"so I have a carrying capacity with out cargo disk of 8040 and with cargo disk 9540."

You are wrong again. 9540 - 8040 = 1500 that your disk carries right?

There is no disk that carries that little amount, Smallest is 2000 bulk (= 200 Mith ore), largest is 13500 bulk (= 1350 Mith ore).

If you have some disk that only carries 1500 you need a new disk.

http://www.istaria-lexica.de/Cargo_Disk