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Mushy Brakes

Discussion in 'Gen 2 Prius Main Forum' started by ml86, May 1, 2006.

  1. ml86

    ml86 New Member

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    My brake pedal easily goes down to within 1-2 inches of the floor, and I can just as easily push it to the floor. This concerns me. I have not had any actual braking problems, they seem firm enough in normal driving conditions. The local Prius mechanic says this is not unusual in any new cars, and the Prius has electronically operated brakes which he implies makes them even softer. Anyone else having this concern and/or have an experience or opinion to share?

    Merci beaucoup.

    (In support of undocumented Frenchmen everywhere).
     
    #1 ml86, May 1, 2006
  2. qbee42

    qbee42 My other car is a boat

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    <div class='quotetop'>QUOTE(Max Smart @ May 1 2006, 10:19 PM) [snapback]248322[/snapback]</div>
    No, my brakes feel very normal; not anywhere near that much travel in the pedal.

    Tom
     
    #2 qbee42, May 1, 2006
  3. ml86

    ml86 New Member

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    <div class='quotetop'>QUOTE(qbee42 @ May 1 2006, 09:58 PM) [snapback]248342[/snapback]</div>

    Thanks Tom. Appreciate it.
     
    #3 ml86, May 1, 2006
  4. tochatihu

    tochatihu Senior Member

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    I don't like what I'm reading here, Max Smart. No Prius brake pedal should push easily to the floor. You need to be talking to a different Toyota shop, the "Sooner" the better! Please start by lifting the hood and confirming that the brake fluid reservoir is filled to between the marks. The fluid you see inside should have a "light straw color".
     
    #4 tochatihu, May 1, 2006
  5. hobbit

    hobbit Senior Member

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    You've probably got too much air in the system, or there's a leak
    someplace. Check the brake fluid level in the white plastic
    reservoir under the hood on the right side near the strut tower.
    Have the dealer-tech bleed the system and check it for leaks.
    Bleeding air out of this system is a rather complex procedure, and
    easy for someone to have screwed up.
    .
    _H*
     
    #5 hobbit, May 2, 2006
  6. ml86

    ml86 New Member

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    Yeah, I kick myself for jawing about EV mod switches and then forgetting to insist he at least crawl in and pump the pedal. I'll check the fluid and then take it to another dealer. Maybe back and have him pump them. Sooner than later.

    I needed some "pumping up" to take it seriously I guess. It's the only thing I can find to worry about, except a small rattle. Brakes are a big worry though.

    Thanks.
     
    #6 ml86, May 2, 2006
  7. saechaka

    saechaka Member

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    #7 saechaka, May 2, 2006
  8. ml86

    ml86 New Member

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    Regarding my mushy brakes,

    I had another tech actually drive the car today. He says the brakes are fine. He offered up a more detailed but similar explanation regarding my experience as the previous tech did. The brake pedal actually does not activate the brakes directly, so no hydraulic pressure build up (my interpretation) that one normally feels. The brake pedal actually is only spring activated, or the spring provides the resistance I guess. The brake pedal position is associated/connected to an electronic device that then activates the brakes and determines the braking intensity. So the brake will not actually feel the same, and being able to push the pedal to the floorboard when at a complete stop doesn't mean a thing. I checked the fluids and they are indeed fine.

    But even so, for me it is a bit unnerving and will take some getting use to.

    Thanks for the feedback.

    [attachmentid=3208]
     
    #8 ml86, May 2, 2006
  9. tomdeimos

    tomdeimos New Member

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    My brakes are not mushy at all and if you brake in neutral they should feel and work just like any other car's hydraulic brakes. The pedal on mine does not go anywhere near the floor even if I lock the wheels (at least till the anti-skid takes over).

    The regen braking does feel different if you brake normally in drive, but I would not ever call it mushy.
    If it was I would not drive the car.
     
    #9 tomdeimos, May 2, 2006
  10. saechaka

    saechaka Member

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    <div class='quotetop'>QUOTE(Max Smart @ May 2 2006, 06:07 PM) [snapback]248784[/snapback]</div>

    well, as long as your under warranty your good. but your brakes should not be mushy as mine were until they fixed the "actuator thingy" maybe you should ask him to compare it to another prius
     
    #10 saechaka, May 2, 2006
  11. ml86

    ml86 New Member

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    <div class='quotetop'>QUOTE(tomdeimos @ May 2 2006, 08:11 PM) [snapback]248825[/snapback]</div>
    That is the experience I'd like to have but I'm not sure how to reconcil it with the info from tech. Maybe while in OKC I'll visit a dealer and test their cars too.

    Thanks.
     
    #11 ml86, May 2, 2006
  12. hobbit

    hobbit Senior Member

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    "... only spring activated ..."
    Not quite. Hydraulic pressure *does* build up, but only in the
    stroke simulator. That is, effectively, a spring, although you push
    on it via brake fluid and not directly with the pedal. The pressure
    in that system is a measure of how hard you're pressing, and is sent
    to the hybrid system as the amount of braking request. The hybrid
    ECU and the skid-control ECU go off and have a secret conference
    about how much each is willing to contribute to meet the demand,
    and come back with a proportion of regen and a proportion of physical
    wheel brakes. If you do it right, the answer is usually 100% regen.
    .
    But the request *is* transmitted hydraulically, it just doesn't
    reach the wheels until later on. The pot connected to the pedal
    pivot is largely for sensing *onset speed* of braking, not the
    absolute position -- that's what detects panic stops.
    .
    It is conceivable that air bubbles between master cylinder and the
    stroke simulator would cause "mushiness". Again, have it bled.
    .
    http://techno-fandom.org/~hobbit/cars/bp/BPP-system.gif
    http://techno-fandom.org/~hobbit/cars/cours-section6.pdf
    .
    _H*
     
    #12 hobbit, May 3, 2006
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