You don't need to remove the motor. Just remove the two screws from the top motor cover - ensure the mower is NOT plugged into the mains socket! When the cover is removed the top of the motor is exposed and you will see two springs - one either side of the central rotor - each holding the carbon brushed against the rotor. Using a small screwdriver, carefully remove the springs and the carbon brushed slide out. Unplug the spade terminals and replacement is just the reverse of this procedure.
Glenn Pollard, February 2015
