The grinder that cut every gate frame for three years starts to spark around the vents, smells hot after ten minutes and then stops dead halfway through a job. The fundi shakes it, it runs for a few seconds and dies again. Many people in that position buy a new grinder the same afternoon. Very often the old one only needed a pair of carbon brushes that cost a small fraction of a new tool, and a blast of air through the motor to clear out three years of dust.
Corded angle grinders, drills, rotary hammers, circular saws and planers share the same basic motor and the same handful of wear parts. They fail in predictable ways, and almost all of those failures announce themselves weeks in advance through sound, smell, sparking or a cable that has started to crack. A workshop that learns to read those signs, and spends ten minutes a week on simple care, gets years more from every tool.
This guide explains what wears inside a power tool, how to replace carbon brushes, how to keep dust and damp out through the short rains, and which faults belong with a trained repairer. Your tool's manual has the final word for that model.
What Wears Inside a Corded Power Tool
Most mains powered hand tools use what engineers call a universal motor, a brushed motor that runs on AC or DC. The spinning part, the armature, carries a ring of copper segments called the commutator. Two small blocks of carbon, the carbon brushes, are pressed against the commutator by springs and carry current into the armature as it spins. Brushes are made to wear away gradually so the copper does not. That is their job.
The other wear parts sit around it. Two or more bearings hold the armature shaft. A small fan on the shaft pulls cooling air in through the rear vents and blows it out at the front. A gearbox, in a grinder or a hammer drill, turns the motor's speed into torque at the spindle and runs in grease. Then come the parts you touch: the trigger switch, the power cable and its strain relief, and the plug.
Brushless cordless tools have no carbon brushes; the motor is switched electronically. Everything else in this guide applies to them too.
Carbon Brushes: Signs of Wear and How to Check Them
Worn brushes give clear warnings. The tool loses power under load, cuts out and restarts when you move or tap it, or will not start at all. Sparking at the commutator becomes heavier: a few small blue sparks visible through the vents are normal on a brushed motor, but a ring of sparks running right round the commutator, or orange sparks with a burning smell, means something is wrong. The cause may be worn brushes, a sticking brush, or a damaged commutator.
Many tools have screw caps on the outside of the motor housing, one on each side, that let you pull the brushes out for inspection without opening the tool. Others need the rear housing removed. Unplug the tool first, every time. Take out one brush at a time so you put each back in the same holder and the same way round, because a used brush has worn to the curve of the commutator.
Look at three things. First, length: compare it with a new brush or with the wear limit in the manual. Second, the face: it should be smooth and evenly polished. Chipped, cracked, burnt or glazed faces point to a problem. Third, the spring and lead: the spring should still press firmly, and the braided copper lead should be intact and not burnt.
Some makers fit what they call auto-stop or cut-off brushes. These contain an insulating pin that pops out when the brush reaches its wear limit and breaks the circuit, so the tool simply stops. If a fairly new tool dies suddenly with no smell or smoke, worn auto-stop brushes are a likely cause, and a new pair brings it straight back.
Replacing Carbon Brushes the Right Way
The sequence below works for most grinders, drills and hammers with external brush caps.
Always replace brushes as a pair, even if one looks better than the other, so both press evenly on the commutator. Use the brush made for that model, or an exact match in size, spring and lead. A brush that is slightly too narrow rattles in its holder and sparks; one that is too tight sticks and stops touching the commutator as it wears. Take the old brush and the tool's model plate details when you buy.
After fitting, run the tool with no load for a few minutes. New brushes have a flat face that has to wear to the curve of the commutator, and until they do, sparking can be a little heavier than usual. If heavy sparking continues after this run-in, or you see deep grooves, burnt or lifted segments on the commutator, stop. The armature needs attention from a repairer, and fitting more brushes will not cure it.
Dust Is the Silent Motor Killer
The cooling fan pulls air through the motor all the time the tool runs, and it pulls whatever is in that air with it. In a Kenyan workshop that means steel grit from grinding, cement and stone dust from chasing and drilling, and fine wood dust from planing. Steel dust is conductive and abrasive. Masonry dust is abrasive and packs into the windings. Both block the airflow, so the motor runs hotter, and heat is what breaks down winding insulation over time.
The routine is simple. At the end of a dusty day, with the tool unplugged, blow compressed air through the vents from the front and the rear, wearing eye protection and pointing the dust away from your face. Our guide to air compressors explains the air supply; even a small compressor does this job. If you have no compressor, a dry, soft brush on the vents is far better than nothing. Never wash a motor with water or spray solvent into it.
Supply matters too: a tool on a long, thin extension lead sees low voltage and runs hotter, as our guide to extension cables and electrical safety explains.
Cables, Plugs and Switches: The Parts That Shock
Brushes and bearings decide whether the tool runs. The cable, plug and switch decide whether it is safe. Check them every time you pick the tool up, because the damage is easy to see.
Look at the point where the cable enters the tool. The rubber sleeve there, the strain relief, stops the cable bending sharply at one spot. Once it splits or comes away, the cable flexes at the same point thousands of times and the conductors inside break. Look along the full length for cuts, flattened sections where it has been driven over or trapped in a door, and tape repairs. A taped cable on a power tool is a warning, not a fix. Replace the whole cable with one of the correct rating.
At the plug, check that the cable grip holds the outer sheath, not the inner wires, that nothing is scorched, and that the pins are straight. If the tool is marked with the double square symbol, it is double insulated (Class II) and is designed to be used without an earth wire. If it is not double insulated, it depends on the earth connection, so the earth wire must be connected and intact.
A trigger switch that sticks, stutters or does not cut off instantly should be replaced with the correct part. Never bypass a switch or tape a trigger down.
