Rattling sound from alternator? - PeachParts Mercedes-Benz Forum

HuskyMan · #1 05-11-2016, 01:03 PM

OK, with the new battery the car starts right up. However, there is a rattling sound on/near the alternator. At first, I thought it might be the air cleaner mounts so I checked those and they look fine. I did buy some lock nuts to use on the back sides of the air cleaner mounts and tightened them down to further squelch any movement/rattling.

I tried throwing a glass of water on the belts with the engine running. The rattling sound momentarily stopped. One mechanic thinks that the problem might be bent fan blades on the alternator. How can I tell if the alternator fan blades are bent? He mentions using a large flat head screwdriver to move them back to original position.

quote from mechanic's web site:

"I have a 1981 300D. A few weeks ago the charge indicator light came on, so I replaced the voltage regulator (thanks for the plastic tie), and the light went off. Two weeks later I was driving with the windows down, and heard an unfamiliar metallic noise coming from the engine. The sound is coming from the front - near the alternator and water pump area. Per your advice I poured water over the belts and...the noise stopped. I sighed in relief, until I noticed that the belt had slipped on the alternator, which had stopped spinning. When the belt caught again, and the alternator started to spin, the noise returned - it's a grinding sound. This sounds like I need a new alternator, but I'm hoping that's not the case. Any ideas on what else I could do to try and isolate the noise further? If I do need a new alternator, is that something a novice could install? Thanks!

i Michael, first check to make sure the metal fan blades behind the pulley are not rubbing against the alternator body. They sometimes get bent and rub. You can pry them back out with a flat blade screwdriver. If that does not help you will need to remove the belt and spin the alternator by hand to see what is going on."

leathermang · #2 05-11-2016, 01:12 PM

Do you have an idler pulley ?
That needs to be checked also... just had this problem with my F150.

HuskyMan · #3 05-11-2016, 01:37 PM

Does a 1984 300DT have an idler pulley? Quote from the Haynes manual for the 300D.

"For each component there will be an adjusting bolt and a pivot bolt. Both bolts must be loosened slightly to enable you to move the component. Hold the accessory in position and check the belt tension. If it is correct, tighten the two bolts until just snug, then recheck the tension. If the tension is all right, tighten the bolts.

It will often be necessary to use some sort of pry bar to move the accessory while the belt is adjusted. If this must be done to gain the proper leverage, be very careful not to damage the component being moved or the part being pried against."

vstech · #4 05-11-2016, 01:49 PM

if you remove the turbo/air filter u tube, you should be able to see the alternator fan spinning... if it's bent, you should see it with a good light.

Diesel911 · #5 05-11-2016, 01:53 PM

On the surface it sounds like the Alternator and or Water Pump Bearings may be no good. Use a piece of broomstick, long screwdriver or mechanics stethoscope placed on the part you want to listen to determine where the sound is really coming from.

I have a mechanics stethoscope but prefer to use a 3-4 foot broom stick with one end on the part and the other end on my Ear. The broom stick keeps you way away from the moving parts and the stethoscope sometimes requires you to get your face closer to things the I would like.
Also if the stethoscope gets caught in some moving part it is stuck in your ears making it more likely your face is going to be pulled towards the moving part.

Lastly I find the stethoscope to be irritatingly loud.

HuskyMan · #6 05-11-2016, 03:51 PM

I removed the tube from the air cleaner then started the engine. It doesn't seem like the alternator fan is hitting the alternator. It sounds more like the bearings have gone bad. Do any of these car parts place have a way to check to see if it is the alternator bearings? If it is the bearings, is there anyway to replace them?

leathermang · #7 05-11-2016, 04:51 PM

Quote:

Originally Posted by HuskyMan

I removed the tube from the air cleaner then started the engine. It doesn't seem like the alternator fan is hitting the alternator. It sounds more like the bearings have bone bad. Do any of these car parts place have a way to check to see if it is the alternator bearings? If it is the bearings, is there anyway to replace them?

Yes, the bearings can be replaced. Look around your area for a small town in a agricultural area... a generator/alternator/starter shop in an area like that will typically be able to completely refurbish YOUR actual alternator.
If you can not find any where you are... pm me.... I have a good one 20 miles north of me...

HuskyMan · #8 05-11-2016, 04:52 PM

OK, I'll check around and see what I can find. Is it possible to DIY R&R of alternator bearings? Are there two bearings (front and back) or is there only one set of bearings? Any youtube videos for us DIYers?

Diesel911 · #9 05-11-2016, 09:40 PM

There should be 2 threads on changing the alternator bearings.

Be sure to scribe a line acrossed the Alternator Housing and related parts so they go back in the same position.

Repair Links
Fast navigation Fast navigation Do It Yourself Links

Diesel911 · #10 05-11-2016, 10:14 PM

Not sure this is what you need as I cannot view it. It has it is for an 88 Volvo.

https://www.youtube.com/watch?v=6o_OrF2S_UA

HuskyMan · #11 05-12-2016, 10:09 AM

I know that some of the car parts place, O'reilly, Advance Auto, Autozone and Napa can test the charging system of a car. Is their method of testing the charging system (i.e. alternator) accurate?

KarTek · #12 05-12-2016, 10:15 AM

Does the alternator pulley have an overrun clutch? I heard these going bad and it makes the alternator sound like it has rocks rolling around inside.

HuskyMan · #13 05-12-2016, 10:24 AM

Quote:

Originally Posted by KarTek

Does the alternator pulley have an overrun clutch? I heard these going bad and it makes the alternator sound like it has rocks rolling around inside.

I dunno. However, mine sounds similar to what you describe. It is NOISY! Later on today, I'm going to try the broom stick method to see if I can hear it better.

BillGrissom · #14 05-12-2016, 02:51 PM

No AOD pulley on a OM617 alternator pulley (I do have on my 2002 T&C). First verify that the alternator fan blades aren't striking the bracket which is just below the blades. It was on mine, just slightly, after a belt replacement. There is very little gap, but maybe my bracket was bent. Regardless, I wacked it down a bit to "fix 'er".

If you have never adjusted or removed the alternator, have fun, and plenty of different wrenches on hand since they barely fit around all the stuff like EGR valve and AC tube. I re-designed so those two parts are no longer in my way, plus frame-mounted air cleaners on both my 300D's, so now I can loosen the alternator in a few minutes, but still not as quick as on my 1960's cars (30 sec).