Two days ago, the 1984 300D let go with a squeal that sounded like an air siren going off. The car would still start and had good oil pressure. So...I popped the hood and noticed the drive belts were smoking AND hot!!! So.....decided to call for a tow truck and had her towed home.

I've known the alternator bearings were going bad for some time so I ordered a new 65 amp alternator which should arrive Monday. I also ordered new Contitech drive belts. I'm about to remove the alternator and check the bearings/turn the shaft to make sure that is the problem. Anything else I should check????

Check the bearings in the idler pulley. I've had mine fail twice. Once was the oem and then, being new to W123's at the time, I replaced it with either a URO or Meyle and that one failed within a year. Oem from MB was about $37 (if memory serves??).

Good luck.

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Baton Rouge, LA
1977 300D Non-Turbo

Water pump.
I replaced mine on w210 om606 yesterday.
All week cold starts equal belt squeal for at least two to three minutes until it settles down- alternator only putting just over 12v out until noise stops and then back to the usual 14v.
No play in water pump shaft when removed but spin it and its kinda rough, popped in a plastic bag and put in the fridge for a while until cold and then it would hardly turn and groaned loudly.
Low voltage result pointed to alternator but appearances are deceiving.

That's a great tip for the future! I've never thought of putting it in the fridge.

Thanks.

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Baton Rouge, LA
1977 300D Non-Turbo

Yes only went tight when cold , then as engine warmed it would free up a bit.
It must have had a fair amount of drag though as engine feels much easier to rev with new pump.
During the squealing turning off ac and all electrical loads made no difference.

Yeah, that was a good diagnostic catch by you! Thanks for sharing.

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Baton Rouge, LA
1977 300D Non-Turbo