David, if you used a standard belt that is not designed to be twisted through the mule drive pulleys it will not last and will quickly derail. Spend the money and get a belt designed for that application and you will be money ahead.
EDIT: I see you are referring to the spindle belt, the belt that runs between the three spindles. Are the bearings nice and tight with no wobble? THat's a fairly long belt, a cheap replacement might be stretching. Did you get a Cub Cadet belt or a cheap "will fit" type?
EDIT: I see you are referring to the spindle belt, the belt that runs between the three spindles. Are the bearings nice and tight with no wobble? THat's a fairly long belt, a cheap replacement might be stretching. Did you get a Cub Cadet belt or a cheap "will fit" type?