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Old 09-13-2007, 02:25 PM   #1 (permalink)
BenzWorld Junior Member
 
Date registered: Apr 2005
Vehicle: 94 E320 Coupe
Location: Los Altos Hills, CA
Posts: 15
1994 E320 Coupe Noisy Alternator

The alternator my 1994 E320 Coupe makes a whirring sound and will not go away at any speed. Is this a sign of a major problem about to happen?

Thus far the battery remains fully charged and all electrical systems are working. There is no perceptible dimming of the headlights even at idle speed.

Should I take action to replace the alternator now, or will there be a more definitive warning before it fails altogether.

What's the best course of action. Thanks for insights. advise or comment.
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Old 09-13-2007, 03:25 PM   #2 (permalink)
BenzWorld Extremist
 
Date registered: May 2003
Vehicle: E320 wagon
Location: southern cal.
Posts: 914
Slack the belt and check for play on the pulley / rotor . If the bearings are gone you will hear /feel it . Some of VWs alternators have vibration issues that destroy the alt. havent seen a MB unit do that yet.

Uboater
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Old 09-13-2007, 03:34 PM   #3 (permalink)
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Date registered: Apr 2005
Vehicle: 94 E320 Coupe
Location: Los Altos Hills, CA
Posts: 15
Thanks!
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Old 09-13-2007, 03:40 PM   #4 (permalink)
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Date registered: Mar 2005
Vehicle: '01-E320 & 02-ST2
Location: Adrift on an island...
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Quote:
Originally Posted by MBCoupe
The alternator my 1994 E320 Coupe makes a whirring sound and will not go away at any speed. Is this a sign of a major problem about to happen?

Thus far the battery remains fully charged and all electrical systems are working. There is no perceptible dimming of the headlights even at idle speed.

Should I take action to replace the alternator now, or will there be a more definitive warning before it fails altogether.

What's the best course of action. Thanks for insights. advise or comment.
Hey, MB.

That sound is probably the bearings. If you're good you can just order the brushes and bearings and rebuild it yourself, not too tough at all. Otherwise I would suggest you go ahead and replace it now, you can buy bosch rebuilds with a good warranty on them. If the bearings freeze it will burn up the belt and perhaps strand you.

One other thought, are you 100% sure the noise is coming from the alternator? To confirm you can remove the belt and spin the pulley by hand, or if you have clearance and you're very, very careful, use a long piece of hose (vacuum line is ideal) and insert one end to the edge of your ear canal and hold the other by the alternator, carefully avoiding the belt, fan, etc.

Take care and enjoy the ride,
Greg
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Old 09-13-2007, 03:50 PM   #5 (permalink)
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Date registered: Apr 2005
Vehicle: 94 E320 Coupe
Location: Los Altos Hills, CA
Posts: 15
Thanks for your input Greg.

The brush replacement sounds like brain surgery to me - I think I'll go the rebuild route. I noticed that there is a 90 amp and a 120 amp alternator on the aftermarket. How can I determine which one is the right replacement unit for my car? Do you have a preferred vendor that you use to buy parts?

The Service Tech made a definitive diagnosis that the sound is coming from the alternator and not from the air pump.

Thanks again,
Richard
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Old 09-14-2007, 10:30 AM   #6 (permalink)
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Quote:
Originally Posted by MBCoupe
Thanks for your input Greg.

The brush replacement sounds like brain surgery to me - I think I'll go the rebuild route. I noticed that there is a 90 amp and a 120 amp alternator on the aftermarket. How can I determine which one is the right replacement unit for my car? Do you have a preferred vendor that you use to buy parts?

The Service Tech made a definitive diagnosis that the sound is coming from the alternator and not from the air pump.

Thanks again,
Richard
Hi, Richard.

If you have a second car to use there is actually a local rebuilder not too far from you (Campbell area if I remember correctly), let me find their contact info. You'd take yours down to them, then pick it up, or if they have a rebuild in stock they'll trade you. I was going to use them but ultimately determined mine was just the voltage regulator so I R&R'd the alternator and then R&R'd the regulator. FWIW if your design is like mine (I can't say...) then your brushes are built into the regulator, you pop it off and there they are, absolute piece of cake, but they're not the noisemakers.. To replace the bearings requires disassembling the alternator and removing the pulley, which are much tougher than the brushes but still doable.

I'll PM you the rebuilder info as soon as I have a chance.

Take care and enjoy the ride,
Greg
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