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"Lunging" while braking with weak traction

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Frogerelli, May 22, 2013.

  1. Frogerelli

    Frogerelli Junior Member

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    As in lunge.

    I first noticed this about two months ago (I bought the car three months ago) when I was braking on straight, level ground, but it was raining and I was crossing railroad tracks while I was braking. Fortunately, no one was in front of me. The sensation wasn't merely a loss of braking traction (sliding), this felt like a momentary, power mode/full throttle thrust. Straight forward. At the time, I was clearly caught off guard, but the effect/sensation was quite momentary, almost as if someone had mildly rear-ended me.

    Braking after that moment was normal.

    The effect didn't replicate itself again until recently when I was braking for a stoplight on a sh-tty concrete road where the sections have a slight tilt to them. This is exaggerated of course, but the sections are like this: ///////, meaning there is a 1/4 to 1" dropoff from one section to the next. there is one particularly pronounced dropoff close to the stoplight. The effect happened again and it is reproducible. Again, it is not merely the sensation of taking your foot off the brake, but one of a momentary punch of acceleration. No appreciable sound of higher engine revs.

    Anyone else experience this?
     
    #1 Frogerelli, May 22, 2013
  2. matt b.

    matt b. Member

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    is not happening to me but the year of your Prius there was are brake recall I would suggest that you take it in to the dealer. you could also contact ur nearest toyota dealer and give them your vin and they can see whether or not your car is one that has been recalled hope this helps.
     
    #2 matt b., May 22, 2013
  3. Les_PL

    Les_PL Active Member

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    #3 Les_PL, May 22, 2013
  4. Codyroo

    Codyroo Senior Member

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    This is a known "experience" with the Prius braking system and there are a number of threads discussing it.

    Prius Brake Problem - CONFIRMED BY TECH | PriusChat

    This typically happens under light braking when are just using regen braking instead of regen brakes AND the disc brakes. The car senses that your wheels are slipping and reduces braking to prevent a skid. The sensation feels like you are surging forward.

    I've had this happen to me once or twice and it gives a nice adrenaline rush!
     
    #4 Codyroo, May 22, 2013
  5. car compulsive

    car compulsive Active Member

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    Yep, one of the quirks of this car - along with the loss of most thrust when you take off on gravel or ice and wheel spin is detected. Give yourself more braking distance and DON'T lift your foot off the brake and try to pump them (like us old guys were taught back when Moses was a boy).
     
    #5 car compulsive, May 22, 2013
    spiderman likes this.
  6. Lynette

    Lynette New Member

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    Yes....several times when I have braked while going over an uneven surface or bump I have felt a lunge forward. I thought I was imagining the movement because it is only for a slight moment. After several observations I decided to come on to this forum to see if anyone else has had this problem. Has anyone mentioned this to the service department at the dealer?
     
    #6 Lynette, Aug 20, 2013
  7. 32kcolors

    32kcolors Senior Member

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    It's a common and normal characteristic of regenerative braking that you simply need to get used to.
     
    #7 32kcolors, Aug 20, 2013
  8. Frogerelli

    Frogerelli Junior Member

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    Get used to it? I'm resigned to it for this vehicle, but every one of us should not be.

    A response time of 1/100th of a second is easily achievable. That is what was the standard response time for a 2004 Lexus active suspension. There is no reason the technology of this response time (or much faster) should not have trickled down in 6 years to be applied to regenerative/conventional braking. It's the same corporation, after all; there shouldn't even be any costs of licensing the technology.

    Toleration begets lack of innovation.
     
    #8 Frogerelli, Sep 19, 2013
  9. Frogerelli

    Frogerelli Junior Member

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    30 mph equals 44 feet per second. Think how long it takes for the the system to switch and remember that it always happens in sub-optimal situations. Do you have 22-33 feet to spare?
     
    #9 Frogerelli, Sep 19, 2013
  10. hlunde

    hlunde Member

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    Actually, I believe that the initial sensation is due to a purely mechanical effect -- braking torque being applied at the transaxle output shaft through a mechanical differential, so if one wheel slips, the other cannot generate torque. At this point the ABS kicks in. A positive aspect is that the driver's foot is already on the brake pedal, so the application of additional pedal force (thus transitioning to friction braking) is rather swift. An MG on the rear wheels would readily address this issue.

    That said, I am continually aware of the regenerative braking effect and always brake more cautiously with the Prius. The gear whine from regenerative braking is my key.
     
    #10 hlunde, Sep 20, 2013
  11. Mide

    Mide Junior Member

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    Yup I've had this happen to be as well before I read about it on the forums. I was lucky that I gave myself enough room after the pothole to have distance from the car in front of me or else I would've rear-ended him. Just got to be careful.

    I looked up my VIN number with some recall a while ago but it can up empty so I doubt Toyota will help out any.
     
    #11 Mide, Sep 20, 2013
  12. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Doesn't happen if you get the recall done. That was the recall done about a year ago.
     
    #12 GrumpyCabbie, Sep 20, 2013
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