How to Repair a Brushfull Motor

About: Engineer making renewable energy products for African entrepreneurs.

Have a brushfull motor making a clanking grinding sound of death? It's likely one of the brushes have come out of the their tracks and needs to be reset.

You'll likely find that these motors are easy to take apart, and terribly difficult to put together - requiring custom tools and a little coaxing.

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Step 1: Take Apart Motor

Remove any case screws and set aside - then pull the back cover away from the motor housing. If your brushes are spring loaded (like this motor's), they may spring apart. Remove the casing slowly to prevent any rogue springs from disappearing under your work bench.

Step 2: Inspection

Look at the motor's innards. Look for physical damage, scorching etc. If you don't find anything, look for free fragments of anything. The case magnets should not touch anything except the motor housing.

If everything looks good, take a look at the brushes. They should have a concave portion on one end where they touch the motor armature.

If everything looks good, we'll hope that the brushes just need to be reset.

Step 3: Custom Tools

In my case, my brushes are spring loaded... And don't like to stay in place. So, you'll need to make a holder that you can remove once the armature is in place. The brush holder have a small hole in the side - perfect for a small paper clip.

Push the spring and brush assembly into it's holder.
  • use a small screwdriver to push the spring into the holder (there's a channel on the side for this)
  • push the brush into the holder while holding the spring back
  • insert a bent paper clip through the small hole

Repeat for all of your brushes

Step 4: Assemble Motor

Now it's time to complete assembly.

Lower the motor housing onto the paperclipped rear casing. Be sure the tightening screws line up.

Now, pull the paper clips out of the housing. The brushes should gently push up against the armature (you shouldn't here loud clicking or similar).

Screw your motor back together and make sure the shaft spins freely.

Now test. The first time I gave it power, my leads had a rather large spark. The second time it powered on without problem :)

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    11 Discussions


    9 years ago on Introduction

    My hubs brought home a practically brand new table saw from work the other day that just quit. It took DAYS to get the dang thing apart and access the motor, and meanwhile searching the web for solutions, I ran across a forum that mentioned the brushes, then today an ible that mentioned the power switch. Nothing looked "scorched" in or around the motor as well as the switch, but, when I pulled the brushes out, I noticed that 1 was chipped slightly along 1 corner. The brushes for this particular saw are the ones that have the ferrite block molded around a naked stranded wired inside a spring with a brass clip, and are super cheap, but I was wondering if there was anyway to grind down the surface of the ferrite cube a tad or some other way to bring these brushes back to life? They look to have very little other wear, no scorching, fraying, or damage. Just a thought, not just for this tool, but if I run into similar issues in other tools in the future. You mentioned in your ible that "upon inspection, everything looked fine and hopefully all it needs is to reset the brushes"...could you define "looks fine" and explain resetting the brushes. What I mean is, if the innards looked fine and the brushes didn't need replacement, then why did the motor shut down? Can brushes slip out of alignment during normal use and simply need to be pulled out and "reset" into alignment again? I hope these Qs aren't too elementary. I'm still green, but eager and appreciate any information your giving. Thanks, Teri : )


    11 years ago on Introduction

    Excellent information here and great idea using the paper clips. They fit perfectly. The other day I was driving down the street and noticed someone was throwing out a Razor Mini Chopper. I immediately threw it in the car. When I got home I saw that it had the charger hooked to it. How lucky could I be? I started testing the components out. Using a multimeter I began testing the voltage. Everything works and the motor is getting adequate voltage but the motor did not spin. This did not make any noise like most troubleshooting tips state. So I took the motor off and apart. I cleaned the springs, brushes, guides and contacts. One of the brushes was cracked. For this I used a little epoxy by placing the wire in and making a cap of epoxy being careful not to insulate the connection. I used a little CLP gun oil to lightly lubricate the parts and provide long term protection. Later that night I looked up replacement parts and found they're fairly cheap. A new motor is around $30. The next day I assembled the motor using the paper clips to hold the brushes in place. About a 2 minute total reassembling time and I was done. Before bolting the motor back to the chassis I tested it out by providing 12VDC and verified that it worked. The Mini Chopper works great.

    2 replies

    Reply 10 years ago on Introduction

    Be warned that by epoxying a cracked brush instead of replacing it, that you are fouling the commutator, and actually wearing it away at an accelerated rate. The epoxy will wear on the commutator, and the heat from the defective brush will burn a lacquer onto the commutator, and increase resistance. This wil result in the burning of the commutator and the accelerated wear of all brushes, as they now have a more difficult time making a clean connection. Arcing will slowly destroy the commutator, rendering the motor irreparably-damaged. If you added oil to the brushes, you accelerated the problem, as no motor brush should be contaminated with oil, due to the fouling that would occur and again damage the commutator.


    Reply 9 years ago on Introduction

    Thanks I had no idea. Do you have a source for obtaining prewired brushes? I had no idea what to do then. I used the CLP because it contains Teflon and the oil was almost non-existent when re-assembled. The motor still runs almost 2 years later. 


    10 years ago on Step 3

    One of my brushes keeps getting stuck. the spring looks pretty well destroyed. This causes the brush to arc out on the side of it's casing. Anyone know where I might obtain a new spring. House hold materials that might contain one?


    10 years ago on Step 2

    hi there,would it be possible to remove the insides ,so your just left with the outta casing?? thanks


    10 years ago on Introduction

    That commutator is in bad shape from the pic you gave...It needs a cleaning with a pencil-eraser, and then lathing-and-honing to make it square again. If you look closely, the segments are "ramped", and likely due to an improper break-in and.or poor motor design..."Erase" the carbon from each segment in a lateral direction (parallel to rotation) with the pink pencil-eraser until each segment is clean. Take a piece of clean copy/typing paper or paperboard and rotate the rotor as you hold the paper like a band-brake on the commutator. Do this until the paper comes out clean. Wash with contact-cleaner, then run the motor at no load for at least an hour. If you can use another motor to spin it externally, that would be ideal, and then run the motor no-load for at least an hour afterward. By then the brushes should be quiet and perfectly-seated for an ideal connection. By breaking in the motor properly, you can extend brush-life by at least 30%. Make sure that motor brushes NEVER come in contact with oil or any other contaminant. However, "Cramolin" aerosol is an approved contact cleaner and lubricant. If you don't have it, use nothing else on the commutator other than an electrical contact-cleaner. to clean it. We've done flame-battles in the past, but this I give to you in earnest. The clean leading-edge that is significantly smaller than the carbonized trailing-edge of the commutator segments suggests significant arcing at the brushes. To prolong the life of the brushes and commutator (basically the motor itself), this must be corrected as soon as possible. Otherwise, this motor will eat brushes like crazy and be a persistent annoyance in terms of maintenance, as well as a loss of overall efficiency that can be as high as 30%.