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Discussion Starter #1
I notice this odd noise when the engine is idling, and I measured that it oscillates 7 times per 5 seconds. My idle is around 700 to 650rpm. I'm suspecting the fan clutch, since when I got into an accident I noticed the fan isn't straight anymore and the outer edges of the blades travel forward and backward when they rotate. Could I be correct in this?

The sound is a hollow, metallic oscillating sound at idle. I couldn't hear it at other engine speeds perhaps because of the engine noise. I checked the water pump bleed tube and it's not leaking, so am I correct to assume the water pump is still intact? (even after the accident where the radiator pressed on the fan?)

Further observation noted: One cycle would produce a pair of noises, like one after the other, and each pair would repeat 7 times in 5 seconds.

I pressed on the air cleaner housing to prevent rattle, even pulled it up to check, but it was not the air cleaner. The sound was still there. The only thing I could think of is the fan or fan clutch area.

If it's the fan clutch, then I might as well have the belts changed...

Any tip or advise is appreciated!
 

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1991 300 SE
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18,534 Posts
The fan-bearing bracket may be coming apart. You’d need a new pulley, bearing bracket, O-ring, and belt. Is the fan blade hitting the pulley?
 

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Discussion Starter #3
Jdc, I think the bracket is the one where the four bolts screw on? Where the fan clutch also screws on? I haven't checked if the blades get in touch with the belts, but so far I haven't noticed. Where do I find this pulley? I haven't seen any online. Junkyard part? When I do get a new fan clutch I might as well upgrade my fan to the 9 bladed one. Thanks again.
 

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Discussion Starter #4
Update:

I could easily move the fan when engine is not running. Tightened bolts and still could move the fan. This is a guarantee that fan clutch needs to be replaced, right?

Now for the pulley. It seems the pulley is balanced, no wiggling when idling/spinning. It seems that only the fan is wiggling like a figure-8 when seen from above the engine.

So, do I still need the pulley? Or will a new fan clutch and blade work? Mercedessource has one for $85 used:

http://www.mercedessource.com/store/item.php?item=MERCEDES%20300D%20300SD%20TURBO%20ENGINE%20FAN%20UPGRADE%20123USED-EFU

What do you think? Yes, I know the belts need to be replaced as well. Will getting a used fan clutch be good? Or am I better off with a new one? ($100+ at most stores) plus the new 9 bladed fan ($65 cheapest I found).

Thanks again.
 

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1991 300 SE
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If the blades are hitting the pulley or belt then it could be the assembly. If not then the clutch me be bad, but he sound you described is more like the assembly.
 

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Discussion Starter #6
Umm, what assembly? I got lost there. You mean the whole fan-clutch-bracket-pulley?

No, the blades don't hit the pulley nor the belt.
 

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'81 300TD Turbo
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416 Posts
Hey karugs, the fan should turn by hand. It should have some resistance, but should turn fairly easily. If it spins freely or if it is very difficult to move, change the clutch.

As a matter of fact, you can hold a clutched fan still with an engine at idle (it's a relative movement thing), although I wouldn't recommend this practice unless you are shooting for a Darwin Award. [xx(]
 

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Discussion Starter #10
Thanks for the tip. The fan clutch seems to be intact as per the mechanic's advise. It does rotate but has moderate resistance. But...he pointed out two possible areas of noises.

Alternator - bearing
Turbo fan - bearing

Now I'm stumped, could it be an alternator bearing, or a turbo fan bearing? I'm pretty sure the alternator was not hit when I got into an accident since the impact is on the left side while the alternator is on the right side. Checked the pulley and has no signs of scrapes from the fan shroud.

Now for the turbo bearing, could it be possible? Here's what I did. I retightened the J shaped tube linking the air cleaner to the turbo inlet and the sound was slightly muffled. But when I loosen it, the sound is different (like air is being sucked in, not the rattling). Also, now that I've tightened the J shaped tube, the sound seems to come and go at various times. I can hear it strongly when accelerating now, like a large gust of wind blows through your ears. It's like that, accompanied by the rattling sound.

I will open up the J tube and see for myself if the fan blades are OK. Just to confirm, the electronics are all working great, I feel no weakness in power, although that sound really bugs me. It can even be felt on the accelerator pedal, like it's vibrating and you feel a metallic grinding feeling to it.

To isolate the noise we lifted the air cleaner and the noise was still there, so the rattling is not the air cleaner. To make sure I will remove the cleaner tomorrow and run it, see if I still have that sound. I'll remove it once hot, since we all know the sound of a cold diesel engine idling is different.

So now my question is, could it be possible that either the alternator or turbo fan bearing is at fault? Geez, this is some major work right?...[xx(]
 

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'81 300TD Turbo
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Do yourself a favor and do one of two things:

1. Go out to Sears or wherever and get yourself a mechanic's stethoscope.

2. Make one out of some tubing.

The first choice is the best, as it will be purpose made and much easier to work with, but the tubing will work in a pinch.

A stethoscope is an invaluable tool and they don't cost much. I can't count the number of times I've used mine to find the source of a noise. Even if you don't find the noise with it, it can help you to quickly rule out suspected sources.
 

