Gas Tank Sending Unit Woes - 46 Merc

[Curt in AZ]

JSeery, I'll have the truck back on the road in about six weeks and will post the results.

[koates]

The main problem with new reproduction fuel tanks and sender units is that they are made for the HOT ROD and RESTO ROD market and not for original or restored cars. Ask a vendor or hot rod shop if they are suitable for your 1939 original Ford and they will say "sure are", when in fact they would not have a clue. All these rebuilt/modified cars have 12 volt systems and various modern gauges fitted. This subject has been repeated and repeated to the point where I would have thought all old Ford guys knew about it. Ford King Seeley gauges need King Seeley matching sender units to work correctly and accurately and that's it. If your modern resistor type sender unit is working fairly well with an original Ford gauge then that's a fluke of nature. Regards, Kevin.

[psogden]

Guess what? It's "well-----" as can be seen in the pic of my old sending unit. No hope here.

[psogden]

Kevin, Your words of wisdom make a lot of sense. I confess I haven't kept up on this. But, if you have a bad original sending unit and you want to keep your stock gauge, you're pretty much out of luck unless you can find a NOS sending unit, huh? Maybe I really will have to revert to the stick in the filler nozzle approach to know my gas level because I am committed to a stock dash & gauges in my car. I understand why folks are into modifications which make their cars more roadworthy and I understand the whole hot rod thing, but it is too bad that purists are in the minority and after market parts are not made with them in mind. It's the old supply and demand thing, I guess. And there is greater demand for new, jazzy 12 volt gauges so that's where the money goes. Familiar story.

[deuce_roadster]

Hey psogden, as grungy as that looks, if you can gently clean that up, and if the lever moves, pop the cap off the top. You will be amazed at how clean and nice it looks inside. Maybe all it needs is freeing up and a new float. If you take the cap off the top, pull some paper or very (2000) fine grit wet/dry paper through the tiny points and it probably will work fine.
If there is a hole in the bellows part then it is junk, as you need to keep the points away from the fuel fumes.

[rotorwrench]

Sponsored Links (Register now to hide all advertisements)

Most of that crud is old dried fuel residue (varnish). The new reproduction floats are available and fit well into the clip part of the float rod. The float wire looks like it will clean up. The diaphragm can looks to be in good condition where the float float rod makes contact to it. I've seen worse repaired before. I'd pop the cap and look at the condition of the breaker/heater mechanism and wire spool (calibration wire). It may just need the little breaker points cleaned as was mentioned.

[allout]

Do what deuce roadster says. Mine looked way worse then that when pulled. I cleaned it up and put a new float on it and it works pretty good. It is not perfect but is accurate at full and empty, sometimes around half a tank it will fluctuate a bit but then steadies out again at 1/4. Good luck.

[Paul Bennett]

Don't recall how many tens of cars I've owned but NONE has had an accurate gas gauge. So ignore the purist nay-sayers.

The singular purpose of a gas gauge is so you avoid inopportune running out of gas. And a resistance gauge can do that. But I suggest a dry run outside the tank before installing the sender. It is easy to bend the float rod to accomplish what you want for a full or empty reading to be.

[psogden]

I appreciate everybody's encouragement. Will take a 2nd look at this.

[psogden]

I appreciate the words of those who felt this unit might be salvaged. I followed suggestions to clean the unit. Here are some "after" photos. I was really surprised how well this unit cleaned up and the arm moves very freely. The part number is visible on one of the photos. I guess the next step is ti pry the top off and do the things that were suggested-- or not? Do I need to do that? How can I tell if the unit will work (before I install it)? Thanks. Hanging on to hope.

[JSeery]

I would start by connecting an ohm meter and see if you can detect the contact points opening and closing as you move the arm through empty to full range.

[rotorwrench]

It can be connected to the vehicles gauge send wire with jumper leads and the body to a common ground for a test of the whole system as long as the vehicles electrical system is up to par. With the cap off you can rig it to watch the points open and close but you have to take care not to short anything out.

[psogden]

OK will give it a try. Thanks.

[19Fordy]

psogden: Here's what the inside of the sending unit looks like and how it operates.

An easy way to check it is to disconnect the wire from the unit and then cover the open gas tank with a rag to subdue fumes.
Then lay a piece of cardboard on your trunk floor, place the sending unit on top of the cardboard and with the ignition OFF reconnect the wire the wire from the gauge to the top of the unit. Then connect a wire from the edge of the lip of the unit where the screw holes are and run that wire to a good ground like floor trunk latch. Now turn on the ignition and move the float arm through its travel and visually look at the fuel gauge. Use alligator clips to make this easier. Make adjustments by bending the little metal tab which controls the range of motion of the float or by bending the float arm or both.
The little star wheel inside the unit can also be moved but only as a last resort. If you do move it, move it microscopic amounts. Plus make sure the little carbon "resistor ?" in the unit is seated. DON'T BREAK IT.

[Brendan]

i just get gas every 100 miles

[Paul Bennett]

Originally Posted by Brendan

i just get gas every 100 miles

Try Tums

[psogden]

Finally got around to testing my cleaned up original sending unit manually (out of tank). It moved my gas gauge from empty to full settings as I moved the float wire back and forth. Good news, right? Wrong. The original sending unit will not fit on the new tank I purchased--2 reasons. First, there is about a 1/16" lip around the opening on the new tank (vs. the original tank which is flat). Second, the opening on the new tank is a tiny bit smaller in diameter than the original. As a result the original sending unit will not fit on the after market tank--no ifs, ands or buts. It might possibly be made to fit if the lip was ground down--but then I'd have grindings to remove from the tank--wouldn't be a smart idea. Or, if I built the gasket up to about 1/4" thickness, I could get by--but this would result in inaccurate readings.

I then did a manual test on the Drake sending unit. It also moved my gas gauge from empty to full. My conclusion is that the Drake unit may not be as accurate as the original Ford part but it will tell me with reasonable accuracy how much fuel is in my tank--and if I never let the level drop below 1/4 full I should be OK. So, after all that, I will go with the Drake sending unit. Too bad the manufactures of these new tanks don't make them to the exact Ford specs. Would be nice to know ahead of time.

Thanks again to all of you who took time to reply to my posts.

[JSeery]

I would modify (grind) the opening to fit the original sender. If you go with the Drake sender keep us posted on how it works once installed.

[psogden]

I will let you all know how the Drake unit works. I'm not up to removing grindings from a new tank after grinding down the lip. Suppose it could be done by flushing with water & letting dry out before I install--but don't think I will do that. Thanks again for the responses.

[FRANK PKNY]

I had a repro unit in my 39 PU only lasted 6 months and fizzled out. I have yet to repair it because getting at the unit i must remove the tank. I did find a used one at a V8 meet and purchased it it was old looking and kinda crusty. So I grounded it to my truck and ran a wire from the gauge to it and walla it works perfectly. Now to remove the tank and put the old one in is on my things to do list!