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Alternator questions

grandpa Love

grandpa Love

Well-known Member
Ok.... So I've got a pile of 'bad '
alternators, what goes bad in them???
Bearings are quiet, Google says that's
the most common issue.
 
Diodes and brushes as Steve suggests. Occasionally also the regulator on internally regulated (Delco xxSI family) alternators.

And I've encountered a few where a stator coil circuit went open. The alternators still worked though with dramatically reduced (by about 70%) current output.
 
Go on Youtube, look up 'Rebuilding a Delco Alternator', I'm sure there are plenty of videos.

Usually the diode trio goes out. That will reduce the output.

The rectifier can burn out, usually a result of connecting the battery backward or running with a dead/shorted battery.

The windings can also short or burn out, also from running with a dead battery or being packed with dirt and under heavy load, or too small alternator for the demand.

Brushes, my theory... If the brushes are worn to the point of being gone, so short they popped out of the holder, there is a reason, a shorted stator overloaded them. Every time I have encountered this, new brushes did not fix it!

You do know the trick to get the brushes back in? A straightened-out paper clip through the hole to hold them in.

Also pay close attention to where the screws and insulating washers go that hold in the regulator and brush holder. They must go in the right places. Often that is why an alternator is not working, someone has had it apart before!
 
Brushes, diodes and bearings are the most common problems. I've had a few 10SIs that I would polish up the slip rings and new brushes if needed about every year.
 
Diode trio is usually the culprit on most all I have repaired. Sometimes the regulator. I polish the slip rings and reuse the brushes most times. The diode trio used to be around 6 bucks but the regulator was about 17. Test the diode trio with a test light and a battery. All three legs should pass current one direction and none the other direction. The regulator test requires a battery and a fast charger and a volt meter.
 
the older 10SI's would short the diode trio. I think hooking up
a jump start +/- incorrectly would get 'em. Symptom would be to run the battery down after shut off.
Also have had an alternator bearing set up going across a bridge.
Had to continue with the belt squealing.
On the same subject..........
Has anyone had any experience with the new 6 Volt Positive ground regulator that
has recently become available for Delco alternators? Ran across a reference to it on the Model A site.
 
You got good advice below. If they are one wire alternators I have found the regulator to often be the issue. I think the alternator on my Farm-All 400 failed at least three times before I converted it back to two wire. You can change back to a two wire by changing the regulator, likewise you can convert to a one wire by installing a one wire regulator. Over the years I have successfully rebuilt several alternators. If you are not installing new brushes be very careful when separating the body, it is fairly easy to damage the brush holder.
 
There's more to converting one to positive ground than just a regulator.

It would need a reversed rectifier and diode trio also.
 
A bit off the topic: A number of years ago, I had a Chevy station wagon. The alternator quit.
I was so broke; I couldn't afford to pay attention (Mechanic for a Case tractor dealer).
As I was lamenting what to do, I was looking in a 2090 Case tractor book for something.
I happened upon the Electrical section. There it told how to disassemble the alternator (same brand as on my car)
and check the various components with a DVOM. So, I took my alternator apart and checked it out. Some of the
DVOM values were different but were close enough to determine if the part was bad or not.
I put in (at the time) a $5 or $6 triode and it went to work. Saved me bunches of $$$!!!
 
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