Your drill's motor uses two carbon brushes to conduct electricity to the armature. The brushes conduct electricity to the armature through its commutator. The carbon brush will wear down (over time) from rubbing against the rotating commutator (and will need to be replaced). Worn brushes can cause excessive sparks around the commutator. The sparks can also be caused by a damaged armature, so you'll want to carefully inspect both if sparks are present.
Let's get started.
REMOVING THE CARBON BRUSHES 1. Remove the carbon brushes.
a. Use a large screwdriver to remove the brush cap.
b. Remove the carbon brush from the brush holder.
c. Repeat this step to remove the second carbon brush (located on the opposite side of the motor).
INSTALLING THE NEW CARBON BRUSHES
2. Install the carbon brushes.
a. Install the new carbon brush into the brush holder.
b. Align the metal "wings" on the end of the brush spring with the slots in the brush holder and compress the spring into the holder.
c. Secure the new carbon brush with the brush cap.
d. Repeat this step to install the second carbon brush (on the opposite side of the motor).