Hey guys. Hoping someone may have some insight into this issue.

72 Barracuda. From what I can tell, stock tank. It had what appeared to be a stock sending unit in it when I got the car, and it was toast.

I bought a new one from Rock Auto....got it and found it didnt read right. Like it would read 1/2 tank when the tank was full. bent the float arm and after numerous trials and errors got it to read right at half and full. But found it had numerous dead spots....the gauge would go to empty for a few miles and then go back to the correct level.

Well, thinking it was a cheap sender I sent it back and bought a "better" one from a well knowm Mopar restoration outlet. The unit had a larger price, about $50 more as I recall....the unit LOOKS to be better quality for sure. Ok, so installed that and found that it read a half tank when the tank was full.

Many more trials and errors , which includes draining the tank to half so I can pull the sender , and I once again have it reading properly at half and full. But this time I find I still have two dead spots...one at half and one at 1/4 tank. I confirmed that it was the sender by running several tanks of fuel through it. Every time, same spots, same results...drops to empty. A few miles later and it goes back up. At least it was predictable.

I brought this to the attention of the vendor and he suggested I return it sinice it wasnt right.

Well, I have the new one in and once again, I have a half tank of fuel in it (8.25 gallons) and the gauge reads just barely off of empty.

Before I go thru yet another round of drains/bending/refills, does anyone have any ideas here?

I have checked the sender out of the tank, hooked up to the wiring/gauge.....when the float is all the way down the gauge (stock dash) read empty.....all the way up, it reads full. Just like it should.

The tank appears to be stock and it does hold just about 16.5 gallons or so.

The ground strap is new....and connected good. I even ran a second ground wire and ran it straight to the battery to see if that would change things....no change at all.

I for the life of me cant understand why I am having this weird issue.

It seems like the sender is the wrong one or something for the tank.

But I have looked and the same sender unit is specified for all years of e body cars.

Anyone? I am at wit's end!

I would check the ohms with it still installed in the tank as is, at the 2 dead spots which would confirm an open in the sending unit windings. I'm wondering if when you mock it up & manually move it thru it's travel that you are holding a bit of side pressure onto the arm as you move it across the windings whereas in the tank it is more free floating and hitting 2 places in the windings that are not flat & hence no contact. but for 2 senders to be acting the same (if I read that right), I agree that does not have a logical explanation but it's gotta be something simple (after we find it) and I wanted to throw something out there to (hopefully)contribute.

Being as it has happened with three different senders, might it be else where? The gauge maybe?
Just a suggestion.

Just as an FYI to add to this issue, I have a B body tank that was stamped wrong, and the angle of the sender is such that the sweep isn't from the bottom to the top of the tank. Very strange. You wouldn't know it, unless you put an angle gauge on the tank...

Have you checked the ground?

I would make sure that all your grounds are connected (engine to frame, frame to body, body to engine). My stock sending unit only worked part of the time, and after it was at a shop and they claimed it was working and it was not, I checked and repaired/replaced all the grounds, and now it works correctly.

Last year I did a little test that included putting in a original factory sending unit to replace a repro which I think is a spectra. Before doing this I ohm tested both units per the factory book and both read within specs well the factory unit read correct when put in the tank and the repro did not. I put the repro back in because I run 3/8 and the factory one I had was 5/16 so until I know of a accurate repro or get a original unit in 3/8 I will live with it I have not tried the bending the arm method yet.

If the sending unit is a one wire unit, there must be a ground strap that goes from the sending unit outlet and connects to the main fuel line.

Jumps over the rubber hose, needed to have a good ground

three senders all wrong? I'd yank that gauge, clean the contacts, check your cluster ground, find an ohm chart, then buy resistors from radio shack and use them to adjust the gauge.

I was thinking of removing the sending unit part of the original pick up and using it on the repro. Have to look about doing some surgery.

But the fact he has plugged in an original sending unit & it works tells me the repo senders have all been bad...

If this were the case he would not have a problem would he? He would have a sender that works right?
He does not, time to look else where. He said that all his grounds are good time to look else where.that leaves wiring and the guage doesn't it?

Yep I could be wrong happened once before I thought I made a mistake but I was wrong.
I agree time to look into the rest of the system.

Just to reiterate what I did:

I tested thecurrent 'better" repop I have as well as the last one outside the tank....hooked up the wire and the ground and tested that way.....the gauge registered full when I raised the arm to full, and measured empty when at rest at the empty end of the swing.

It just seems like the unit itself is calibrated wrong for the tank.....the dead spots are a seperate issue, as once I tweaked the first couple units for the level it seemed ok aside from the dead spots.

In my case the original sender didnt work at all...I did compare it to the first (cheaper) repop and tyhey looked basically the same aside from the repop seeming "cheaper". I have since tossed the original (dumb move). The "better" repop appears to be the same as the cheaper one in terms of measurements.

I am convinced that the gauge itself and ground are fine.

Sounds like your only issue now is the dead-spots?

If that's the case, take both senders out and measure the resistance as you move the arm. The resistance should increase/decrease at a fairly constant rate. As was stated, you'll probably seen a "jump" at a certain point in the travel. Look closely to see if there are any irregularities in the windings/arm at this point.

Maybe your adjustment/bending the arm caused intermittent contact at certain points during its travel.

I can't offer anything of help, but I can say that I'm experiencing the same thing. The first sending unit was way off, so I put another one in. This one too is way off. A full tank of gas reads 1/2 on the gauge. I took that one out and tried bending the float arm. Of course it's still way off. Once the body work gets going this summer I'll pull the tank out and go over it one more time. After that, I'll just deal with it I guess. Not that I go on many long distance road trips anyways I suppose.

I spent some time today once again bending the arm of the latest sender to reflect a half tank of gas.

What a pain.

At least I knew more or less how I needed to bend it this time....

I wont know if I have dead spots for sure until I actually run a full tank now. And I wont know if the full reading is OK or not (before, my bending resulted in a full reading waaay past the usual full mark).

I have tried the ohm;s test/sweeping the arm......I think I mentioned that in the first post.....the last one I detected no dead spots but had them anyways.

it could be that my tweaking induced them as was suggested.

That said, my main concern is why these senders are so off....I mean, showing a empty tank when its half full seems to indicate an issue...after searching a bit, I have found that its (thankfully) not just me.

Some folks seem to have great luck with the senders working the first time....then others have the same issue I am....

So, what is the difference?

All I can figure is there is some difference in the tank itself....maybe the dimensions are off?

Dobie, maybe we can compare notes....what year/model car are you working on?

I dont have any cross country trips planned, but I do have a couple of 300 or so mile trips planned and knowing how much gas you have is always a good thing, even on short cruises...LOL

At least I know that at half tank I have a half tank left....LOL

I didn't realize that they were that problematic. makes me want to get a new stock one & if it reads right then add the 3/8 line myself. Only difficult part would be to swedge the flat to get some more contact area to keep the line in place or some sleeve/nuts to anchor it. What are the stock ohms supposed to be? Was it 10 and 70