Alternator bearing noise?

I am getting a humming noise and it is noticeable with engine at idle. The noise appears to emanate from the alternator. Fan clutch is OK. The belts are relatively new and are properly tensioned. However the alternator is original (235k). The alternator itself is charging OK but this does not mean that the bearings are OK. I don't know whether worn brushes make any sound or no so it could also be the brushes. Anyway I'd rather be sure it is the alternator before I yank it. Has anyone else encountered a similar issue like mine?

 

Quite often, the whining like that is caused by the idler pulley of the alternator, making it SEEM like the alternator bearings are going. The pulley is very easy to remove and check, with a failed/failing bearing causing the pulley to be rough to turn manually. Take the pulley off, hold the center between your thumb and forefinger, and spin the pulley. Believe me, you'll be able to FEEL a bearing that's bad, or going bad.

Worth checking, as a pulley/bearing pair, or even just the bearing, are readily available. The bearing is easy to drive out with a socket of the right size, and drive right back in again with a rubber mallet.

Good luck!
Pat☺

 

Second on bench testing the alternator while you have it off the vehicle,

 

Hi Pat,
Hmm ... I am not following what you mean by the idler pulley of the alternator. The alternator belt goes over the fan bracket pulley, the crankshaft pulley and the alternator itself.

 

Just an FYI for around $10 at most auto parts stores you can buy a mechanic's stethoscope and pinpoint almost any noise/whine/bad bearing, just be very careful using the probe around moving parts.

There's a idler pulley and also a tensioner pulley, either could also be your issue and have the bearing going bad.

 

aah ... I see you're talking about. These are the idler & tensioner pulleys that are on the timing belt. They are relatively new on my car. I had replaced them with OEM parts when I replaced the timing belt about 10k miles ago.
I had tried my stethoscope but my problem is I don't have a reference to compare against.

 

At that mileage, brushes are finished. They're usually done at about 200k miles. They're easy to replace. It might be the noise you hear. Either way, if you're going to pull the alternator anyway, do that, remove the brush assembly, and compare it to a picture of a new one. It'll die on you very soon if you leave it in there. And it's a $20 fix.

 

My original alt has 280k miles on it...I have replacement brushes...just been lazy to do it. Part of me wants to see how many miles they'll go.

 

Just be willing to sit by the road or have a jump-start battery with you.

 

I have a 6000Amp jump start

 

AS mentioned above you can buy a stethsescope or use a 2'-3' piece of fuel line to pin point the noise quite easily. Alt brushes and bearings do start to make noise at life's end. No big shakes.

 

Just an update so that the thread can be closed. I replaced the alternator with a rebuilt Denso. The noise went away and all is well now. I still have the old alternator. At some point I'll open it to see whether the brushes were causing the noise or the bearings.