What electric motor brushes do and why they wear out

Electric motor brushes are small carbon or graphite blocks that sit inside an electric motor and press against a spinning part called the commutator. As the motor runs, the brushes deliver electrical current to the commutator, which switches the current direction many times per second to keep the motor spinning. This constant contact and switching creates friction and wear — brushes gradually thin out and eventually stop making good contact with the commutator.

The wear rate depends on how hard the motor works, how often it runs, and the quality of the brushes themselves. A drill used occasionally might have brushes last for years. A shop tool running eight hours a day might need new brushes every few months. When brushes wear down too far, the motor loses power, runs roughly, or stops working altogether.

Not all electric motors use brushes. Brushless motors use electronics instead of brushes to switch current direction, which is why they last longer and need less maintenance. But many common tools — drills, angle grinders, circular saws, impact drivers, and older shop equipment — still use brush motors because they are cheaper to make and repair.

Key Takeaways

  • Brushes transfer electrical current to the spinning commutator inside a motor and wear down from friction over time.
  • Signs of worn brushes include loss of power, rough running, visible sparking inside the motor, or a burning smell.
  • Brush replacement is one of the cheapest motor repairs and usually costs between $20 and $100 in parts, depending on the motor type.
  • Brushes typically last longer when the motor runs at steady load rather than starting and stopping repeatedly.
  • Some motors are not worth repairing once brushes wear out; comparing replacement cost to a new tool helps you decide.

Signs that brushes are wearing out

The first sign is usually a loss of power or speed. The motor still runs but feels weaker than it used to, or a drill spins slower even when the battery is fully charged. This happens because worn brushes make poor contact with the commutator, so less current reaches the motor windings.

Visible sparking inside the motor is another clear signal. If you look into the air vents on the motor housing and see bright flashes, the brushes are likely worn unevenly or the commutator is dirty. Some sparking is normal, but heavy sparking means the brushes are near the end of their life.

A burning smell or visible carbon dust around the motor vents also points to brush wear. As brushes wear, they shed carbon particles that can build up inside the motor. If the smell is sharp or chemical rather than just burnt carbon, the motor windings themselves may be damaged, which is a bigger problem than brush wear alone.

Rough running or vibration that was not there before can mean brushes are worn unevenly, so they make contact at different times as the commutator spins. The motor may also make a grinding or chattering sound.

How to replace brushes in a typical electric motor

Brush replacement varies by motor design, but the basic steps are similar. First, unplug the tool or disconnect the battery. Then remove the motor housing — usually held by a few bolts or screws. You will see the commutator in the center, a cylinder with grooves running along it, and the brushes pressing against it from the sides.

The brushes sit in metal holders called brush holders or brush caps, often held in place by a spring. Slide or unclip the old brush out, noting which way it faced. Slide the new brush in the same way, making sure the spring still pushes it firmly against the commutator. The brush should move freely in its holder without rattling.

Before reassembling, wipe the commutator clean with a dry cloth or a cloth barely dampened with electrical contact cleaner. Dirt and carbon buildup on the commutator will wear new brushes faster. Reassemble the motor housing, making sure all wires are in their original positions and nothing is pinched.

If you are not comfortable opening the motor, a repair shop can do this work in an hour or less. The labor cost is usually $30 to $60, plus the cost of brushes.

Brush types and how they affect motor life

Brushes come in different grades. Carbon brushes are the cheapest and work well for light to medium use. Graphite brushes conduct electricity better and last longer, making them worth the extra cost for tools you use regularly. Copper-graphite brushes are the most durable and are used in heavy-duty industrial motors, but they cost more and are overkill for most home tools.

The commutator surface also matters. A smooth, clean commutator lets brushes make even contact and wear evenly. A pitted or grooved commutator forces brushes to wear unevenly and fail faster. If the commutator is damaged, it can sometimes be resurfaced by a motor repair shop, but the cost may exceed the value of the tool.

Brush pressure — how hard the spring pushes the brush against the commutator — is set by the motor design and should not be adjusted unless you know what you are doing. Too little pressure and the motor loses power. Too much pressure and brushes wear out in weeks.

When to repair versus replace the whole motor or tool

A new set of brushes costs $15 to $40 depending on the motor size and type. Labor at a repair shop adds another $30 to $60. For a drill or saw you use regularly, this is almost always worth doing.

But if the motor is old, the tool is cheap, or other parts are also failing, replacement might make more sense. A new basic drill costs $50 to $150, and a new motor for a larger tool might cost $100 to $300. If brush replacement plus any other needed repairs approaches half the cost of a new tool, buying new is often the better choice.

Also consider whether you can live without the tool while it is being repaired. If you need it for work, the downtime cost might tip the decision toward replacement. If it is a backup tool you use occasionally, repair is almost always cheaper.

How to extend brush life

Run the motor at steady load rather than starting and stopping repeatedly. Each time a motor starts, it draws a large current spike that stresses the brushes. Continuous running at moderate load is gentler on brushes than frequent on-off cycles.

Keep the motor cool. Brushes wear faster when the motor overheats. Make sure air vents are not blocked, and give the tool breaks if it gets hot. Do not run a corded drill or saw continuously for more than 15 or 20 minutes without letting it cool.

Keep the commutator clean. Dust and carbon buildup force brushes to work harder and wear faster. Blow out the motor vents with compressed air every few months if you use the tool regularly. If you see heavy carbon dust, open the motor and wipe the commutator with a dry cloth.

Use the right tool for the job. Running a small drill at full power to drive large bolts stresses the motor and wears brushes faster. A larger tool or a different approach uses less current and extends brush life.

Brushless motors as an alternative

Brushless electric motors use electronic circuits instead of brushes to switch current direction. They have no brushes to wear out, run cooler, and last much longer — often two to three times as long as brush motors. They are also more efficient, so batteries last longer on cordless tools.

The trade-off is cost. A brushless drill costs $50 to $150 more than an equivalent brush drill. For occasional use, the extra cost may not be worth it. For regular work, the longer life and lower maintenance often pay for themselves within a few years.

If you are buying a new cordless tool and plan to use it often, brushless is usually the better choice. If you already own a brush motor tool and it works well, there is no reason to replace it just because brushes eventually wear out — replacement is cheap and straightforward.

Frequently Asked Questions

Can I run a motor with worn brushes, or will it damage the motor?

Running a motor with very worn brushes will not when ready destroy it, but it will overheat and lose power. The commutator may become pitted or scorched, which makes it harder to repair later. It is better to replace brushes as soon as you notice power loss or heavy sparking.

How often do brushes need replacing?

It depends on use. A drill used a few times a month might go years without needing brushes. A shop tool running daily might need them every six months to a year. There is no fixed schedule — replace them when you see signs of wear.

Do I need special tools to replace brushes?

You need a screwdriver or wrench to open the motor housing and remove the old brushes. A cloth to clean the commutator is helpful. You do not need expensive equipment. A repair shop has the right tools and can do the job quickly if you are not comfortable doing it yourself.

What is the difference between carbon and graphite brushes?

Graphite brushes conduct electricity better and last longer than carbon brushes, but they cost more. For tools you use regularly, graphite is worth the extra cost. For occasional use, carbon brushes are fine.

Can a damaged commutator be fixed without replacing the whole motor?

A motor repair shop can sometimes resurface a pitted commutator on a lathe, but the cost is usually $50 to $150. If the commutator is deeply scored or burnt, resurfacing may not help. Compare the repair cost to the cost of a new motor or tool before deciding.