Gas gauge issues

[keith88]

I have a issue with my gas gauge in my 69 when i fill it it reads only half full. The guy who had it before me put in a new tank and sending unit and said it worked fine (before he changed it) but he never put more than a few gallons of gas in it before i bought it so he would not have seen this issue.  I did put a  ground strap on it that was missing but made no difference, and i tested the gauge its self by grounding out the wire to the sending unit that did go to full.
I have been researching this and i have found some info on liner and none liner sending units and i think this may be the problem, has anyone had this problem and what did you do to fix it . Any other enlightenment on this is welcome as well Thanks.

[Ghoste]

Fairly common with reproduction sending units.

[AZMoparboy]

Hi, hope this works for you. This is what I did. You have to take the sending out of the tank, figure out that direction.you have to bend the float, give it a little tweak, up or down, whichever way it needs to be done to make the gage read better, again, this worked for me.

[fy469rtse]

There was a post recently Keith about a new correct reading batch that was available shortly
Or I haven't done it, but a friend off mine re calibrated his gauge to match ohms reading on sender unit , worked like a charm , beyond me but going to ask him to do mine ,

[Ghoste]

It is Dixie Auto Parts that are trying to get some correct ones reproduced by the original vendor.

[keith88]

Bending the float it self is something i thought of,but how accurate would that be on the lower end in my case ..still not sure if that would fix it. The calibration thing is a neat idea but i have no clue what to do there.
Does anyone know if it possible to buy a gauge that would match the liner sending unit? And what should one look for when doing that?

[XH29N0G]

As I understand it, the gas sending unit sets up a resistance on a 5v dc circuit.  This changes the current though the gauge.  My understanding of the issue with the replacement sending units has to do in part with them having the incorrect high and low resistance readings.  There may also be an issue of how the intermediate resistance (like at 1/2 full or 1/4 full) match up with the resistance.  Others on here will know more than me on this, but may be able to advise on how to test the sending unit resistance.  It seems to me that you want to have the float bent so it moves properly in the tank and also have the correct resistance through the sending unit. 

I had another thing that I am not sure if it was the reason, but the gauge read differently after I cleaned up the contacts with the Aluminum nut to the copper on gauge cluster.  Mine was reading 3/4 and then shifted up to full.  I am still not sure if I have another issue that caused this, but it made me wonder if resistance on connections in the gauge to sending unit to cluster voltage regulator might also have an effect on these older cars.

[Dino]

There is no way to bend the float arm to read correct all over the scale, but it can show you when it's either empty, full, or half pretty good, just not all 3.

Get a hold of an old sending unit and if you can't find a decent used one then find one that's beat up and remove the resistor, discard the rest of it.  Remove the resistor on the new sending unit, throw it away, and weld the old unit's resistor to the new sending unit.  Fill the tank with around 10 gallons and drop the sending unit in place.  Jack stands are almost a must here to get decent access.  The gauge should be roughly in the middle.  If it's not then remove the unit and bend the float arm until it does.  If the needle is way off middle then I suggest you remove the gauge and calibrate it first.  I only had to give mine a tiny bend and it reads spot on over the entire range.

If you can't find an old sending unit then I suppose you could make the new unit non linear with some Radio Shack supplies but it gets a bit more involved now.