Worn Carbon Brushes: 5 Signs and How to Replace Them

Many corded angle grinders, circular saws, drills and rotary hammers use a brushed motor. Two small carbon blocks — the brushes — carry current to the spinning part of the motor and slowly wear down with use. Replacing them is one of the cheapest repairs you can do, and it often brings a "dead" tool back to full power.

Brushless tools don't have carbon brushes. If your tool is marketed as brushless, the problem is elsewhere.

5 signs your brushes are worn

1. Heavy sparking visible through the motor vents (a little sparking is normal; a ring of sparks is not).
2. Loss of power or the tool slowing down under light load.
3. The tool cuts out or only runs when you wiggle the cord or press on the housing.
4. A burning smell during use.
5. The tool stops completely. Some brushes have an automatic cut-off that stops the motor on purpose when they reach their wear limit, to protect the commutator.

How to replace them

1. Unplug the tool.
2. Find the brush holders. Many grinders and rotary hammers have two screw-in brush caps on the sides of the motor housing. Other tools require removing the rear cover or opening the housing.
3. Remove the old brushes. Note how they sit and which way the curved face points.
4. Check the length. Compare the old brushes with the new ones. If they're worn close to the minimum length in the manual — or unevenly worn — replace them.
5. Fit the new brushes as a pair. Always replace both brushes at the same time so they wear evenly.
6. Refit the caps or cover, making sure the springs and leads aren't pinched.
7. Break them in. Run the tool with no load for a few minutes so the new brushes seat against the commutator before heavy work.

Getting the right brushes

Brushes are made for specific tools, and the same model can use different brushes between "Type" revisions. Search by your tool's model number (including the type, if there is one) or by the part number on the old brushes, and check the Compatible models list on the product page.

If the tool still sparks heavily with new brushes, the commutator may be worn or damaged — that's a job for a repair shop.