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Hammer Drill: Hammer Drill Mode is Weak or Drills too Slow

If your hammer drill mode is weak or drills too slow, check out the following parts: the carbon brushes, switch, grease, and selector switch. Make the repair yourself by following our repair guide. Your hammer drill will be working at peak performance again in no time. Refer to your owner's manual for detailed instructions on your model.

Carbon Brushes
Carbon Brushes
Carbon brushes supplies power to the armature by riding on the commutator. Carbon brushes wear easy and when they do, it can limit their ability to provide enough current to the commutator for the armature to spin. The slower the armature spins, the slower everything else inside the hammer drill will operate.

To inspect your carbon brushes, remove the handle and open the case of the drill. This will vary as they are all different. With the case open, locate the brush holders and proceed to remove the holders by gently pulling up on them. On some models, release the hold-down clip and pull the brush out of the holder. Brushes 1/8 of an inch, or less, are considered worn and will need to be replaced. Install the new brushes in the holder and make sure they lock down. On other models, slide the brush into the holder and reapply...
Carbon brushes supplies power to the armature by riding on the commutator. Carbon brushes wear easy and when they do, it can limit their ability to provide enough current to the commutator for the armature to spin. The slower the armature spins, the slower everything else inside the hammer drill will operate.

To inspect your carbon brushes, remove the handle and open the case of the drill. This will vary as they are all different. With the case open, locate the brush holders and proceed to remove the holders by gently pulling up on them. On some models, release the hold-down clip and pull the brush out of the holder. Brushes 1/8 of an inch, or less, are considered worn and will need to be replaced. Install the new brushes in the holder and make sure they lock down. On other models, slide the brush into the holder and reapply the hold-down clip. Tuck all wires in their channels and reassemble the case back together. Finally, reattach the handle.
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Grease
Grease
A lack of grease will cause moving parts to move much slower than normal, heat up excessively, and lead to sever damage to moving parts. To inspect the inner-workers of the hammer drill, remove the handle and open up the case of the hammer drill. This will vary on different makes and models of hammer drills. With the case open, inspect all of the gears and moving parts for sufficient grease. Even some new hammer drills have been known not to be greased when leaving the factory. Pack the gears with grease. If the grease looks really dirty, you can clean it out and repack with new grease. Always use grease recommended by the manufacturer. Once you have lubricated everything, reassemble the case back together and reattach the handle.
A lack of grease will cause moving parts to move much slower than normal, heat up excessively, and lead to sever damage to moving parts. To inspect the inner-workers of the hammer drill, remove the handle and open up the case of the hammer drill. This will vary on different makes and models of hammer drills. With the case open, inspect all of the gears and moving parts for sufficient grease. Even some new hammer drills have been known not to be greased when leaving the factory. Pack the gears with grease. If the grease looks really dirty, you can clean it out and repack with new grease. Always use grease recommended by the manufacturer. Once you have lubricated everything, reassemble the case back together and reattach the handle.
Knobs
Knobs
The selector switch allows you to switch between the hammer drill mode and the drill mode. If the selector (knob or lever) is broken, you will not be able to switch between these different functions. If the selector (knob or lever) is jammed, it can impact the function of the mode it is jammed in, causing a power-flow disruption between the motor and the chuck. This will be visible by a weak hammer function or slow-moving drill. This will vary on models as different hammer drills have different cases. Pull the selector (knob or level) out, making note of how it is attached, and install the new selector (knob or level) in the same way the old one was connected. Make sure to locate and remove the broken piece from the internal workings of the hammer drill. Reassemble the case back together and reattach the handle.
The selector switch allows you to switch between the hammer drill mode and the drill mode. If the selector (knob or lever) is broken, you will not be able to switch between these different functions. If the selector (knob or lever) is jammed, it can impact the function of the mode it is jammed in, causing a power-flow disruption between the motor and the chuck. This will be visible by a weak hammer function or slow-moving drill. This will vary on models as different hammer drills have different cases. Pull the selector (knob or level) out, making note of how it is attached, and install the new selector (knob or level) in the same way the old one was connected. Make sure to locate and remove the broken piece from the internal workings of the hammer drill. Reassemble the case back together and reattach the handle.
Switches
Switches
If the switch is wearing out, it can produce more resistance in the flow of electricity. Signs of a failing switch will not always function when you press the trigger or everything else may be operating slower, if receiving less power. These signs will also be similar to worn out brushes.

To check the switch, remove the handle and open up the case of the hammer drill. All models are different, so this will vary. Begin by examining the carbon brushes to make sure they are not worn out as they can cause the same symptoms. See “carbon brushes” for removal and installation. Once you have determined the brushes are fine, proceed to remove the switch.

There may be a hold-down bracket, or screws, securing the switch down. Inspect the switch for any melting, or burning marks, indicating a malfunctioning switch. Inspect the condition of the wires and connectors at...
If the switch is wearing out, it can produce more resistance in the flow of electricity. Signs of a failing switch will not always function when you press the trigger or everything else may be operating slower, if receiving less power. These signs will also be similar to worn out brushes.

To check the switch, remove the handle and open up the case of the hammer drill. All models are different, so this will vary. Begin by examining the carbon brushes to make sure they are not worn out as they can cause the same symptoms. See “carbon brushes” for removal and installation. Once you have determined the brushes are fine, proceed to remove the switch.

There may be a hold-down bracket, or screws, securing the switch down. Inspect the switch for any melting, or burning marks, indicating a malfunctioning switch. Inspect the condition of the wires and connectors at the switch as well. Remove the connectors and transfer them on the new switch – careful not to mix up their position. Install the new switch in the drill case and reattach any hold-down screws, or brackets, securing the switch. Tuck wires into their appropriate channels. Reassemble the drill case back together and reattach the handle.
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