Bearings and Gearboxes: Listen Before You Open
Bearings and gears give their own warnings. A rising grinding or rumbling noise, a spindle you can rock from side to side, or heat concentrated at the front of the tool near the gear head all point to worn bearings or gears. A sudden metallic clatter means stop immediately.
Grease in the gearbox does break down and leak out over years of hard use. Some manufacturers specify a grease type and service interval for professional tools; follow that if your manual gives one. Bearing and gear replacement needs pullers, presses and the correct parts, so for most workshops it is a job for an authorised service centre or an experienced motor rewinder.
Storing Tools Through the Short Rains
The October to December rains bring damp air, condensation and dust turning to mud on site. Moisture on a cold motor or switch can cause tracking and short circuits, and rust attacks bearings, chucks and spindle threads. A few habits prevent most of it.
- Never use a corded tool that is wet, and never in the rain. If a tool gets wet, unplug it and let it dry fully, ideally for a day or more in a dry room, before using it again.
- Store tools indoors, off the floor, in their cases or on shelves, away from walls that get damp. A lockable cupboard does both jobs, as our guide to workshop tool storage and security explains.
- Wipe mud and cement slurry off housings, chucks and guards at the end of the day, before they set hard.
- Give exposed steel, such as chuck jaws, spindle threads and guard clamps, a light wipe with an oiled rag.
A Simple Service Routine You Can Pin on the Wall
Care works best on a schedule rather than when something goes wrong. The intervals below are a sensible starting point for tools in daily use; tools used lightly can stretch them, and the manual overrides them where it differs.
| Symptom | Likely cause | What to do |
|---|---|---|
| Loses power, cuts in and out | Worn or sticking brushes | Inspect and replace brushes as a pair |
| Ring of sparks, burning smell | Worn brushes or damaged commutator | Stop; replace brushes, then repairer if it persists |
| Very hot body after short use | Blocked vents, low voltage, overload | Blow out vents, check lead, use a larger tool |
| Grinding or rumbling noise | Worn bearings or gears | Stop and send to a service centre |
| Tingle or shock from the body | Insulation or earth fault | Stop at once; do not use until repaired |
| Switch sticks or stutters | Worn trigger switch | Replace with the correct switch |
When It Is Time for a New Tool, With Prices
Sometimes the honest answer is replacement: a burnt armature on a small tool, a cracked housing, or a tool that is simply too small for the work and keeps overheating. Matching the tool to the job is the best maintenance of all. A 4.5 inch grinder forced through heavy 9 inch work will never last, as our angle grinder guide explains. At the time of writing, these were some of the workshop tools on the Fuga price list; check the list or ask a branch for current prices and stock.
| Item | Stock code | Price |
|---|---|---|
| ANGLE GRINDER 750W | TG10711556 | KSh 4,500 |
| ANGLE GRINDER 900W | TG109125565 | KSh 5,000 |
| ANGLE GRINDER 2200W | TG12223026 | KSh 9,500 |
| IMPACT DRILL 710W | TG107136 | KSh 3,700 |
| IMPACT DRILL 850W | TG109136 | KSh 5,500 |
| ROTARY HAMMER 800W | TH308268 | KSh 7,900 |
| BRUSHLESS CORDLESS DRILL 20V(KZUBR) | 6944 | KSh 9,000 |
Unplug before you touch the brushes, replace them in pairs with the correct part, keep the vents clear of dust, check the cable every time, and stop at the first grinding noise or burning smell. Do that, and a good grinder or drill will outlast several cheap replacements. For new tools, discs and bits, browse our workshop and industrial tools or the angle grinder range, visit any Fuga branch in Eldoret, Nairobi or Nakuru, or WhatsApp 0716 961 018.
Key Takeaways
- Carbon brushes are designed to wear out so the commutator does not; replacing them is routine maintenance, not a repair.
- Loss of power, cutting in and out, or a ring of sparks with a burning smell are the usual signs of worn or sticking brushes.
- Unplug first, replace brushes as a pair with the correct part for the model, then run the tool at no load for a few minutes.
- Blow dust out of the vents after dusty work; steel and masonry dust block cooling air and wear the motor.
- Check the cable, strain relief, plug and switch every time you pick the tool up, and never use a tool with a taped or cut cable.
- Grinding noises, spindle play or a hot gear head mean worn bearings or gears, which are a job for a service centre.
- Through the short rains, never use a wet tool, and store tools dry, off the floor and wiped clean.
Frequently Asked Questions
How do I know if my grinder's carbon brushes are worn?
The tool loses power, cuts out and restarts when moved, or will not start, and sparking around the commutator becomes heavy, sometimes with a burning smell. Unplug the tool, remove the brushes and compare their length with a new brush or the wear limit in the manual.
Should I replace both carbon brushes at the same time?
Yes. Replace them as a pair, even if one looks better, so both press evenly on the commutator. Use the brush made for that model or an exact match in size, spring and lead.
Why does my power tool spark more after fitting new brushes?
New brushes have a flat face that must wear to the curve of the commutator, so sparking can be slightly heavier for the first few minutes. Run the tool with no load to bed them in. If heavy sparking continues, the commutator or armature needs a repairer.
Can I clean a power tool with water?
No. Unplug it and use compressed air or a dry, soft brush on the vents, and a damp cloth only on the outside of the housing. Never wash or spray liquid into the motor. If a tool gets wet, let it dry fully before using it again.
Is it worth repairing an old angle grinder?
Brushes, cables, switches and a clean are almost always worth doing. A burnt armature on a small, cheap tool may cost close to a new one, while the same repair on a large grinder or demolition hammer usually pays. Ask for a quote and compare it with the price of a new tool.
