the truck so don't know what it will read when the tank is full, but that's less of a concern to me than having an accurate MT reading.

I connected a large reostat in place of the sender then slowly adjusted until gauge pointed at the empty mark. Then disconnected the reostat and read the ohms across it. Then bent the float rod to match the measured restance when the float is resting on the tank bottom. I'm now thinking to redo it 1/2" above the bottom.

The reostat is inexpensive (https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1) and durable.

[JSeery]

Be interesting to see how it works out Curt. Yes, the resistance from the modern sender will match the current flow required by the gauge at specific points, however it will not provide the correct curve from full to empty. With enough trial and error (or measuring in your case) you may be able to get full and empty close enough.

[psogden]

Lots of wisdom from all of you. Appreciate it. Obviously no one "right answer" but if the original (old) one will fit on the new tank, I'll probably run with that. If not, well----.