Cordless Drill: Excessive Sparks From the Motor

To replace or clean the armature, remove the rear cover on the drill. Take out all of the screws on the cover to the case and remove the case as well as the two transmission screws on the side of the drill that the cover is attached on. Remove the hold down on the motor. Lift the motor and transmission assembly out and pull the armature and field away from the transmission. Pull the armature out of the field. If there is a heavy build up of dirt, you can clean it with thinner and then dry it thoroughly. Once cleaned, you can test it or reassemble it back into the field if you are confident it just needed a cleaning.
To check for a bad armature, you can perform the 180-degree test. With the armature removed from the unit, stand it up on a bench. With an ohmmeter, attach the two ends to both sides of the commutator to measure the resistance of the windings. As you move it around the commutator, the reading number is not important. You are looking for a consistent reading, indicating the windings are good. If it varies radically, reading a zero or open circuit, then the armature is not good.
Another test is reading. If the ohmmeter reads zero or open circuit, then that indicates a bad armature. The last test is a bar to ground test, which is done by placing one lead of the ohmmeter to the tip of the shaft of the armature and the other to the commutator.
If the armature is bad, install a new one. Install the armature into the field. The field will have a notch on it, indicating the front (which faces the transmission). Reattach it to the transmission. Now, install the one brush in the housing and then reinstall the motor/transmission assembly back in the housing. Install the other brush on the cover, then put the cover back on the housing. Finally, reinstall the two transmission screws and the end cap.

If the bearings become worn, or seized, they can cause the motor the spark excessively due to the seized bearing forcing the motor to work much harder. To replace a bearing, remove the end cap cover on the housing and the two transmission screws securing the transmission to the housing on the side of the drill where the cover is located. Pull the cover off. Pull the motor and transmission out of the housing and separate the two. Remove the armature from the field and then the bearings with a bearing puller and install the new bearing. Reinsert the armature back in the field, then reattach to the transmission and reinstall the transmission/motor assembly back in the housing. Ensure all of the brush holders and brushes are back in place. Reinstall the cover and the transmission screws, securing the transmission to the housing. Reinstall the end cap.

The brushes ride on the commutator and apply electricity to the armature. If the brushes become worn, wear unevenly or one (or more) of the springs are applying incorrect pressure, then this can cause the motor to spark excessively. Remove the end cap - on some models this all you have to do to access the brushes. Then, take out the two screws holding the transmission on the motor, on the side of the transmission where all of the housing screws are facing upwards on the case that secures the cover to the housing. Next, remove the screws securing the cover onto the case and remove the cover. One of the brushes is located in the cover. Remove the holder from the case and take out the screws securing the hold-down brackets on the motor and lift the motor up and then take out the other brush holder. With the brushes removed, inspect them for uneven wear, damage and weak springs. If you notice any of these signs, replace the brushes. When doing so, be sure to replace all of them at the same time. Replacing only one can still cause excessive sparking. Reinstall the first brush and holder back in the housing, ensuring you reattach the wire. Reinstall the motor and tighten down the holder, back in the housing, and reattach the wire. Reinstall the motor and tighten down the brackets as well as the second brush holder in the cover. Reattach the wire then put the cover back on the case and tighten all of the screws. Reinstall the transmission screws and then the end cap.

See armature on armature and field cleaning.

If the gears are jammed up inside the transmission, it can cause the motor to spark excessively since it cannot turn properly. To fix this, you can either try to un-jam the gears or replace the transmission. Insert a screwdriver into the drill chuck and snug the chuck up against the screwdriver and remove the screw, remembering this screw is reversed thread (turn it clockwise).
Next, insert a large allen wrench inside the chuck and tighten the chuck down on it. Hit the allen wrench with a hammer to loosen. You can also place a pipe over the allen wrench for leverage. Ensure you have the transmission set to the lowest setting before doing this. Next, remove all of the screws on the cover, securing it to the housing as well as the screws securing the transmission clutch assembly. Remove the cover and the transmission clutch assembly and then pull the gear selector switch out. Remove the motor from the transmission.
For most models, the planetary gears are visible. Inspect them for debris that may be causing the jam and clean it out. If there is damage on the gears, then replace the transmission. Marry the motor to the new transmission or the old one that you have cleaned out.
Reinstall the gear case and motor back into the housing aligning it up properly to lock in any grooves in the housing. Reinstall the gear selector switch. Put the cover back on the case, ensuring all of the wires are tucked inside the channels inside the housing. Reinstall the transmission clutch assembly to the case. Snap the brush springs back in place and reinstall the rear cover. Reinstall the drill chuck hand tight and put the screws back inside the chuck, remembering that it is reversed thread (turn counter clockwise to tighten).

If the motor has a heavy build up of dirt inside of it, it can cause excessive sparking. Remove the end cap on the drill. Then, take out the two screws holding the transmission on the motor, on the side of the transmission where all of the housing screws are facing upwards on the case that secures the cover to the housing. Now, remove the screws securing the cover onto the housing and remove the cover. Remove the screws securing the hold-down bracket on the motor and lift the motor out of the housing and separate it from the transmission. Some motors are sealed units, so place the motor in a bucket and soak it in thinner to clean. On some models, you can separate the armature from the field.
Clean with thinner and reinstall the armature back in the field. Dry thoroughly before reinstalling. Reattach the transmission to the motor and secure it back into the housing. Tighten it down with the brackets. Reinstall the case back in the housing and reattach the two screws, supporting the transmission to the housing. Reinstall the end cap.

Any physical damage to the holder, or a heavy build up of dirt inside, may interfere with the free motion of the brush in the holder, resulting in sparking. Since the commutator is not perfectly round, the brushes must move in and out of their holders in order to maintain effective contact. A visual examination and testing of the free action of the brush with the fingers are usually sufficient to reveal this condition. A thorough cleaning or complete replacement will improve operation.
Begin by removing the end cap on the drill. Next, remove the two screws holding the transmission to the motor, on the side of the transmission where all the housing screws are facing upwards on the case that secures the case to the housing. Now, take out the screws securing the cover onto the case and remove the cover. One of the brushes is located in the cover. Take the holder from the case and then remove the screws securing the hold-down brackets on the motor and lift the motor up and remove the other brush holder. Inspect both brush holders for damage, including wear on the brushes, and replace as needed. If they are in physically good shape, then clean thoroughly.
Reinstall the one brush holder back in the housing, making sure it is all of the way. If the brush holders are not in all of the way, or are positioned a little out of alignment, it can cause excessive sparking as well. Reattach the wire. Reinstall the motor and tighten down the brackets as well as the second brush holder in the cover then reattach the wire. Put the cover back on the case and tighten all of the screws. Reinstall the transmission screws and put on the end cap.