alternator or voltage regulator
 

83 300 d would not turn over. happened suddenly. battery showed 11.9 volts. jumped the bugger and had 12.8 -13. volts at idle. no load. with the high beams on i had something like 12.4 volts at idle. increasing engine speed did not seem to cause the voltage readings to change. my question. alternator or voltage regulator? as an aside battery treminals are corrosion free and i have a good ground. thank you.

More likely to be the regulator. Pull it out (two screws) and look at the brushes, I bet they're worn out. If you can afford it, you could just spring for a rebuilt alternator, but I'd start with the regulator.... as long as the slip rings aren't badly grooved it is highly unlikely the alternator itself has failed & needs replacement.

Janko.

Probably the brushes are worn out. You can get them out along with the regulator with out removing the alternator off. If brushes are bad, just replace them.

I replaced the brushes in my alternator 12 years and 125,000 miles ago and its still working. Its probably due for another set of brushes soon and I will replace them again when necessary. No sense replacing the alternator when only the brushed are worn out. That's like replacing the rear suspension when all that is wrong is a flat tire.

P E H

I'm almost positive the brushes are not replaceable separately, they are part of the regulator. Replace the regulator and the new one comes with new brushes. :)

You can get a very good regulator at the Fastlane on this site for about $14. As long as the alternator isn't noisy and the grooves are not real deep in the rotor, then go for it. If for some reason this doesn't get the job done, pull it out and put it in your toolbox for future use. How can you go wrong for $14.

Hope this helps,

feel like a duffus
 

my alter ego mickey le dunce' visited yesterday. he noticed almost immediately that the belt tension was way off. very loose. tightened the adjuster. and proper voltage. did notice that i am missing the nut on the adjuster bolt at rear of alternator. will stop by hardware store and get nut and washer. and tighten. thanks to all. and hopefully i will be smart enough to check belt tension in the future. in fact did check tension on my other 123 - also 83 but a 240d with a clutch - and found the adjuster nut missing and belt slightly loose. thank you again.