MB Repair

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

Hard to tell without looking at it. One problem could be that the pulleys are not in proper alignment. That could draw the blades back .1 of an inch but why it is intermittent is a puzzle.

The rear bearing may be the real problem but you should be able to feel the in and out play. Let us know what you find. [img]/forums/images/icons/confused.gif[/img]

Carl,,,

Check the adjustment bracket for the alternator thats located just below the pulley/air vane. I suspect you'll find that the vanes are contacting this bracket, and that's where your metal dust is coming from. It is common for the bracket to get bent and rub on the air vanes. Often times, it will only rub after heat has expanded everything. The bracket gets bent if you try to adjust/remove the alternator without first loosening the locking bolt.

HTH,
Dave

Tenebrous & Karmakanic

Thanks for the tips - the re-man alternator came last Friday and I installed it. The mounting is two 14mm bolts to the engine so no adjustment bracket since it is a serpentine belt with tensioner. Takes about 20 min to RR.

The cause of the problem was a loose pulley [img]/forums/images/icons/frown.gif[/img]. I was able to turn the pulley off by hand. The fan is a press fit setup then held down by a large thrust washer after which the pulley goes on then the 22mm nut. I had checked this out before and it seemed fine, and as stated by karmakanic when warm it expanded enough to cause the vanes to rub the casing.

The alt shaft has a 8mm allen in the end that needs to be held while tightening the recessed 22mm nut. Must be a special tool to do this but I used a 22mm socket (wrapped with rubber) with the 8mm allen through the socket then used a pair of vise grips on the socket edge.

So at the end of the day, have a new (and spare) water pump, and new (and spare) alternator for $225, and peace of mind for the next 100K+ miles.

By the way the best source I have found is a place in NC Alternator & Starter Express for all makes and models of cars trucks etc. Very reasonable - the local auto parts store wanted $210 plus my core. Their price $75 incl. shipping and no core return!!

Carl

I am glad that you found the problem. Sometimes those things will drive nuts.