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Rain and the Brakes...

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Matt H, Jun 7, 2015.

  1. Matt H

    Matt H Active Member

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    Just wondering how many other C owners are experiencing harsh transition when the hydraulic brakes take over, just as the car comes to a stop, when it's wet outside...

    There's a delicate balance just when you're coming to a stop with mild pedal pressure. MG2 regen. braking tapers off, and at the same time, the hydraulic brake system applies the brakes. Do this at a low enough speed, with little pressure, like creeping forward in traffic, and the brakes grab pretty harshly... Seen in on a few Aqua's now, but only when it's raining. The transition is seamless in the dry.
     
    #1 Matt H, Jun 7, 2015
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    As if the brakes were grabby?
     
    #2 Tideland Prius, Jun 7, 2015
  3. Super Mario

    Super Mario Member

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    Yes this happens to me when it rain but only for the first few stops then after it goes back to normal. On another note... My C did it all the time until I had her services at 30,000 miles and the dealer said they recommend a brake fluid flush. I had it done and now it only does it when it rains like I said above. The brake flush did help a lot for some reason.
     
    #3 Super Mario, Jun 8, 2015
  4. Tideland Prius

    Tideland Prius Moderator of the North
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    Weird. I know the brakes can be grabby on the Gen 2 because the discs are wet (especially if you brake gently all the time). The reason why it goes back to normal after a few stops is because the brake pads are slowly drying the discs. You won't notice it on non-hybrids because they always use the brake pads to slow the car down, while on a Prius (or any vehicle with regenerative braking), you're using the electric motor to slow the car down and only use the brake pads at the last bit before coming to a complete stop so the brake pads don't have the friction (and thus heat) to dry the pads on the first stop.
     
    #4 Tideland Prius, Jun 8, 2015
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  5. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Sometimes after washing the car it'll sit for a day or two before driving, and the brake discs start rusting up. For the first few blocks of driving they're kinda noisy, and I hear light scraping, with every application of brakes.

    Maybe I'm missing something, but what I glean from that is that the division of braking between the pads and the transaxle is not either-or, that there's always some degree of friction braking happening.
     
    #5 Mendel Leisk, Jun 8, 2015
  6. Super Mario

    Super Mario Member

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    Mendel that's normal. It's just the brakes clearing the rust off
     
    #6 Super Mario, Jun 8, 2015
  7. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    I understand, just thinking this noise illustrates that the conventional brake pads are in use pretty much all the time, at least to some degree. If the braking was completely handled by the motor/generators, you wouldn't be hearing the rust scuffing with every brake pedal depress.
     
    #7 Mendel Leisk, Jun 8, 2015
  8. valde3

    valde3 Senior Member

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    Prius always puts very some pressure to brakes when braking. http://hiwaay.net/~bzwilson/prius/zvw30_brake_010.jpg

    But that same pressure that makes rusted and dry brakes to generate noise and generate substantial braking force won’t really even dry the wet and smooth brake discs.
     
    #8 valde3, Jun 9, 2015
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  9. Tideland Prius

    Tideland Prius Moderator of the North
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    Didn't use to be the case. The pads would stay off if you brake lightly until the last bit (using the same method as you did - listening for that that noise of brake pads rubbing against the rusted discs). Maybe they changed it with that "brake recall".
     
    #9 Tideland Prius, Jun 9, 2015
  10. ChapmanF

    ChapmanF Senior Member

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    This is a PriusChat-famous issue for all Prii, in fact it (and the solution) were probably the very first things I learned from PriusChat when I bought my Gen 1.

    Getting in the car after wet weather? Brakes noisy and/or grabby? Make two or three stops from a moderate neighborhood speed, in neutral. Neutral keeps regen out of the picture so those are pure hydraulic stops. Silent again as the day you bought the car. Works every time. :)

    It's just a Prius-driving routine.

    -Chap
     
    #10 ChapmanF, Jun 9, 2015
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