Many hobbyists and model builders use the Dremel 4000. It not only packs the punch of the original Dremel rotary tool, its high-performance motor also drives additional attachments such as the Dremel Multi-Saw in the Dremel Planer as well as a seemingly unlimited number of Dremel bits. The tool also seems to be quite durable. From time to time though, even this iron horse will break down. When the motor stops running, it is usually because the brushes are worn.
Unplug the Dremel 4000 rotary tool, and place the tool on a clean surface.
Remove the brush cap located on the top of the tool by inserting the screwdriver end of the collet wrench into the slot on the brush cap and turning the cap counterclockwise until the brush cap is completely removed.
Remove the top brush by pulling it out using the brush spring. Insert a new brush where the old one was removed, making sure the curved side of the new brush matches the curvature of the commutator on the motor, and the spring faces away from the motor.
Thread the brush cap back into the Dremel 4000 clockwise, and tighten the cap using the screwdriver end of the collet wrench.
Repeat the procedure for the brush located on the bottom of the tool.
Plug the tool in and run it for five minutes at full speed to make sure the brushes properly seat on the motor commutator, completing the repair of the Dremel 4000.