New BMW/Bosch brushes will usually measure 16.5 mm (0.655") as measured from flat top to middle of the curved portion.
Worn out is below 8mm or so.
Most important for side-of-the-road fixing is that the brush spring is not contacting the plastic mount, in other words the spring is still pushing on the brush not bottomed out on the mount.
Replace the spring as well as the brush if possible. It may also be time to just rebuild the whole thing. Take it to most any starter motor repair shop (automotive) and they can do a full rebuild and check for probably under US$50.
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Grant Johnson
Share the Dream!
at: www.HorizonsUnlimited.com
__________________
Grant Johnson
Seek, and ye shall find.
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Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com
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