Cause of whine/squeal around 3500 rpm

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    Author Topic: Cause of whine/squeal around 3500 rpm  (Read 1552 times)

    Offline 71HemiCuda

    • 1971 Hemi Cuda
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    Cause of whine/squeal around 3500 rpm
    « on: June 04, 2019 - 12:18:41 PM »
    My 71 Hemi Cuda emits what I want to say is more of a whine (rather than a squeak) at around 3500 rpm when driving it aggressively. Pretty sure it isn't a belt squeak as I tried putting belt dressing on and it and it didn't make a difference. My guess is that the bearings in the alternator is what is making the noise but I want to get opinions from others before purchasing a new alternator. I suppose it could also be coming from the water pump. FYI - the alternator is a single pulley as there is no a/c. Thanks in advance for any opinions.
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    Daryl - Maplewood MN - 1971 426 Hemi Cuda, 4 speed pistol grip, Sassy Grass Green


    Offline 70chall440

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #1 on: June 04, 2019 - 01:50:14 PM »
    Does the car have power steering? In my experience, this is more times than not the cause of errant whines although the alternator can be as well. Sometimes you can differentiate between the 2 by flipping on the lights when you hear it; sometimes it will go away and sometimes it will get louder if it is the alternator. Can you replicate the whine while stationary by rev'ing the motor?
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    Offline 71HemiCuda

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #2 on: June 04, 2019 - 02:29:19 PM »
    Quote from: 70chall440 on June 04, 2019 - 01:50:14 PM
    Does the car have power steering? In my experience, this is more times than not the cause of errant whines although the alternator can be as well. Sometimes you can differentiate between the 2 by flipping on the lights when you hear it; sometimes it will go away and sometimes it will get louder if it is the alternator. Can you replicate the whine while stationary by rev'ing the motor?


    No, it doesn’t have power steering and yes, I can duplicate it by just revving the motor.
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    Daryl - Maplewood MN - 1971 426 Hemi Cuda, 4 speed pistol grip, Sassy Grass Green

    Offline 70chall440

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #3 on: June 04, 2019 - 10:46:29 PM »
    Ok, so then you are pretty sure its the alternator?
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    Current Mopar
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    Offline jimynick

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #4 on: June 04, 2019 - 11:55:25 PM »
    Take the alternator v-belt off and see if it still makes the noise. That'll help eliminate some variables. Check the PS fluid levels and make sure it's got the correct type and amount of fluid, too. Good luck  :cheers:
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    Offline 70chall440

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #5 on: June 05, 2019 - 11:52:33 AM »
    Jimy... got to stop skip reading..  :bigsmile: car doesnt have PS, manual steering car. But your point is on point; Id remove the belt and see if the whine is gone just to make sure. I once heard a car that had a high pitched whine, almost like a supercharger but it didn't have one. After some investigation, the only thing we could think of was the timing chain; we opened it up and replaced the timing chain and sprockets; whine went away. Not sure why it was whining, just know the noise went away.
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    Current Mopar
    70 Challenger RT 440-6 EFI, 73 Cuda 416-6 EFI
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    Offline jimynick

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #6 on: June 05, 2019 - 02:22:38 PM »
    LOL! Yup!
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    Offline 71HemiCuda

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #7 on: June 06, 2019 - 12:11:55 PM »
    The noise stops when I remove the belt so I'm guessing that means it is either the alternator or the water pump. I assume the water pump could also be making the noise since it also has bearings that can go bad. Is there any way for me to tell for sure which one it is? I am guessing it is the alternator as there are no other signs that the water pump is going bad, but would like to know for sure.
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    Daryl - Maplewood MN - 1971 426 Hemi Cuda, 4 speed pistol grip, Sassy Grass Green

    Offline 70chall440

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #8 on: June 06, 2019 - 05:49:58 PM »
    normally if it is the WP, the shaft will be loose, spin it by hand, wiggle it, if no movement and it spins freely, it is probably not your problem. take the alternator to your local parts store and see if they have the testing machine, it spins the alternator and perhaps you can confirm that way as well.
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    Current Mopar
    70 Challenger RT 440-6 EFI, 73 Cuda 416-6 EFI
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    9 x Challengers. AAR Cuda, 4 RR, 2 GTX, 4 Chargers, etc... (too many to list)

    Offline jimynick

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    Re: Cause of whine/squeal around 3500 rpm
    « Reply #9 on: June 06, 2019 - 10:47:23 PM »
    Yep, what the man said. If you grab the fan and try to move it back and forth both vertically and horizontally and feel movement, that's a clue. Sometimes you can hold the pulley of an alternator and turn it by hand while putting a bit of side pressure on it, feeling for ANY roughness and it may also tell you a story. If you take a piece of welding rod and put your thumb over the one end and place that thumb against your ear while placing the other end onto the case of the alternator while it's being spun, you can do a poor man's stethoscope if you don't have a real one. You'll hear it if the bearing's pooched. 
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