gas gauge

hi car pros..im having a little problem with my gas gauge..i just replaced my fuel pump for the second in a month but anyway when i replaced my first full pump the gas gauge read a quarter of a tank when it was full..and sence i put this last pump in it stays on E with the gas light on,and the car is almost full of gas..the last time i noticed when i dropped the tank the floater arm feel off some how it was at the bottom of the tank..do you think this could have happen again? if so y does it keep falling off now? the arm just slides in a little hole..what do you think my problem is? thanks!...