Worn brushes cause intermittent motor function, reduced braking and low power. Heavily inspect armature for indications of heat damage, cracks, or other damage that can be signs of more significant motor problems that may not be solved by replacing the carbon brushes. Carbon Brushes should slide all the way through the brush holder. Sandpaper can be used to achieve a perfect fit. Chamfered corners help ease assembly. Note: Carbon expands when heated, Allow room for Thermal Expansion.