What's that squealing noise?

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Mercedes W123

The W123 chassis covers 240D's, 300D's, 300TD's, 280E's, and several other models of Mercedes coupes, sedans and wagons from model years 1977 to 1985.

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joshuaahopkins @joshuaahopkins

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Posted: Jan 27, 2018

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What's that squealing noise?

I have a 300D that makes a squealing noise, similar to a drive accessory belt. I replaced all 3 belts with high quality ones with no change. I later noticed the noise was much worse when I was using electrical systems with large draws (headlights, heat, A/C). I replaced the alternator and it seemed to do the trick for about a week, then it started again. It doesn't make the noise until it's above an idle speed, and when it does, it's impossible to diagnose where it's actually coming from just from the sheer volume. Has anyone here experienced the same issue (and figured it out)? Thank you in advance.

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mayer @mayer

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Posted: Jan 27, 2018

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Sounds like you may have a pulley wheel trying to lock up or bearing failing.

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oldturkey03 @oldturkey03 Rep: 782.1k 1.1k 893 2.3k · Answer 1 · 2018-01-27T12:34:18-07:00

joshuaahopkins that is one of those where you could be chasing the rabbit down the rabbit hole. Let's make the assumption that this is not caused by your alternator. You do want to make sure you have the right belts and that the belts are not riding to high. Adjust the belt tension properly. Let us know if the squealing is different if you turn the AC on/off. Check all the pulleys since I seem to remember that they do not have a Woodruff key holding them on the shafts. Check all those pulley bolts. Remove your belts separately to see if that changes the noise. I do believe it has separate belts for power steering, AC and alternator which should at least get you a bit closer to where the noise originates from. and check the bearing by moving things by hand. Use a mechanic stethoscope to see if you hear any grinding etc. See if you can feel any grinding or have some wobble when you move those. The squealing on my 1982 240D was caused by a bad water pump bearing.