Dodge Repair: 1995 PLYMOUTH VOYAGER, plymouth voyager, gas gauge

Question
GAS GAUGE IS NOT LINEAR.. AFTER ABOUT 200 MILES IT DROPS FROM 3/4 FULL TO 1/4 ABRUPTLY.. CAN ANYTHING BE DONE ABOUT THIS? VEHILCE HAS ONLY 46,000 MILES.

ALSO THE VEHICLE GOT HIT IN THE REAR ( DRIVERS SIDE)AND THIS CYLINDERICAL BLACK TUBE ,(FEELS LIKE A SPRING IS IN IT,)  FELL OFF.
THIS BLACK THING IS LOCATED NEAR THE PARKING BRAKE
ADJUSTER, ON THE UNDERSIDE OF THE VEHICLE. I CANT'T FIND ANY IFORMATION ON WHAT THIS DOES OR WHAT IT IS.

ANY SUGGESTIONS ON KEEPING THE THE 3.0 LITER
ENGINE IN GOOD SHAPE. I HAVE A LIFTER NOISE WHEN IT STARTS, BUT THEN GOES AWAY AFTER 15 MINUTES OF DRIVING.

THANKS IN ADVANCE FOR YOUR HELP  

Answer
Hello joe
since the car got hit in the rear . i would check the ground wires on the tank for the droping in the gage .

As the spring i will get back to u i have to see what you are talking about my self when i go in to the shop i will search my books pete