Sound strictly proportional to speed

Discussion in 'Generation 1 Prius Discussion' started by anon61, Aug 27, 2017.

  1. anon61

    anon61 Junior Member

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    After the inverter coolant problem, Apparently the 12v generator quits after a few minutes | PriusChat, my car has developed a loud noise. It is strictly proportional to speed. I can hear from 30 kph/20mph and it gets louder as I go faster. Putting it into neutral does not make the sound go away. I have put a recording I made with my phone on dropbox:

    Dropbox - Inspelning_170806.mp3

    Searching a bit in the forum I find three candidates
    1) Wheel bearing
    2) MG2
    3) Transaxle

    How do I proceed to find out what it is? I have a OBD dongle and Torque on my phone, if that would help.
     
  2. SFO

    SFO Active Member

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    Though I didn't listen to the mp3, this sounds like a wheel bearing issue.

    One way to check for wheel bearing wear is to jack the wheel in question and hold it at 3 and 9 (on the clock) then give it a push/pull (push at 3, pull at 9), then do it the other way. Now do the same motion at 12 and 6 on the clock. If you feel that it is not solid or if there is any play then you've found the bearing.

    How many miles are on this gen1 vehicle?
     
  3. Sam Spade

    Sam Spade Senior Member

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    It also can be a simple matter of a dragging brake pad......or something like a rock lodged between rotor and pad.
     
    #3 Sam Spade, Aug 27, 2017
    Last edited: Aug 27, 2017
  4. ChapmanF

    ChapmanF Senior Member

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    When my Gen 1 wheel bearings went (I ended up replacing two of them, the first around 160k if I recall correctly, the second three years later), it was pretty hard to identify the failing ones by feel at first. There was not any play that could be felt by pushing/pulling on the wheel.

    The first one eventually got bad enough to feel grotty when spinning the hub by hand, so that was a positive ID. The second one defied every tactic for identifying it short of a ChassisEar (four clamp-on microphones and a wireless four channel receiver you take in the car with you for a test drive). That worked great, and id'd the failing bearing in seconds.

    You're probably most eager to differentiate bearing failure from MG2 failure (both would make noises that continue even in neutral). If you can make out a pitch for the sound you are hearing at a known road speed, and compare it to a tuner (unless you have perfect pitch!), you can do some math to see if you are hearing a harmonic of the MG2 rpm. "No" is the answer you'd prefer, because MG2 failure is a pain.

    My Gen 1's front wheel bearing was sounding a frequency around 12.8 times the wheel rpm
    (that is, g, c, and d on a tuner, just slightly flat, at 30, 40, and 45 MPH on stock tires), which I was able to explain from the bearing geometry after getting the old bearing apart and getting some measurements.

    When I had replaced the rear bearing earlier, what I was hearing was e, a, and b, again just slightly flat, at 30, 40, and 45 MPH, or a ratio of 10.8 times wheel RPMā€”but I never took that bearing apart to see if I could confirm that ratio from its geometry.

    I guess I would caution that bearings can make lots of noises that don't sound like a discernible pitch at all, and even if there is a pitch, it might depend on the location of the defect. The 12.8 ratio I was hearing with the front bearing is what you'd expect for a defect in the outer race. Different defects, maybe different sounds.

    All the pitches I mention here should be taken as purely specific to Gen 1; I've never compared the dimensions of any other generation Prius bearings.

    -Chap
     
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  5. anon61

    anon61 Junior Member

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    SFO, it has 256000km on the clock, that is 160000 miles. I checked the wheels but I could not feel any play.

    Sam, a rock lodged, you mean between brake disk and pad, or drum and pad?

    Chap, I read you post. I don't think this sound is clear tone in that way. Also, I don't think it is an octave higher at 80kpg than at 40kph

    I checked the MG temps after a short drive, and I got 44 celsius in MG1, and 38 in MG2.
     
  6. Sam Spade

    Sam Spade Senior Member

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    Yes. Either.

    Many brake pads also have "wear indicators" that start squealing when they approach being worn out.

    Have you spun the wheels with the car off the ground ??
     
  7. anon61

    anon61 Junior Member

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    I took the car to Toyota, and they say at least the front left wheel bearing needs to be replaced. They say they can't diagnose the back bearings, since the rusty brakes make too much noise. So they want to replace all disks and brake pads. They quoted me about 1500 USD for that.

    The brakes seem to be the weakest point in my car. They probably get used too little, it is a hybrid, I don't drive much, and lets say that my driving style is a very good fit to the performance profile of the Prius. Perhaps if I'd known about the braking in neutral trick from the start I would have had less problems with it.

    I am thinking that this the end of this car. Now the question is, a newer Prius or a biogas vehicle?
     
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  8. FireFighterHill

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    Where are you located? Replacing the rotors, pads, shoes, and drums isn't hard. I even replaced the wheel cylinders, brakes hoses and calipers on mine.
     
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  9. Brian in Tucson

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    Replacing all the brakes is not too bad, or expensive if you get aftermarket and don't use the inflated prices for labor at the Toyota dealer. I don't know the aftermarket sources for Sweden, but even if you had to import them from Germany or the UK, it would be better than buying them from the dealer. Here in the US, I'd get them from Rock auto dot com. BTW. replacement wheel bearings are quite cheap and the hubs are not too tough to rebuild. You may have to have a machine shop press the old ones out and press the new ones in.
     
    #9 Brian in Tucson, Oct 12, 2017
    Last edited: Oct 12, 2017
  10. Sam Spade

    Sam Spade Senior Member

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    It would be for anyone who has trouble screwing in a light bulb.
    (not referring to anyone in this discussion, of course!!)
     
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