On the advice of Consumer Reports and others, I purchased a Hoover U5140-900
vacuum cleaner a couple of years ago. As of today, it has broken two belts. My
daughter had it in her apartment at college, so it has not had heavy use.

After I took it apart, I checked the motor pulley to see if it had any dirt
accumulation. Since it did, I turned on the power to the vacuum and held a paper
towel against the pulley to clean it. Much to my surprise, it burned my finger.
Thinking that the friction between the pulley and my finger would easily explain
the burning sensation, I turned off the power and then felt the pulley (which
really looks more like a spindle to me). It was very hot. There is no way that
the friction between the pulley and the paper towel caused it to heat that much.
Therefore, I have to conclude that the motor is heating the pulley.

The pulley has to be getting hot enough to weaken or melt the belt. I haven't
taken the motor housing apart to see if there is an obstruction, but before I
dig too deeply, I wanted to ask whether anyone here had heard of such a problem.
My guess is that the bearing in the motor where the pulley protrudes is bad. If
that's true, I doubt the unit is worth repairing, if you can even get a motor.
It's not an expensive unit anyway, but it was highly rated.

Here is the manual: http://www.hoover.com/pdfs/manuals/U5140900.pdf There is not
much there in terms of servicing information.