WARNING: Failure to change your vacuum cleaners belt at least once a year will takes years off the life of your carpets and flooring. A litle rubber band is the cheapest and the most important part on your vacuum cleaner. It must be tight enough to make the brush roll spin fast enough when its forced into the carpets fibers to agitate and loosed the heavy soils so the vacuum can suck them out of the carpets.

WHY do vacuum belts NEED Changed if they're not broken?
It's hard to get a new vacuum belt on because it is much shorter than the old belt. Every day your belt looses elacsticity (think of a 2 inch rubber band that you stretch to 4 inches and leave it that way for a few months) Even if your vacuum has never been turned on the belt is stretching and loosing elasticity as you read this. Each day it doesn't work quite as well as the day before. It may still pick up hair and  dust but can't agitate the heavy sandy, gritty soils to the surface of the carpet fibers to be vacuumed out. After 6 months the brush-roll really starts to slow down. It may even stop spinning completely when it contacts the carpet. 

Slipping belts and/or brush-roll agitator may cause the following: 

1. 1.     pre-mature wear of the agitator
2. 2.      poor sweeping results. 
3. 3.     Shortened belt life and performance