My ML have this odd pitch sound which I can pin point to the alternator. I removed the serpentine belt and checked all the pulleys, the pulley on the alternator has no play and spins quite freely. All other pulleys are fine and have no play.

If the alternator bearing goes bad, what would be the symptoms? I would think the pulley won't spin as freely as it should but I don't know for sure.

Any thoughts?

p.s.: the truck has 100k on it with the original alternator. I have replaced water pump and belt tensioner 40k miles ago.

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98 ML320 (gone but not forgotten)

1.http://www.wai-wetherill.com/products/partimage.cfm?wai_num=10-3043-4W
2.http://www.wai-wetherill.com/products/partimage.cfm?wai_num=6-203-4W

WAI is a seller to wholesale accounts ONLY,Your electrical reman shop can order the bearings for you.
OR you can order them from the Mercedes dealer (At a premium price).

WAI's offerings for your Bosch Alternator:
http://www.wai-wetherill.com/products/sresult1bom.cfm?ManufName=BOSCH&item=0-123-510-079#0-123-510-07901

THIS IS an incredible DIY (Illustrated) by BA over on V12 Uber Alles:
http://v12uberalles.com/Alternator_Bearing.htm

(Almost all Bosch alternators are similar,and you can use his instructions on
yours!)
[Do Not,Do Not GRAB the Alternator Pulley (WHILST YOU USE a Air or Electric
ratchet to remove the nut) with PLIERS,Vise Grips ,Etc. OR you'll be buying a
new Pulley!] Ask me how I know! 'Cheap rubber "Strap" wrench from HF is the
way to go.

Attached Thumbnails

       

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'84 300SD sold
124.128

Thanks man. The rebuild DIY page is incredible. I found a similar page from a range rover owner but it didn't have that many pictures. I ordered the bearings from a MB dealer online, the bearings were not too expensive, the large one is $38 and the small one is $16. The most expensive part is the voltage regulator. Anyhow, thanks again.

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98 ML320 (gone but not forgotten)