I just replaced my belt on my alternator for my 300D (617 engine) and after a few hours it was loose again. This is the third time this happened. I made sure that all the nuts and bolts were "very" tight. Could it be the pulley? There are three pulleys one on the alternator, Water pump and other on the crankshaft. I'm using a Continental Ribbed Belt 10 x 9.80 original size.


Francis
77' 300D

Place a mark with chalk or other medium to mark the placement of the alternator in its housing when belt is properly adjusted. Drive the car for a few hours and re-check the alternator's location with respect to the mark you made. If the alternator moves, the bolts are not holding it tight.
Good Luck

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William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles

I have seen the alternator moving or a faulty pulley. If the alternator is going bad and siezing at times, it will cause the same thing. This will stretch the belt by overheating.

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM
OWNER OF MB AUTOWERKS .COM

Donnie - what do you mean by going bad and siezing? How do I check if mine has the symtoms you said.


Thanks!

Francis