My little Ranger has passed 185K miles. I've never had a problem with the alternator, but I know one of the components that wears out is the brushes. I believe that replacing the brushes
in the alternator can eliminate a lot of expensive alternator replacements. The procedure below goes over the steps to replace the brushes while the alternator is left on the vehicle. As you
can see from the photos, there wasn't much left on one of the brushes.



1) Remove negative battery cable:




2) Remove heater hoses at firewall:




3) Tools needed to remove alternator voltage regulator / brush assembly:








4) Remove 4 TORX screws holding alternator voltage regulator / brush assembly on the back of alternator. The 2 upper screws are circled in RED:




5) Old brushes:








6) New brushes:








7) Remove insulator cap:




8) Remove TORX screws holding brushes to voltage regulator:




9) Old vs New brushes:




10) Install voltage regulator / brush assembly back on alternator. Make sure to remove brushes retainer pin:

 

Uneven heat dissipation over time causes one spring to become softer.
Also there may be a microscopic rough spot on the armature having a sandpaper effect.

DC motors on the other hand will always wear the negative brush more than the positive side.Since electron flow (current) actually flows from negative toward positive , contrary to popular understanding , the electrons pull some of the carbon material with them.

 

Correct, it is the current polarity that makes 1 brush wear faster than the other. You can also see the effect if current polarity on the spark plug post in the photography forum. The plugs in the passenger's bank has the GND electrode worn, while the plugs in the driver's bank has the center electrode worn more.

 

I just replaced my alternator today (had shop do it, was $135 for parts/labor), and he pulled out the brushes to check them, and there was NOTHING left on them.

I had been experiencing random voltage drops from alternator last few days, almost stranding me on highway when alternator stopped charging completely at one point.

 

Have been unable to find these alternator brushes. Are they called something else? Autozone does not list them on their site.

 

The brushes and housing are called an: Alternator Brush Assembly. I got it from NAPA, give your local NAPA dealer
the P/N, and they should be ablt to get it for you.

 

For brush sets, look at Rock Auto. Better price. Also the brushes need to be seated to match the slip ring contour. Use sand paper, not wet or dry.