Low pitch humming from front

Discussion in 'Gen 2 Prius Technical Discussion' started by Lodrun, Jun 18, 2019.

  1. Lodrun

    Lodrun My proper car is an MGC

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    For the past sixth months, my 2007 Toyota Prius (Gen 2, 77,000 miles) has been generating a significant low pitched humming sound somewhere from the front. The sound begins at about 30 mph then steadily increases in pitch and volume as speed increases. It is directly related to the rotation of the wheels. The car used to be very quiet at 70 mph, but is now significantly noisy, due to this intrusive sound. I suspected a wheel bearing, but my garage assured me that the bearings were fine and that the sound was coming from the tyres, which were near the end of their lives. Last week I replaced all four tyres, but the sound is still there.
    What could it be?
     
  2. Skibob

    Skibob Senior Member

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    When you get it up to 70 throw it in neutral and see if the sound goes away.
     
  3. bisco

    bisco cookie crumbler

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    sounds like wheel bearing. does the sound change when turning?

    how many miles on her?

    how did the shop go about making sure the bearings were fine?
     
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  4. ChapmanF

    ChapmanF Senior Member

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    I had a front wheel bearing that was really only successfully identified using a ChassisEar. It would make noise while driving, but nothing else anybody ever suggested was able to distinguish it from a good bearing.

    The ChassisEar solved the mystery in about three seconds (after setting it up, which of course took longer).
     
  5. padroo

    padroo Senior Member

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    Try jacking up the front of the car and run it while the wheels are off the ground.


     
    #5 padroo, Jun 18, 2019
    Last edited: Jun 18, 2019
  6. ChapmanF

    ChapmanF Senior Member

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    Mine seemed perfectly fine that way. It seemed perfectly fine comparing temperatures. It seemed perfectly fine jacking up and spinning by hand, jacking up and trying to wiggle, every other easy suggestion anybody gave me.

    It only made noise when actually driving, on the road, with full weight on it. And after hooking up the ChassisEar, the noise was completely unmistakable. It solved the case when nothing else did.
     
  7. Skibob

    Skibob Senior Member

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    What is a chassis ear?
     
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  8. WilDavis

    WilDavis Senior Member

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  9. edthefox5

    edthefox5 Senior Member

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    Probably bad wheel bearing really common on the G2 I had one do that at 30,000 miles on my bought new in 07. Was fixed for free under 3/36 warranty. Many many posts about it use search forum.

    Real simple to test. Get up to speed and turn briskly one direction or the other and note the noise. If right turn makes the noise worse its the drivers side bearing. Vice versa.
     
  10. bisco

    bisco cookie crumbler

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    huh, i thought turning was the test for cv joints
     
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  11. edthefox5

    edthefox5 Senior Member

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    Turning is best for wheel bearings too. When you make a hard turn it puts significant load on the wheel your pivoting on and will expose a bad wb.
     
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  12. ChapmanF

    ChapmanF Senior Member

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    It's still possible to get a weird one like my old left front, which didn't cooperate with any of the "it's easy, just do this and you'll immediately know" ideas. If that happens, I can vouch for the ChassisEar to make short work of the mystery.
     
  13. WilDavis

    WilDavis Senior Member

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    Nah! I always thought the Turing Test to be a test of a machine's ability to exhibit intelligent equivalent to, or indistinguishable from, that of a human. :rolleyes:
    Faced with "Low pitched humming" You might try hanging the words where they can be seen! (…rim shot!)
     
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  14. jimolson

    jimolson Junior Member

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    As an owner of two Gen II Priuses and helper to owners of three others, I've replaced (or helped replace) qty=5 front wheel bearings.

    The telltale noise is a low rumble whose pitch tracks road speed. It sounds like a tire with worn tread.

    I agree that the noise is similar to the sound of a CV joint, and that usually it gets louder or softer as you rock the steering wheel from side to side.

    None of the bearings I replaced could be diagnosed with the vehicle jacked up. All required road tests to diagnose. Usually the low rumble gets undeniably worse within 5k miles of inception, turning into a loud grinding noise.

    However, one worn but recalcitrant bearing remained at a low rumble for nearly 10k miles without developing the grinding noise.

    The average odometer reading of bearings I replaced was in the 100k to 140k mile range. One bearing I replaced twice.
     
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