low 'friction sounding' hum and burnt smell... alternator problem?

[mvmcali]

my 2001 QX4 has 130k miles.
normally engine idles quietly with very little vibration/noise

the last week or two, i sometimes start it and hear/feel a low pitch noise (hum) coming from engine compartment. i describe it like a 'friction or rubbing type sound. i can usually smell a slight 'burnt rubber smell' when this happens. to describe the sound i'd say like a belt not running smoothy over a pulley).

local garage thinks my alternator/alternator pulley is going bad and its $500 replacement. I feel like they are guessing a little bit as opposed to actually trouble shooting it and narrowing it down to this particular problem. I dont seem to have any problems with the charging of the battery which is about 4 years old now and 'passed' the shops battery test with 12.44V 'risk-moderate'.

does this problem sound like a dying alternator?
thx!

[atraudes]

If you have a long screwdriver or metal rod, you can put one end on the alternator body while the engine is running and put your ear up to the other end. It'll act as a stethoscope and you'll be able to hear it as though you had your ear pressed up against it. If it is the alternator, it'll be much louder than anything else under the hood. You can also probe other components like the A/C compressor to pinpoint it and compare noise levels.

My guess is the alternator as well, but have a listen for yourself. When my wife's alternator bearings gave out it made a loud whining noise similar to an old ambulance siren. Other than the noise it functioned fine, though I didn't have it tested to see how well it was functioning.

[Buzzman]

Sounds like the alternator is dying.
Mine started acting the same way, and I ignored it. Wrong move.
It crapped out after about a month of making noise, and left me stranded with a dead battery.
You can get a rebuilt alternator for less than the $500 quote. I suspect the quote includes labour, so it's not totally out of line.
It is a major PITA to replace by the way.
I was going to do it myself, but decided against it after taking a look. Smart move on my part.
I paid a flat rate, and the tech that did it was cursing the whole way.
It has to be replaced/installed from underneath. You can't get it out the top.

[mvmcali]

If you have a long screwdriver or metal rod, you can put one end on the alternator body while the engine is running and put your ear up to the other end. It'll act as a stethoscope and you'll be able to hear it as though you had your ear pressed up against it. If it is the alternator, it'll be much louder than anything else under the hood. You can also probe other components like the A/C compressor to pinpoint it and compare noise levels.

My guess is the alternator as well, but have a listen for yourself. When my wife's alternator bearings gave out it made a loud whining noise similar to an old ambulance siren. Other than the noise it functioned fine, though I didn't have it tested to see how well it was functioning.

thanks guys for quick response. i will try the poor man's stethescope idea. i was actually surprised that 'wheel works' told me that some mechanics use a stethescope to isolate the vibration but apparently they don't do it. kinda makes them sound like amateurs

im guessing from the various posts I read that changing this thing is very difficult mainly because its hard to get to...

[atraudes]

Correct, lifting the engine a bit may be necessary to get it out, though it should be possible to do without. I've heard from some folks that it wasn't a huge deal, and I've heard from other folks that they'd sooner saw off their leg than do it again...I'd say read a few posts for yourself and make your own call. Personally when it comes time to do mine, I'm planning on letting a shop do it.

[yeldogt]

The clutch for the AC compressor is another possible source.

The alternator can hum because of a failing bearing but also they can produce an electrical hum -- does the tone/ sound change when various electrical items are turned on? Normally heard just off of idle.

The alternator is a pain to remove -- get a quality replacement for that reason. I was able to get a very good price from a dealer in the midwest -- The alternator is made by Hitachi -- you want a true hitachi rebuilt. Most are rebuilt by others or made in china copies.

Removing the belt and spinning the pulley should show a failing bearing -- The rubber smell is strange. For the belt to be slipping and creating that much heat -- I can't see how the alternator would survive very long. When the clutch in the AC is going -- they smell.

Get someone who knows what they are doing --- this should not be something very hard to figure out. Be careful .. working around a running engine trying to hear a sound with a screwdriver is dangerous.

[mvmcali]

thanks all. it turns out it was the alternator that was going bad due to bad bearing.
i did actually use the screw driver trick myself to confirm that the vibration/friction sound was originating on alternator. I agree with yeldogt that you have to be real careful sticking a long screwdriver into that engine compartment!!
-I was wrong to describe the smell as burning rubber. it was more like burnt tran fluid (which makes me think the bearings in the alt were getting real hot
-i had a reputable garage do the replacement $325 for part + $132 labor = $457 , they told me they used a high quality denso (or delco?) remanufactured part.
-the part cost sounded a bit high but some other garage told me that when 'they' buy a part, they pay more than you or I do because the part cost to them will cover their labor if they have to replace the part for you during the warranty period. does this sound legit to anyone?
-I trust the shop I went to as they have a good rep and have done some repairs for me before... BTW one reason i like them is a couple years back my car seemed to be leaking diff oil and another garage wanted to take apart my front end to replace a bad seal somewhere in the front drive train. the 'good' shop realized that it was simple oil leak from oil cooler which dripped down onto other parts, repair cost was only $130 instead of god knows what!

[Buzzman]

thanks all. it turns out it was the alternator that was going bad due to bad bearing.

-i had a reputable garage do the replacement $325 for part + $132 labor = $457 , they told me they used a high quality denso (or delco?) remanufactured part.

Not a bad price, but not great either.
I paid about $240.00 (CND) for a re-man alternator, and it came with a one year warranty.
I paid $120.00 for labour.