You can scrape, file or sandpaper the brush material away very easily. It just makes a pile of carbon dust, and if you try this and then you need a new one!  So don't!  It also makes it trivial in an emergency to fit the brush from a current powerchair into an old no longer made one that parts are unavailable for. A little careful selection, and a file and it can be done.

Brushes transfer the POWER (from your batteries via the controller) to the motors rotating internals. They do this by riding on a segmented copper thing called a Commutator.   Shown below.

This it the part that spins inside your motor and that the Motor's brushes (that we will be examining) run on. A spring provides some pressure. They are free to move as they wear to maintain contact. They provide up to 120 amps of power in a modern powerchair to this copper "ring".

Usually the faster / bigger Powerchair has 4 brushes on each Commutator. Its called a 4 pole motor. Smaller powerchairs use 2 pole motors which tend to eat brushes faster in my experience.

Two brushes above. One is shorter than the other due to wear/arcing and use. All four from this motor were the same, and worn out... The longer one is a NEW one shown as a comparison.  You need a new one to compare the length.  These though are actually from two different "years" of the same motor.  The cleaner and longer one is the replacement.  Also examine the "tip" for burning, and chips or bits missing and pitting.  Obviously the shorter one is absolutely knackered here! I check and swap mine as needed. Worn brushes eventually cause breakdown, and damage to the armature from arcing as the spring pressure is then too low.

As brushes "run in or break in" they "wear" and conform to the curved shape of the commutator. Actually they more "burn in" to begin with due to the small contact area of the new "square" ended brush. So it pays to go steady and avoid heavy loads like ramps and hills for a few days with a new powerchair. If you have the patience!

When new they are generally just square ended like the new one seen above. But once bedded in they have a "curve" that perfectly matches the commutator (WAY above!) as you can see in this close up picture below. And all the tiny grooves in its surface match too. The commutator also wears as it runs as well but does so much slower. This brush  below is perfect with no burning (arcing) or any real wear or other damage or chips or pits.  Pits and chips actually happen due to arcing as these things have a very large current going through them at times depending on chair and user!

Its just 5mm shorter than the brand new one.  If it was 8 to 10mm shorter it would go in the bin. It can only go into the motor one way due to the design of the brush "holder" shown later. It fits into a rectangular slot, (below) It therefore sits in "exactly" the same position (as it should) as it did before it was ever removed. It cant really do any other. This one will go back in as its perfect.

On some motors it is possible to replace the brushes in "reversed" and although its not that detrimental, it's still best to make a note of which one went where and its orientation. Its because of those tiny grooves you can see and the exact angle of the "worn in" end.  If you get it wrong it will soon "wear in" again regardless as its soft. You will not notice any real difference. But that "wearing in" takes a very small amount of material away and shortens the life a little! Likely you wont care once you see how easy they are to swap and they are pretty cheap too.

They continue to wear / burn away slowly throughout the life of the powerchair. Brushes are like brake pads for your car, they are considered as items that are replaceable. That's why your powerchair manufacturer carries these as a spare and why you can swap them in minutes in situ. 

Although they are generally good enough to last many thousands of hours with an average user on average terrain with average programming. If that's you and you have a quality branded powerchair with no odd noises then don't bother checking them for about 3 to 4 years! 

However, if you have a some attitude, do Powerchair basketball, football, etc. And if you REALLY USE and hammer your powerchair to the extent that a set of batteries will last you about a year or less then check them yearly! And or you do hills, ramps, off road, winter, and especially if your chair is programmed to get the most possible out of it then it also pays to check yearly!   You see not everyone is the same. The ones in my chairs are about half worn after 12 months of the kind of daily abuse I give them... If this sounds like you it would pay to remove the brushes (takes just minutes on many powerchairs) and to examine them.

The manufacturers see no problems with brushes since the average user sits about, doesn't go off road, on beaches, or discharge a set of batteries almost completely every single day.  Normally they sit at a desk, or at a computer all day, or in front of the fire. If they do "go out", they are not aggressive and do it only a few times a week and don't go very far.  If you do USE yours, then you are outnumbered by about 1000 to 1 and considered an aberration!  You are not part of their figures.

You do not need to disassemble your motor!!!  This was just an old dead abused 2  pole one that was going in a "robotic" vehicle.

Looks like new. But not a waste of time since these motors were sold to a friend. (I don't want to sell a set of motors to someone without knowing they are still good to go!  I also blew out all the dust, checked the bearings, the gearbox backlash and the Cush drive/motor coupling while I had chance.  And tested them on a battery. (Reason? Unknown history!)

Closer  Needs the dust blowing out, the brushes wiping on a cloth (they were coated in dust that made them not slide freely as they are supposed to do.  Then put all 8 back into both motors IN THE SAME POSITIONS, AND THE SAME WAY AROUND as you took them out. Mark them with a CD writing pen with an arrow and a number. Write the same number on the motor.

This is the same brush.  And the slide out cap.  Its only fault was the carbon that was jamming it. See the chamfer on the long edge facing you? You can see some of the carbon along there that I have not yet removed. There is just a few mm missing from this brush so I will put it back! That black carbon is on my bed! GF pleased.

Of course you must have a new one to compare it too. Or at least a measurement! But if you go to the trouble of taking them out it makes sense you have some spares just in case.

I check all my powerchairs regularly. I log the brush length against the powerchairs "hours" to give me some idea how long they will last this year! But I am an animal and put more amps through these brushes than they were actually designed for.

An alternative brush cap.