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Old 02-22-2015, 02:52 PM
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Noisy Belt? Please help!

Hello All,

First of all I have a 2001 Jeep Grand Cherokee WJ with the 4.7. About a month ago my alternator went. I replaced the alternator, idler assembly (it had excessive motion at idle and a noisy bearing), and the serpentine belt. Days no slack tanner assembly and dayco belt. Everything seemed great at first, then a strange noise developed after 100 miles or so. The belt seemed to squeal, but only when decelerating. And it only appeared to do it from 1700 RPMs down to around 1000 RPMs. As soon as the engine is either above that or under that the noise stops. And I only notice it on deceleration, not acceleration. This noise is driving me crazy.

I read on here that Goodyear's Gatorbacks are the best belt, so I just replaced the Dayco belt with a Gatorback. The noise seemed better on initial test drive, but now is back and just as loud.

Any suggestions? Could I have gotten a bad tensioner? Any other possible explanations. I have never had a belt noise before and this one is strange that it is only affected at that slight range of RPMS. Not at start up. Not at any other motor speed.

Thanks in advanced for your help!

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Old 02-22-2015, 08:08 PM
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Re: Noisy Belt? Please help!

Did you rotate the pulleys when the belt was off? Also the alternator would be suspect, since the noise started after changing. Does the tensioner work smoothly over its range? Just put a wrench on the tensioner pulley bolt and feel if it has a smooth travel. Last thing to check is if the alternator pulley is lined up with the other pulleys.
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Old 02-22-2015, 10:08 PM
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Re: Noisy Belt? Please help!

The alternator pulley appears to be aligned correctly. When the belt was off I hand spun all of the pulleys. They all rotated freely without wobble. I thoroughly cleaned each pulley when I put the gatorback belt on last weekend. When I put the gatorback on last weekend, the tensioner did have a smooth range of motion. Could it be the alternator? Is there any way of testing this? Would that account for why it makes noise only at that certain engine speed range? Also to clarify the sound- it isn't really a chirp. It is more of a squeal or whine. As the RPMs are falling through that range- I can blip the throttle ever so slightly and it will stop then come back as soon as the RPMS start coming back down. It is only noticed when they are coming down, not during acceleration. Does this help? Let me know what you're thinking and I can do any further diagnosing you advise me to.
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Old 02-23-2015, 06:29 AM
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Re: Noisy Belt? Please help!

When you are standing in front of the engine and play with the accelerator, is there any change to better pinpoint the noise maker? Maybe you have a mechanics stetoscope to help fidning it? I would first suspect one of the parts you have changed.
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Old 02-23-2015, 06:34 AM
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Re: Noisy Belt? Please help!

I have not done that. I will as soon as I can get a partner to help me out. Can a new alternator have a bad bearing that is causing this? The belt isn't hot or glazed. I don't think it's the belt or the idler. So the alternator is the only thing new in the system.
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Old 02-23-2015, 06:44 AM
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Re: Noisy Belt? Please help!

It is always possible that a bad bearing was used in the new alternator. You can flip the throttle with your hand from the engine bay. Just check where the accelerator cable runs over the throttle blade sector. That part you can move by hand, eventhough its maybe not that easy to listen around at the same time.
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Old 02-23-2015, 06:48 AM
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Re: Noisy Belt? Please help!

I will check that out. It may be a few day though. I will get back with you. This has been driving me crazy! haha. I have heard the belt squeals at startup. I have heard them squeal under heavy load. I have heard the chirps. This is different. And it is so strange that you can manipulate it easily with the throttle and that it is only heard was the engine speed is going back down. Thank you so much for your help!
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