Gas Gauge drops to empty fast.

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'73 Root Beer

'73 Root Beer

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New sending unit. Old one when I bought car had hole in the float. Fill tank gauge reads full, 100 miles 6.5 gallons of gas later I am on E. Sending unit need calibrated? I was told it was at 78 at empty and 2.5 ohms at full. Ground at dash? New grounds at sending unit.

1973 Swinger 16 gallon tank.

Thanks
 
This is one of those times when a 100 ohm high wattage potentiometer and Ohm meter are handy. There are many ways to test. The gauge is slow, so a couple minutes is required after changes in resistance. You can get by without the potentiometer if you test using sender prior to install.

To save work it is often good to test first. And when installing unit make sure the float drop works correctly. Not sure of the stock resistance specs. They have been posted before by 67dart273.
 
Should be 10 Ohms at full
2.5 Ohms will fry the gauge eventually.
That gauge was probably about shot anyway. It is 40 yrs old afterall.
 
With 2.5 Ohms it seems the tank would read full longer than expected. I also agree the gauge could be damaged.

It might be possible to limit travels in the sender and modify the float arm for correct tank float swings. At the same time the gauge must be verified that it works correctly. Much work involved.
 
The picture of the two senders is worth 1000 words. Without significant modification it is unlikely it will work correctly.
 
KitCarlson said:
The picture of the two senders is worth 1000 words. Without significant modification it is unlikely it will work correctly.
Click to expand...

Either sender works the same. Different lengths of the float arm is not a factor. The long sender was the original design. Its flaw was allowing the float to bounce against the bottom of the tank. They either got a hole in the float or so much slosh motion wore out the moving contact. That contact would take on a hook shape and catch/snag on the ristance winding, thus a hung sender.
The later shorter sender with several bends is much more rigid. The only flaw with that sender design is trash collecting at the bottom of the radiused contact housing. Eventually that area is covered and blocked. Then the gauge sits at some where just above empty while you run out of gas.
 
I might be off do to perspective. Seems to me that if the sensor angle travel is reduced by adding end stops, then the float rod length would need to longer. With the rod as short as it seems it may not be able to reach top and bottom.
 
I just bought a new spectre unit and its doing the same exact thing. Only two good things about it is that when you reach empty-you still have almost half a tank of gas left-no rushing to a gas station, and- when you do get to a gas station- it only takes $30 to fill it lol.
 
I went the other way new 16 gallon tank and sender. added 4 gallons and bent the arm (a lot) till it read 1/4 tank! Now it reads full a long time.
But in hindsight - I would have adjusted it to read an 1/8 with 4 gallons. FYI 4 gallons is just below the bottom of the hole for the sending unit
 
Well I know my mileage as the sending unit was bad when I bought it. Went a month W/O a gauge. Going to adjust ohms on sender and if still same try new gauge. Not the end of the world. Thanks all!
 
I seem to remember a post about someone inserting a camera in the fill opening on a new tank and sender installation. He then did work for internal electric pump install and tweaked the sensor assembly to work correctly. The camera let him see to adjust float drop and pickup position.
 
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