Household drive belts transfer power from a motor to a pump, fan, or drum. They typically wrap around pulleys but may wrap around a drum at one end. A correctly tensioned belt should deflect 1/2 to 3/4 inch midway between pulleys under thumb pressure.
Caution: Unplug or turn off an appliance before servicing its drive belt.
A cracked belt or one that can’t be properly tensioned must be replaced. Loosen the belt-tensioning device. If the motor bolts go through slotted holes, loosen them and push the motor toward the pulley it drives.
Push on a spring-loaded idler pulley to compress the spring, then slide off the old belt. If a pulley is a take-apart type, remove the bolt holding its halves together; the belt will come off.
Take the old belt to the hardware store to get an exact duplicate: same width, close in diameter (perhaps a bit smaller to allow for stretch), and its cross section the same.
If you have replaced a belt or if it is loose, adjust the tension so that the belt deflects less than 3/4 inch. Tensioning is basically the reverse of the removal procedure. However, you also may have to pry on the movable part to hold adequate belt tension while you tighten the bolts.
Reassemble a take-apart type with the number of shim washers originally between the pulley halves. Belt too loose? Take apart the pulley again, remove the shims, then reassemble(storing the shims against the outside pulley half). The pulley halves will move closer together, forcing the belt to ride higher in its grooves and increasing tension. To reduce tension, insert shims between pulley halves.