Knocking/rattling from alternator housing, new alt didnt help

tmblackflag · 06-17-2012, 06:33 PM

I have a rattling/knocking sound at idle coming from the alternator housing. If i take a stethoscope to the housing I can hear the rattle pretty good around the middle of the black shroud that the housing bolts into. As i move closer to the top of the shroud where it meets the housing it gets louder.

I had suspected the alternator bearing were going bad and put in a reman bosch alternator. Now the sond hasn't gone away. It might even be a bit louder.

I've got 6 shims on the fan pulley and tension looks good with 2 inside, 4 outside. Could the air duct that bolts onto the back of the alternator be making the noise?

gsxrken · gsxrken's Garage

Can you post a youtube video? I can't see the air duct making noise. Have you taken the fan belts off and run the car briefly to see if it goes away?

tmblackflag · 06-17-2012, 08:39 PM

Will try disconnecting the fan as well as posting a video tomorrow. Thanks

Driver_X · Driver_X's Garage

If the noise is gone with the belt disconnected, I would suspect a cracked fan housing...

tmblackflag · 06-18-2012, 06:55 PM

Just got home from work and took 3 videos

1st is just checking fan belt tension. Is this about right? 20120618_185902.mp4 - YouTube

2nd gets you a nice listen in on the rattling/knocking sound with the fan belt attached 20120618 190004 - YouTube

3rd is with the fan belt disconnected. Sound is lower but i can definitely still hear the rattle. 20120618 192112 - YouTube

A little more background on the knocking sound. When i took the alternator out over the weekend I found a decent sized crack in the alternator housing. I had it welded up by what i believe to be a competent magnesium welder. You can see pictures of the before cracks here. Unfortunately i didnt take an after picture before i out it back in.

went to replace alternator and housing is cracked

monkeyodeath · 06-13-2019, 03:05 PM

Sorry to resurrect an old thread, but did you ever figure out what this sound is? My car is making the exact same noise.

I noticed a little play in the fan pushing it forward (toward the front of the car). I'm also seeing some small cracks in the fan housing.

nathanbs · nathanbs's Garage

I had this noise recently from a worn woodruff key on the alternator/fan. New key solves the problem

monkeyodeath · 06-13-2019, 09:43 PM

Quote:

Originally Posted by nathanbs

I had this noise recently from a worn woodruff key on the alternator/fan. New key solves the problem

Ok, cool, I'll check and see if that's an issue.

Sounds like it's time for me to park the car for a little bit and pull the fan stuff off to see what's going on, as well as get the fan shroud re-welded.

Tyson Schmidt · 06-13-2019, 10:52 PM

Check that the fan isn’t rubbing the housing.
The housings warp and crack and allow the fan to touch. It will make an awful noise

monkeyodeath · 07-31-2019, 07:04 PM

Just an update to my situation -- pulled the fan apart and found that I had a very cracked housing. Sent it to mb911, who welded it up nicely.

Just got everything back together and at least for now, the rattling sound is gone.

I rebuilt my alternator at the same time and found that the bearings were still in good shape, so I don't think that was part of the problem.

RedCoupe · 07-31-2019, 07:35 PM

Quote:

Originally Posted by monkeyodeath

Just an update to my situation -- pulled the fan apart and found that I had a very cracked housing. Sent it to mb911, who welded it up nicely.

Just got everything back together and at least for now, the rattling sound is gone.

I rebuilt my alternator at the same time and found that the bearings were still in good shape, so I don't think that was part of the problem.

Thanks for the update. Nice to know the cause of the noise.