Yeah, it appears to be able to move smoothly all the way with the spring force. I'd use it. The brush face is the part which contacts the commutator. So be sure to shape it to the comm diameter upon installation. I'd wrap crocus cloth around the comm and "drum sand" all 4 brushes to the comm diameter. Then use a commercially available dressing stone while running the motor at 12 volts to finish the shaping process. Then run it for hours to seat the brushes and film the comm.Hey, I wasnt sure just how free the brush was designed to move in the brush holder/guide. I shot a short video of the cleaned brush.
Let me know if you think it is moving free enough, or if I sanded too much, lol.
Got the motor appart, cleaned it up with degreaser , tarn-x, local carwash preasure wash. 800 wet sandpaper.
Thanks for taking time to look.
BTW: It has 75 bars on the communtator.
While you're going through this process, check often to see if each brush is free to move radially back and forth by pulling it up by the pigtails. If the pigtails can't withstand that much pull force, they would soon fail from a high current pulse anyway.