Most Common Alternator Fail = Brushes?

[ajbremer]

1989 Bronco II XLT:

Found out I'm not charging so I had my alternator check at O'rielly's and it was bad. Got a used one at a yard for $35. Got them home and noticed that the one I got at the yard had a clicking noise at each rotation, not a good sign. So I thought I would just switch out the (internal) voltage regular. I first removed the VR from the original Bronco 'bad' alternator and found they were almost worn down to nothing. Then I removed the VR from the alternator I just got from the yard, they were a little better but worn down also. So...I put the VR from the yard into the original 'bad' alternator and will install it to see if it'll work.

I noticed that I can purchase a new alternator brush kit from the auto parts store for only around $5.00 and I'm wondering if those brushes are mostly the same size. I measured mine and they are .155 x .295.

I've included a pic of the original brushes.

All this leads me to my main question: Do alternators fail mostly due to worn brushes and brush problems?

 

[Tiha]

Looks like that brush got stuck at some point. rebuilding is a lost art. Too bad. I hate throwing things away.

Failures depend on a lot of things. If the brushes are worn out. If it made it that far, then the alternator has had a good long life already.
Diodes, Voltage regulators now a days are the main causes of failures. I guess bearings too. They don't seem to last either.

Sounds like it is worth a shot for ya. Hardest part is, for the average everyday guy like us we can't really test the armature.

 

[miesk5]

Yo AJ,

System Does Not Charge

Battery connections., especially grounds Drive belt. Battery drain. Open/voltage drop . Open circuit. Open/high resistance in circuit. Voltage regulator..

 

[Motech]

Lately (last decade) I've seen internally shorted battery cells causing a lot of alternator failures, particularly among certain battery brands. It's not an obvious condition, but can be revealed with a voltmeter and inductive amp meter.

When plates become internally shorted, an artificially high current demand is placed upon alternator. Charging voltage will be low at around 13.7 to 13.9 (14.1 to 14.2 is normal), and idle amperage output will be high, usually a constant 25 amps that does not come down with extended idling. (25 amps is normal if battery has been loaded, but should drop to under 10 amps after a few minutes of unloaded idling)

Again, little tricky to spot, and it does overtax an alternator, causing pretty rapid failure of high-mileage and cut-rate replacement units.

It is worth it to have an inductive amp meter in your tool set, even simple (and affordable!) units like these: