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How to service your hammer drill

Introduction

Regular service keeps your hammer drill working hard despite the dust, vibration and heavy loads it sees on construction sites. Replacing worn carbon brushes, repairing a damaged power cable and packing fresh grease into the gearbox prevents overheating, loss of power and premature gear wear. Follow these instructions whenever the drill shows sparking, intermittent power or a noisy hammer action.

What you need

  1. Edit

    • Pull the power plug out of the mains before starting any work.

    • Always follow the manufacturer’s instructions because opening the drill can affect your warranty.

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    • Unscrew the brush cover on one side of the motor housing.

    • Lift the carbon brush straight out of its holder.

    • Unscrew and remove the second brush on the opposite side.

    • Draw an arrow on each brush showing its original direction for reassembly.

    • Replace the brushes once the graphite is worn to about half its original length.

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    • Remove the screws securing the rear handle around the cable entry.

    • Pull the housing halves apart and release the strain relief clamp.

    • Check the cable insulation for cracks, nicks or exposed conductors.

    • Heavy-duty use often damages the cable right at the grommet area.

  4. Edit

    • Photograph the switch and all wire connections before disconnecting them.

    • Mark the live conductor location labelled “L” on the switch.

    • Note the red-painted wires that run from the switch to the motor windings.

    • Pull the live, neutral and earth wires off the switch terminals.

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    • Blow compressed air through the stator slots to remove packed dust.

    • Wipe the rotor shaft and lamination surfaces clean.

    • A dry scraping noise suggests the rotor bearings need fresh grease.

  6. Edit

    • Unscrew the gearbox filler plug using a pin spanner or needle-nose pliers.

    • The opening exposes the hammer mechanism and gears.

  7. Edit

    • Scoop the dried grease out of the gearbox cavity with a suitable tool.

    • Wipe the gear teeth and housing clean of residue.

  8. Edit

    • Spread fresh high-pressure grease generously onto the gears and rollers.

    • Professionals often use a cartridge gun to push grease deep into the mechanism.

  9. Edit

    • Coat the upper gear section with the same thick layer of grease.

    • Screw the filler cap back on and tighten it firmly.

  10. Edit

    • Cut off the damaged section of the power cable.

    • Strip the outer jacket and the individual conductors to the required length.

    • Tin or crimp ferrules onto each conductor for a solid electrical connection.

  11. Edit

    • Feed the prepared cable through the strain relief hole in the handle.

    • Tie a knot or clamp the strain relief so the cable cannot pull out.

  12. Edit

    • Attach each conductor to the same switch terminals shown in your photo.

    • Gently tug each wire to check that the terminal screws hold firmly.

  13. Edit

    • Align the housing halves and tighten all handle screws.

    • Slide each marked carbon brush back into its holder with the arrow facing the commutator.

    • Screw both brush caps fully home to secure the brushes.

Conclusion

With new grease, a sound cable and correctly seated brushes, your hammer drill is ready for many more hours of heavy work. Keep dust out, store it dry and repeat this service whenever sparks increase or the hammering gets noisy.

Author

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Ula Gantar

Member since: 01/08/25

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