Brushes are little rectangular, graphite fellows on springs that deliver electrical power to the rotating part of the motor. Like a pencil, they wear out over time and when they begin to fail badly the motor runs rough and sometimes a bit smelly.
Heres a vid of someone changing WM motor brushes on a bench...
http://www.youtube.com/watch?v=0GmtRBiXLFc
From what you say, however, I doubt that you have a problem with the brushes - not if the wash cycle works OK - with bad brushes the spin cycle would be slow, rough, noisy, smelly and lumpy.
If the motor works during the Washing Cycle but not on the Spin cycle then you may well have a control or motor control issue - call an engineer.
Good luck...
Peccavi, April 2009
