Key takeaways
- Carbon brushes are the cheapest wear part in a brushed circular saw and the most common reason a working saw suddenly sputters, sparks heavily, or dies mid-cut. Run them past their limit and the spring-loaded holder scrapes the copper commutator,…
Carbon brushes are the cheapest wear part in a brushed circular saw and the most common reason a working saw suddenly sputters, sparks heavily, or dies mid-cut. Run them past their limit and the spring-loaded holder scrapes the copper commutator, turning a $10 fix into a $60 to $120 armature replacement. Replace them wrong, by forcing an oversized brush into the holder or seating a new brush on a commutator black with carbon dust, and the saw arcs, runs hot, and eats the new brushes in weeks. The job takes 15 to 30 minutes with a screwdriver.
What You Need
| Item | Why | Optional? |
|---|---|---|
| Correct replacement brushes (model-specific set for Skil HD77/S77 saws about $9.99; 72-piece assorted set covering 24 sizes about $13.99) | Brush width, thickness, and length must match the holder within about 0.5 mm | No |
| Flat and Phillips screwdrivers | Remove brush caps or housing screws | No |
| Digital caliper or ruler in millimeters | Measures old brushes to confirm the replacement size | Strongly recommended |
| Compressed air or a soft brush | Clears carbon dust from the motor housing and commutator | No |
| Isopropyl alcohol (90 percent) and cotton swabs | Cleans the commutator surface without leaving residue | No |
| Needle-nose pliers | Grips brush pigtails and springs in tight housings | Yes |
| Fine sandpaper, 400 to 600 grit, or a commutator stone | Dresses a lightly scored commutator | Yes |
| Phone camera | Records wiring and spring positions before disassembly | Yes |
Step-by-Step
Step 1: Unplug and find the brush access (3 minutes)
Unplug the saw. Look on both sides of the motor housing, behind the blade guard and opposite it, for two round plastic caps about 1/2 to 3/4 inch across or two small covers held by a screw. Saws with external caps take five minutes; saws without them require removing the rear motor housing, typically 4 to 6 screws. Photograph the housing before opening it.
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Step 2: Remove the old brushes (5 minutes)
Unscrew each cap and let the spring push the brush partway out; catch it so it does not shoot across the shop. On internal designs, unclip the spring arm and lift the brush from its brass holder, then unplug or unscrew the pigtail wire from its terminal. Note which brush came from which side and how the beveled contact face was oriented, since brushes wear to match the commutator’s curve.
Step 3: Measure and compare (5 minutes)
Measure the old brush’s width and thickness; common circular saw sizes are 6 x 10 mm, 6.5 x 13.5 mm, and 7 x 17 mm, with new lengths of 16 to 20 mm. A brush worn to about 1/4 inch (6 mm) or to the wear line is due. The new brush should match within 0.5 mm in width and thickness with the same pigtail length and terminal shape, and it must slide into the holder freely under its own weight.
Step 4: Inspect and clean the commutator (5 minutes)
Shine a light into the brush holder at the copper commutator segments. They should be a uniform light brown, which is the normal film, with clean grooves between segments. Blow out carbon dust and wipe the copper with an alcohol-dampened swab, rotating the blade by hand with the saw unplugged to reach the whole surface. Black streaks, deep grooves you can feel with a fingernail, a segment sitting higher than its neighbors, or a burnt smell mean the armature is damaged; new brushes will not fix that.
Step 5: Dress light scoring if needed (5 minutes)
If the copper shows fine scratches but no grooves, hold a strip of 600 grit sandpaper lightly against the commutator while rotating the blade by hand for 10 to 20 turns. Blow out the dust and wipe again with alcohol. Do not use emery cloth; its conductive grit embeds in the copper and causes arcing.
Step 6: Install the new brushes (5 minutes)
Slide each brush into its holder with the curved contact face matching the commutator’s curve and the pigtail routed the way the old one ran. Connect the terminal, seat the spring so it presses squarely on the back of the brush, and replace the cap or spring clip. On capped designs, thread the cap until it is snug, not tight; cracked caps are a common side effect of overtightening. Reassemble any housing.
Step 7: Seat the brushes with a no-load run (5 minutes)
Plug in and run the saw with no blade load for 3 to 5 minutes in bursts of 30 seconds, letting it rest between. Expect light sparking at the brushes for the first minute as the flat new faces wear to the commutator’s curve. Heavy, continuous sparking or a burning smell means a brush is undersized, misaligned, or the commutator is damaged; stop and recheck. Make a few light test cuts before returning to full-depth work.
Mistakes to Avoid
Filing or sanding a too-large brush to fit, which leaves it loose and arcing. Replacing only one brush; they wear as a pair. Installing brushes with the bevel facing the wrong direction. Skipping the commutator cleaning. Using emery cloth on copper. Overtightening plastic caps. Running the saw under full load immediately without seating the brushes. Mixing up pigtail terminals on saws where the wires are different lengths.
How Often
Check brush length every 50 to 100 hours of use, which for a homeowner is every year or two. Replace when they reach 1/4 inch or the wear mark, or immediately if the saw develops intermittent power, heavy sparking visible through the vents, or a drop in speed under load. Many saws have an auto-stop brush that cuts power when worn; if a saw dies suddenly with no smell of burning, brushes are the first suspect. Blow out the motor vents after every dusty session, since fine sawdust mixed with carbon dust is what scores commutators.
When to Call a Pro or Replace
Take the saw to a repair shop, typically $40 to $90 in labor, when the commutator is grooved deeper than about 0.5 mm, a segment is raised, the armature smells burnt, or the saw still sparks heavily after correctly sized brushes are seated. An armature runs $50 to $150 in parts. Replace the saw when repair approaches half the price of a new one, which for a $60 to $100 sidewinder is almost immediately; worm-drive and premium saws are worth repairing. Brushes for common saws still cost under $15 a pair in 2026, so a well-kept brushed saw runs for decades on a few dollars of maintenance.
FAQ
How do I know the carbon brushes are worn out?
The saw loses power under load, sparks brightly through the vents, runs intermittently, or stops entirely while the cord and switch test fine. Pull a brush and measure; anything under 1/4 inch or at the wear line is done.
Can I use generic brushes from an assortment kit?
Yes, if the width and thickness match within 0.5 mm and the pigtail terminal fits. An assortment is a good backup for older saws with no factory parts available, but a model-specific set is the safer first choice.
Why are my new brushes sparking?
Light sparking during the first few minutes is normal seating. Continuous heavy sparking means the brush is loose in the holder, the spring is not pressing squarely, the commutator is dirty or scored, or the brush grade is wrong for the motor.
Do brushless circular saws need this?
No. Brushless motors use electronic switching instead of carbon brushes, so there is nothing to replace. They cost more up front but eliminate this maintenance entirely.
