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How to Know When Carbon Brushes Are Worn and How to Replace Them in Grinders and Drills
Quick answer: Carbon brushes press on the motor’s commutator and wear down with use. Replace them when they are about 5–6 mm long or shorter, or when you see heavy sparking, loss of power or the tool cutting out. Unplug the tool, open the brush caps or housing, fit a matching pair (always both), run the tool unloaded for a few minutes to bed them in, and check the switch if problems continue. Bosch brush sets cost from KSh 360 on H-TECH’s listings.
Key facts
- Replace at about 5–6 mm
- Always replace in pairs
- Unplug before opening
- Run-in unloaded
On this page
Signs Your Carbon Brushes Are Worn
- Heavy or ring-shaped sparking at the vents.
- The tool loses power or speed under load.
- It cuts out or starts only when moved.
- Burning smell (also a sign of overheating windings: stop and check).
- Many tools have auto-stop brushes that cut the motor when worn.
How to Replace Carbon Brushes
- Unplug the tool (or remove the battery).
- Find the brush holders: screw caps on the sides of the motor housing, or under the rear cover.
- Remove the old brushes; note which way they sit and how the spring is fitted.
- Measure them: replace at about 5–6 mm, or when uneven or chipped.
- Blow out carbon dust; check that the commutator is smooth (deep grooves need a workshop).
- Fit the new matching pair, springs seated correctly, and refit caps or cover.
- Run the tool with no load for 2–5 minutes so the brushes bed in.
Bosch Brushes, Switches and Motors
Carbon Brushes Repalce for Bosch GSB180-LI GSR180-LI GSR140-LI GSB140-LI GSR18V-21 1607000CZ1 PowerKSh 360
Carbon-Brush Set for Bosch GDX GDR Impact Drills - Genuine Part - OEM No. 160701418RKSh 600
BOSCH CARBON BRUSH SET (1604321174)KSh 600
Carbon Brushes for Bosch GBH 18v-20 Cordless Drill Hammer 1619p14345KSh 600
Bosch 2610920682 Carbon Brush Set for RS10. RS15, RS20, RS35 Reciprocating SawsKSh 360
SWITCH FOR BOSCH GSB180-LI GSR18V-190 GSR180-LI 2607202330 CHARGE DRILLKSh 2,580
SWITCH FOR BOSCH GDR120-LI 2607202312KSh 2,390
2610925949 Switch: Genuine BOSCH Spare-PartKSh 1,290
2609199428 Motor - BoschKSh 1,390
DC 18V Motor for BOSCH GSR18V-190 GSB18V-21 GSR18V-21 GSR180-LI GSB180-LI 160702266NKSh 2,590
Motor for BOSCH GDR120-LI 1600A00PE3KSh 1,390
Teeth DC Motor 1607022649 HC683LGKSh 4,970Current listed prices incl. VAT (updated 13 October 2026).
Match the part number or tool model on the product page to your tool. Cordless tools also wear brushes (on brushed motors) and switches; replacement switches fix tools that start only at certain trigger positions.
When It Is Not the Brushes
| Symptom after new brushes | Likely cause |
|---|---|
| Still no power | Switch, cord or connections |
| Strong sparking continues | Damaged commutator or armature |
| Smoke or burning smell | Burnt armature or field windings |
| Grinding noise | Worn bearings or gears |
For motors, compare repair and replacement in rewinding vs replacement. Running a workshop? See how to start a stainless fabrication business.
Make Brushes Last Longer
- Do not force the tool; let the disc or bit do the work.
- Keep vents clear of dust.
- Use the right disc or bit for the material.
- Rest the tool when it gets hot.
Watch: Fabrication and components
Frequently asked questions
How do I know if my carbon brushes are bad?
Heavy sparking, loss of power, the tool cutting out or brushes shorter than about 5–6 mm.
Should carbon brushes be replaced in pairs?
Yes, always replace both brushes together.
How long do carbon brushes last?
It depends on use; heavy daily grinding wears them much faster than occasional drilling.
Why does my angle grinder spark a lot?
Worn brushes or a damaged commutator.
Do cordless drills have carbon brushes?
Brushed cordless tools do; brushless tools do not.