That can be a concern, as the brushes get shorter.As the brush shortens,
the
spring tension that keeps it against the commutator is reduced. This, in
conjunction with the shorter brush more readily transferring heat to the
brush holder, makes sticking a possibility. Add to this, increased armature
run out, caused by fair wear & tear, of both the commutator bars, and the
armature bearings, and the recipe is complete. This input was gleaned for
my
Dad's many years of maintaining DC operated overhead cranes, and small
Diesel / Electric switch engines.
RJ Kanary