Replace Motor Carbon Brushes
Helpful information about the fitting of motor carbon brushes in general terms, applies to no particular brand of carbons!
First! If you are going to examine the motor brushes! Utmost importance! Disconnect the appliance from the mains electricity supply! Do this by removing the plug from the supply socket or by switching off at the main consumer unit. This can usually be accomplished by switching a single breaker, which, if it is an up to date RCD (residual current device) hopefully it will have been labeled Kitchen Sockets, Utility Room Sockets, House Sockets, Garage Sockets, you get the idea, where ever your appliance is situated. It may also be a wise move to ask anyone who is working at a computer that is mains powered to back up their work before switching off.
Carbon brushes are used in motors known as Universal motors, this is because they will run equally well on AC or DC current. Brushes come in all shapes and sizes, they are usually, but not always, sold in pairs, and come with enormous variations in the material composition of the brushes themselves. This composition is usually made up of copper and carbon, and depending on the manufacturers requirements may have different proportions of copper to carbon depending on the hardness or softness of brush that the manufacturer has specified. More copper, the harder the brush and therefore more hard wearing, conversely more carbon and less copper the softer the brush so wears more quickly. The manufacturer of the motor determines the specification of the brush, depending on the hardness and quality of the motor commutator, the speed and the power rating of the motor, always trying to strike a balance between long life and not doing too much damage to the commutator during the life cycle of the motor, and allowing the brushes to brush against the rotating armature without wearing out too quickly.
Brushes should be replaced regularly to achieve maximum life from the motor, similar to oil in a car engine, it is too late when the brushes have worn down to very end and the copper retaining strap and the spring have begun rubbing on the commutator and worn a groove in the center of it, so checking the motor carbon brushes should be a priority of every service check.
When it comes to actually replacing the motor carbons it is always best to use a good quality brush set, if the brush is inside a plastic housing, check that the brush is free to slide in and out of the unit and has a good amount of movement. Check also that the connection on to the connector tag is a good tight fit, it is no good being a loose fit as it will only burn or at the very least get hot at this point, poor connections mean heat in everything electrical and heat means at worst, burning, and at best, loss of power in the motor.
Hope this helps, and good luck with your repair project!