bearing vs. belt noise

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  #1  
Old 07-30-08, 05:12 AM
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bearing vs. belt noise

I have a 2002 chevy venture that has a squeal in it when you rev the engine. When idling everything sounds fine, when driving at about 15 mph you start to hear a squeal that is not real loud but kind of annoying. I'll probably look into it tonight but what is the best way to find out if it is a bearing somewhere or a belt causing this. Is there a difference in the sound for each? If it was a bearing on one of the components would it be there even at idle?
 
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Old 07-30-08, 12:24 PM
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Belt and pulley noises can be tough to nail down sometimes. The most likely candidates for bearing noise are the tensioner and idler pulley bearings. Very common for one or the other to fail and then take out the serpentine. If the belt has plenty of miles on it, good idea to change it out as good preventive maintenance. While the belt is off you can spin the idler and tensioner pulleys and listen for dry bearings. You can also move the pulley side-to-side and in-and-out to see if it has any excess play in it. On my wrecker (350 Chevy engine) I change the idler and tensioner pulleys whenever I change the belt; they're not that expensive and it's a major inconvenience when one of them lets go.
 
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Old 07-30-08, 12:33 PM
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Tow guy is def the expert.

From a driveway mechanic..get a stethescope at the auto parts place. Carefully, (carefully carefully!!) put it on the mount or mounting bolt of what might be making the noise...have someone rev the engine and if you hear the sound from what yer touching increase, well, there ya go.

I got one of the cheapo ones, and I can't tell you how many times I've used it for all sorts of things. Pipes, gas grill, PC, table saw, etc, etc. Can't beat it for trying to isolate noises.

Be advised though, the sound you hear thru the air, can be very different from the sound using the stethescope.
 
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Old 07-30-08, 01:03 PM
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it is hard to explain verbally. i had no trouble ever to distiguish between the 2. bearing noise has metal base to it. sort of cruntcheniss.
belts make noises when they slip, so it's more of a slipping/rubbing noise. sort of high pitch/chalk on the board. peculiar thing about belt noise is that it mostly happens when engine is under strain. taking off, going uphill, taking sharp turns, sudden acceleration. if your noise is present in P(parking) or N(neutral), and is simply relevant to rpms - there's no strain on the engine, so i'd bet on bearings.
also, you can exemine belts and if they go real shiny on the inside, where they move on pullies - probabaly it's slipping.
now, all this is ok for any car i owned or worked on, except mitsubishi eclipse. but that's a different animal.
virtually any car i know has the 1st bearing engine noise coming from alternator bearings.
if you have harbour freight tools around, they sell mech's stetoscopes for a couple bucks. or you can use dry stick, place one end against the part in question, place thumb firmly on the opposite end, and place your ear against the thumb. very good stetoscope.
 
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Old 07-30-08, 04:46 PM
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It used to be so easy in the old days !! We had enough room to safely run a bar of hand-soap, or chalk on the underside of the belt (which comes in contact with the pulleys) and if it was a belt, the noise was gone. Few days later if it started again, give it another coat to get you through. Anyway, If your not sure, and belt is due for change anyway, spray a little WD-40, On whatever surface touches the pulleys, both sides if necessary, but wear eye protection. I find a spot that I can SAFELY !!, spray with car idling, from the side, and mist both top & bottom because of the fact that my serpentine belt goes around pulleys, but the back side (smooth) also rides on idler pulleys. A quick mist, and noise disappears, telling me it's 99.9% likely that it's the belt making the noise. Changed the belt, noise gone.
 
  #6  
Old 07-31-08, 04:18 AM
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Thanks for the info, I looked at the serpentine belt last night and it looks pretty good, mabe a little shiny on the non-ribbed side. THis belt was changed about 8000 miles ago. Anyways I'll investigate the pulleys and tensioner now as it is a fairly loud high pitched squeal when you step on the gas in Nuetral or park.
 
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Old 07-31-08, 04:48 AM
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I don't think any of us mentioned it, but does having the ac on/off make any difference?
 
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Old 07-31-08, 04:53 AM
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Does it with the ac on or off.
 
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