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'81 300TD Turbo
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BTW, wouldn't be so sure about the turbo. Yes, the bearings could be going, but I don't think you'd hear a rattle.

There isn't much clearance between the turbo's impeller and turbine vanes and the housing, so if things were bad enough to cause a rattle I'm guessing it should have shelled out before now.
 

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1991 300 SE
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I don’t think it’s the turbo, either. For the bearings to be that bad the seal would be as bad and in that case there’d be more smoke and high oil consumption.
 

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Discussion Starter #14
I did use my long screwdriver as my stethoscope, and it seems the turbo is out of the question. But now I'm worried about the alternator, could it be the bearing? There was alot more vibration on the alternator and it sounded like it came from there. The mechanic told me to remove the belts to see if it's the alternator that's causing it (if noise is gone, it's the alternator). I have yet to look on articles on replacing belts to do this.

By the way I removed the air cleaner and ran the engine with and without the J shaped tube. The noise is still there. I could now hear it when driving the car, it sounds like when there's a V8 engine revving up beside you. That's how it sounds from inside, or could it be just my engine? I swear I never heard this before. I'll see if it's just me who's adjusting to the sound.

Also a neighbor helped me, and he also thinks it's the alternator.

Now my question is, how long do I have? The mechanic said it could lock up at any time if it's indeed the alternator bearings that's going bad. Lock up = disaster [xx(]

By the way off topic: when I removed the breather hose going from the valve cover to the air intake, I forgot to put it back in. When I started the car I noticed there was "steam" going out of it. Normal? Blowby? Checked for oil droplets, nothing on my hand when I placed it above the hole (when the car has just been shut off). Should I have tried it while it was running?
 

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Discussion Starter #15
Ok I got the stethoscope and poked around. Now it seems more clear, the alternator gives out a loud, rattling sound audible when you let the "steth" probe contact the alternator.

Am I correct in using the stethoscope: poke and hold firmly onto the surface?

Now, another question [:D]: Does anybody have a remanufactured working alternator lying around?

Question regarding online purchase: Do I need to remove the voltage regulator if I buy a remanufactured one online? What is the "core" when you buy one online?

Thanks again! Best $10 I've spent on the stethoscope.
 

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Discussion Starter #16
So it IS the alternator. Went to local mechanic, removed alternator belts, started the car. NO NOISE! Installed alternator belts again, and started car. NOISE IS BACK!

Now where was that good online store again? ...

I hope to hell this is the last repair I need to do! [}:)] Mechanic said $100 for installing alternator and the store was asking $130 for remanufactured alternator. $40 core. Good?? Or better to DIY?

While I await replies I'll go ahead and order an alternator.
 

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I've never changed one yet on a Benz, but have changed quite a few others. Only one of these was a real chore... a Dodge Omni. If you can get through changing an Omni alternator, nothing in the world will ever scare you!
 

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Discussion Starter #18
Quick, help!

OK I just got home from school. Checked my belts, and one is OUT of the pulley. I noticed metal pieces (like filings), so I checked the alternator and the fan has been scraped somehow (by the belt I think). The alternator pulley is loose as is the alternator fan. Both belts are intact (no snapping) but one is just out of the pulley system. The one still on the system is loose. Thank God for German engineers who added that second belt!!

Now my question: Do I just reinstall the belt and then tighten the tensioner? I know that I should loosen the 3 rear bolts (17mm) first before tightening the tensioner. Tighten the tensioner by turning CW right? Loosen for CCW? Won't that put alot of stress on the now loose pulley and fan??

I hope to God the package (alternator + belts) arrives today. My mechanic can do the job tomorrow, luckily, so if it arrives today it'll all be done tomorrow. If not I'll have to bring my mom to work and rush to school at 8:30am

As I await your replies I'll be online, waiting for the package, letting the car cool down so I could hopefully do it by the time I receive advise from you guys. THANKS!
 

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1982 300sd turbo
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if your still running on the noisy alt. take belt that slips off, off,cut it, wonder why mb never put on a volt meter? will be good after new alt. and belts arrive i bet. [:D] n0rt
 

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Discussion Starter #20
Nort, thanks. But I just got back from retightening it. [:D] It's good experience though!! Had to redo it since it loosened up the first time. Another skill I can add to my list [:p]

THANKS TO BOOSTNBENZ!!!

Also, the other belts need replacing (P/S and A/C) so I had to reinstall this loose belt just in case anything happens. Then at least I'll have peace of mind driving the car to the mechanic hopefully by tomorrow.

Seems that this is what happens. The alternator fan is loose (I can move it even with the belt tight on the pulley system) and it's banging on either the alternator body itself, the tensioner bolt (part of it), or the alternator bracket. Either way I'm not running it tomorrow until the belts and new alternator arrive. By then I hope the belts are still tight (by my own DIY) and I can give it a final drive to the shop where the mechanic will replace the alternator and belts for $50.

Once again, I'm crossing my fingers and hoping for the best. Will keep you updated if anything ...
 
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