Whilst visiting parents, I got called upon to investigate vacuum cleaner. Apparently, whilst being used, the motor started slowing down and giving off a burning smell. I was expecting a motor brush to have worn out, but on investigating, the brushes were fine. The commutator was a bit dirty, which I cleaned up with some fine sand paper, but there was nothing else obviously wrong with the motor. When I had the brushes out, the armature spun very freely in its bearings. Having reassembled it, I ran it for a few minutes without the brush bar belt, and the drive shaft had got hot enough to burn me, although the motor didn't slow down, so I'm not sure if I changed things by cleaning the commutator. Connected back the brush bar and used it for a few minutes -- smell of hot electrics, although it seemed to be working. I had also cleaned the internal filters, but they weren't heavily clogged, and the bag was only a 1/3rd full.
Any suggestions what might be wrong with it? If it's a gonner, would be good to get a new one while the sales are on.