Hissing sound from rear breaks when breaking

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by icyrius, Jan 30, 2021.

  1. icyrius

    icyrius Active Member

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    Hello. Yesterday I drove in my son’s Gen 3 and noticed his rear breaks make a hissing sound every time he pressed the breaks at low speeds.
    I own a Prius V and my brakes only do that when I first start my car in the morning when the gas engine has not started. Once the gas engine starts, I guess the break fluid gets circulating and the metal to metal rear breaks sound stops in my car.
    I am under the impression that my son’s car is not getting that break pump pressure. It sounds as if only metal to metal breaking force is happening.
    Is there a way to check or lube a part that might be sticking in the back?
    Thanks
     
    #1 icyrius, Jan 30, 2021
  2. bisco

    bisco cookie crumbler

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    not sure what you mean by a hissing sound. you should hear a buzzing sound under the hood when you open the drivers door, that is the brake pump. and also at various time s when stepping on the brakes as needed to keep pressure up, although this is less noticeable because you are driving.

    any sound from the rear brakes requires an inspection. it may be that new pads are needed, and you are hearing the wear indicators, or it may be something else.
    it is confusing that you hear the same sound in your car, but less often.
     
    #2 bisco, Jan 30, 2021
  3. ASRDogman

    ASRDogman Senior Member

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    It could be that you are not use to the different sound his car makes.
    How many miles on the car? How does he drive.
    You should easily get well over 100,000 miles out the the brake pads.
    But worth pulling the wheels and checking the thickness of the pad, and check the
    rotors for any grooves....

     
    #3 ASRDogman, Jan 30, 2021
  4. ChapmanF

    ChapmanF Senior Member

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    I don't know if 'hissing' is the word I would use, but I expect you're talking about the friction sound made by the pads against the rotor when the car has been sitting a bit and there is some flash rust on the rotor surface.

    The pads scrub the flash rust off the rotor over the first few stops and the sound is quieter after that.

    Brake fluid doesn't 'circulate' to the brakes; those four brake lines are dead ends. The brake fluid in those calipers was the first brake fluid that was poured into the car when the lines were bled at the factory, unless it's been flushed since.

    There isn't any 'metal to metal' contact going on; brake fluid isn't like oil in a bearing. The brake pads have a non-metal friction lining bonded to a metal backing, and the only time any 'metal to metal' action would happen is when that friction lining has completely worn away. Pads are s'posed to be changed before that happens. If it does happen, it's a metal-to-metal grind that does not go away until the grinding parts are replaced.
     
    #4 ChapmanF, Jan 30, 2021
  5. icyrius

    icyrius Active Member

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    Thanks for your reply. Car has 130K miles and he told me that in his last Toyota service visit they told him that “he was getting there” for a break service.
    Here do I check the rear brakes?
     
    #5 icyrius, Jan 30, 2021
  6. icyrius

    icyrius Active Member

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    Thank you so much for this thorough explanation. It is very true his car has been sitting in my driveway without being driven. My son left on a trip and left his car with me. It’s been a couple of weeks since it had been driven. it is probably the rust as you mentioned. Today I plan to drive it all day and see if it goes away.
     
    #6 icyrius, Jan 30, 2021
  7. bisco

    bisco cookie crumbler

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    yu would have to pull the wheels and measure the pad thickness, and inspect the rotors for grooving or runout
     
    #7 bisco, Jan 30, 2021
  8. icyrius

    icyrius Active Member

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    Yesterday I drove the Prius all day and longer distances than a quick trip to the nearest supermarket. I am very glad to say that the sound was almost totally gone. Thanks again for all your help.
     
    #8 icyrius, Jan 31, 2021
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