Problem with replacement petrol gauge

[sogama]

I have a Euro 1991 S4. I bought the car 2+ years ago, and the petrol gauge on the dash has never worked properly - it never went below 3/4 even when the tank was virtually empty (I posted about this at the time). After cleaning the clock set electronics, and generally fiddling with the pod to no avail, I have just bought a second hand clock set from a 1991 S4. It looked like it was working fine (the tank was 1/4 full when I replaced it, and gradually went to zero as I used up the petrol), but when I filled up, the dial only went up to 3/4! It also seems to "wander" slightly up and down depending on the "miles left in the tank" reading on the digital dash (which it does depending on the then current petrol consumption). In case it matters, all the digital dash readings work fine, as do all the other dials.

My question is, is the gauge not going to full because it needs to be calibrated in some way, or have I purchased a dud clock set?

[MarkRobinson]

I'd remove your sender out of the top of the tank (accessible through the trunk: open trunk, remove carpet & pad, remove round plastic cap to expose tank below, unscrew head of tank (where breather line & sending wires reside), pull out sending unit & observe if you have full, unobstructed travel: scotch-brite away (scrub) any residue or gunk resulting from gas sitting too long in your tank).

For the digital gauges, I wouldn't imagine there were any adjustments, though, when the sender is out, you can check the wiring connection on top of the tank to ensure it's not corroded or dirtied up.

[sogama]

Thank you for the suggestion. Just to clarify the situation, the problem is with the analogue petrol gauge (the dial), not the digital one.