Fuel Guage - guestimate

Can anyone explain the fuel sender set up in a series 3 to me? My guage reads 1/4 tank when full, and then stays there until it plummets to empty and a couple of miles later runs out of fuel. The speedo cable is snapped so I have no idea how many miles i've done to judge when to fill up (although i'm replacing that this weekend), so often end up topping up every few days or running out.

Before I open up the tank to check the sender set up is this a common problem? Is it a float type fuel sender that may just need adjusting to read higher when actually full? Or is this just something thats normal and I have to get used to?

cheers

The sender in the tank is fubar, easy replacement and cheap.

As storm says its most likely the sender,contacts often corroded.

disconnect the cable on top of the sender and hold directly to earth (e.g. metal plate on sender) the fuel gauge should then rise to read full - if it does then faulty sender, so replace

I've had the exact same problem. Even bought a new instrument cluster to test out the guage. Turned out to be faulty +ve wiring to the guage. The sender unit is just a variable resistor but in my mind I always pictured this on the +ve side of the circuit. In fact, is resist on the return side / -ve leg (hence the one wire going back to the dash from the sender unit).

I worked this out by jumping a cable straight from the +ve terminal on the battery straight to the guage. Straight away I got an accurate reading.