Fantastic explanations, thank you gentlemen.

On occasion, a repair I make to this vehicle feels arbitrary... I always have a difficult time with that. I’m now happy to remove the old alternator for a thorough inspection, regardless of whether I use the new one.

Again, thank you for taking the time.

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1981 240D 4sp manual. Ivory White.

The groove in the slip rings is often overlooked when doing a routine DIY regulator repair resulting in one or both brushes riding incorrectly and causing rapid wear of the slip rings runing them .

I've had no issues with bleed through ever but as often mentioned "your mileage may vary" .

I've had very good luck in hand polishing slip rings and new brushes .

Maybe, if this one spins with zero bearing vibration / feel / noise, clean it and install new V.R. and save it .

I too use an electric impact, using the hand impact you smack with a hammer is bad for the bearings .

Thrift stores are good places to get expen$ive tools like electric impacts cheaply ~ just TEST THEM FIRST and never forget : the replacement batteries are usually more than the tool cost new, why I don't buy battery powered tools ~ they're only co$t effective if you're going to use them a lot .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I actually have a bunch of Ryobi tools, but only a couple of batteries and a single charger. I add to my collection of tools at garage sales and flea markets, and buy a new battery very rarely. Staying in the same "battery family" makes it very cost effective.

Just pulled the old alternator. The grooves are minuscule... I’d say a quarter to half of a mm.
With the voltage regulator removed, the pulley spins freely. However, I can hear what I assume to be a light bearing noise.

Should the spinning be totally silent?

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1981 240D 4sp manual. Ivory White.

The bearings may be a bit worn, hard to say without tearing it down.

If you hear /feel any bearing noise / rumble they're kaput .

I'd say junk it .

I may have a good spare one but I suggest going to Pick A part and buying a BOSCH branded rebuilt to keep for your own spare....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better