Bearings and cleaning will not fix an electrical problem such as bad diodes, bad stator or rotor windings, diodes, etc. Voltage drop can also be load related especially at low engine speeds such as when idling. Most likely the squealing belt is the main source of your problem. As a simple test you should be able to use a wrench on the alternator pulley and turn the engine over including past the compression strokes. The alternator belt needs to transmit somewhere between 1-2 horsepower into it. The starter motor is less than 1HP. This is a challenge as the belt wrap around the drive pulley is less than 90 degrees. An ideal belt design would be 180. A loose belt can be more destructive than an over tightened one due to the oscillations that go with it. Especially for the brackets. A belt tension gauge is a good investment here. 

Dennis
 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of T Collins
Sent: Monday, December 1, 2014 9:50 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Alternator rebuild

Hello list,

Has anyone rebuilt a 90A bosch alternator? Symptoms: Drop in voltage at times, squealing sound like a belt struggling. voltage regulator brushes look good.

Is this as simple (or not) as replacing the 2 bearings in the alternator and cleaning things up?

Advice is greatly appreciated.

Thanks,
T.