Have had a fun time lately with my 300D MB. Was coming home last week when I heard this noise sounded like I was dragging a stick..

The noise would go up/down with engine speed so drove the remaining two miles then pulling in the drive the noise stopped.

So I suspected the water pump brgs since there was evidence of some bearing dust/rust from the outside bearing and play in the shaft with the belt off. So ordered and installed a new water pump last Sat. Tested and drove for an hour - problem solved. [img]/forums/images/icons/smile.gif[/img]

Then earlier this week took it out and noise started again, then stopped when I pulled off the road to check it out - it stopped making the noise. [img]/forums/images/icons/confused.gif[/img]

Going home no noise at all.. Seemed like when the engine go up to temp the problem would start then disappear again as fast. Thought it could be the fan clutch too but that checked out fine when I did the pump.

Further investigation of the alternator I saw some evidence of rubbing on the face so pulled the belt off, checked the bearings and end play - none present. I did bend some of the vanes for about .100" clearance from the face of the alternator.

Thinking this was solved took it out yesterday for a trip, and it started again after about 3 miles, pulled off the road and sure enough it was rubbing the face and I could see metal shavings. Drove home (making no noise) pulled the belt off still no play in the bearings.

I had discounted the alternator as I had it rebuilt 20K miles ago, and have no charging problems etc. but now I have ordered a reman unit and expect it in next week.

So, the question is, what would cause the alternator vanes to move .100" or more when there is no apparent problem in the bearings?

I intend to do an autopsy once I get a new unit, but thought some of you might have some idea how this could happen.

Carl