Classic/Antique Car Repair: 6 mustang fuel gauge, gauge works, fuel gauge

Question
The fuel gauge on my 66 mustang was stuck on empty.  After trouble shooting the situation, checking to make sure the wiring worked and checked the tank ground, we determined that there was an issue with the sending unit. I recently replaced the unit and found that the float was no longer attached to the old unit.  After installing a new sending unit,the fuel gauge works, but will only read up to about 3/4 of a tank when the tank is full.  I made sure the tank was as full as I could get it, actually overflowed a little, but the gauge raises to just short of 3/4 of a tank and stops.  Any advice on what I need to do to get the gauge to read full?

Answer
Sounds lke the new sending unit needs to be calibrated for your car. Much like adjusting the float on a carb. This actually does not have to be in tank to do this, but you must be able to see where float rise stops. Then adjust (usually bend) float until 'full' is read.