Alternator whining on charge only

[Titan1969]

thx in advance. I have a '73 340 Cuda with a alternator that only whines when charging.

Sounds like "WRRRRRR" then goes silent then repeat.

Its definitely not a bearing as when I turn on headlights, the WRRRR is constant. It does charge ok.

Should I just buy a new 60 amp alternator? or could this just need some new brushes/diodes to fix it up like new?

Id rather tinker and fix then buy new just for the fun of it, but dont want to mess anything up and get stranded with a bad alternator.

 

[Chryco Psycho]

New is not nessisarily better , I would either swap in another original alt usually easy to locate or take it to a rebuilder to have it checked out , probably a simple fix .

 

[fasjac]

If you haven’t already, check the charging system with your multimeter. Maybe under a big load it’s howling/whining. ?? Battery getting too weak?? Etc JMO

 

[Titan1969]

its new battery, holds 12volts when not charging and jumps to 13.5-14v when running. no other electronics, not even a radio.

 

[NoCar340]

I'd say it's a bearing. When charging, the armature and field coils are producing strong moving magnetic fields. Those create additional loads on the bearings due to magnetic attraction and repulsion, and those forces are greater according to draw. Headlamps are a huge draw, hence the constant noise. When it's loaded lightly, the armature freewheels on unloaded bearings.

Ever have a wheel bearing that only made noise when turning? It's sort of the same thing.

You could try replacing brushes since they're cheap and easy, but I think you'll need either new bearings or a replacement alternator.

 

[Titan1969]

ah ok that makes sense. The car was a 20+ resto project, was not driven since early 90s and the alternator is older than that.