Yeah, Its springtime again. Some of us are probably washing off the dust to make our cars ready for the local shows and races. I just got back from a 900 mile round trip from Sacramento to LA for the Spring Fling. I used 6 tanks of gas and even with the tank full enough to be within 6 inches of the Chargers filler cap, the guage never read over 3/4. With 9 gallons in the tank, it reads 1/4. I still have 4 gallons when it reads empty. Its always off by at least 1/4 tank, but at least it is consistant on each tankful.
My electrical testing skills are pretty limited. I remember that in previous posts about testing sending units, some have written that the rheostat (?) should show a certain reading at FULL and another at EMPTY. That makes sense, but what if I have a unit that spec's out different than the prescribed numbers? How is it corrected? I tried bending the float lever and it still reads the same. I'm considering taking a good used 5/16" sender and converting it to 3/8" since none of the aftermarket senders seem to be much better than mine. Any comments?

I suspect a sinking float but no matter what you do the sending unit will have to be removed. pop the float off and shake it to see if it has any fuel in it. If it does you have the choice of a brass stock float or a plastic Ford#COAZ-9202-B
If that's OK check the resistor with an ohmeter. 10 full,70 empty. Adjusting this is beyond my ability but a thread ran a while ago about grounding the resistor to the body of the sending unit.
Hope this helps,
Ron

I swapped out to the new 3/8 unit...and I am probably going to put the 5/16 unit back into my tank...Reason being for the same problem you are having...Plus I figure since the rest of the hard line from the tank to the engine bay is factory....a 3/8" in the tank is useless...like shoving a tennis ball through a firehose....it could eventually get through but with great resistance.

Yea, I have the same issue on my BEE. Full it reads ½ and half it reads empty. I just make sure I never go more than 200 miles with out filling up. I’m not even going to mess with it. Wait, It’s been that way for almost 20 years.

most of the cars i see have this problem , i have restored three b bodys and all do the same thing 5/16 , 3/8 does not matter .
i have replace the wire from the back of the guage cluster to the sending unit , made sure the sending unit is grounded and changed floats to brass from plastic .
this all had no effect on the guage , reading !
Here is the weird part , if you hold the dang thing in your hand with all the connections made i can move the float by hand and make it go full and to half when out of the tank . Unbeliveable right I know!
my take on this is some thing has been lost from the factory units to the aftermarket , either wrong calibration OR the float hits the top of the tank when inside the tank so it will never read full .

someone said you have to bend the arm on the sender, i don't know if this works or not . might be worth a try bending it down so it will rise higher in the tank .

OK, here's the problem with most of these. Make sure the sending unit in the gas tank has a ground. The factory used a 4 to 6" clip which spanned the length of rubber hose from the gas line to the sending unit. This should solve most of these problems. There is one other thing you can do. In the back of your fuel gauge in the dash, there is a small hole. Inside this hole you'll find a small gear looking adjustment. Put a screw driver in the opening and move the gear a little and your gas gauge will go up or down. One other thing to check, You might have a bad voltage limiter in the dash. Put a voltage meter on the output of the limiter. It should pulse from 0 to 5 volts.

I had the same problem. I ended up cutting a good sending unit off a factory 5/16 unit and attaching it to a repro 3/8 pickup tube. I attached the sending unit to the pickup tube with 2 small hose clamps after trimming the side of the clamps a bit to slide thru the 2 small slots in the sending unit, and connected the factory style wire to the strap wire on the repro. Works now.

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someone said you have to bend the arm on the sender, i don't know if this works or not . might be worth a try bending it down so it will rise higher in the tank .

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For me it wasn't a matter of bending the arm, it was bending the upper stop tab so the arm would swing a teeny-tiny bit farther.

Worked like a charm in my case.

Like investing in the stock market, your results may differ.

I went overkill for my sending unit...I have the original 5/16" unit which I am popped out for a 3/8". Both setups were installed the same way. I have a 14gauge wire soldered to the sending tube below the rubber hose. From there it goes to its own dedicated ground on the frame. I ran a wire all the way from the sending unit, into the harness, and to the old fuel gauge.

With my old gauge it worked but I had restored a second cluster professionally and it still came up just below full tank. This was about the time I swapped units.

I have a brand new brass float from a Ford thats a perfect match for it. Should get around to doing that task soon. Would like to have fuel when I am driving