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Strange Braking Behavior

Discussion in 'Gen 2 Prius Main Forum' started by ibis315, Aug 6, 2007.

  1. ibis315

    ibis315 New Member

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    Has anyone felt the Prius accelerate while braking, especially when it hits a dip? I've felt this more than once. Moderate braking and one front wheel hit a small dip in the road. The Prius ICE speeds up and the car seems to accelerate instead of slowing down. Anyone else?
     
  2. Sufferin' Prius Envy

    Sufferin' Prius Envy Platinum Member

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    <div class='quotetop'>QUOTE(ibis315 @ Aug 6 2007, 11:28 AM) [snapback]491389[/snapback]</div>
    1) Your Prius is not accelerating under the condition you are describing. It is, however, not decelerating at the same rate for that fraction of a second when the braking system is sensing that bump or dip in the road as a condition in which it needs to correct with the ABS system.

    Yes, this has been described many times by many people here on PriusChat. It's not dangerous . . . unless your ICE is actually speeding up . . . which I doubt.

    2) What makes you say the "The Prius ICE speeds up"????
    It is a very quiet ICE under normal loads and there is no tach. Is this a seat of the pants "feeling" . . . or do you have a Scangage hooked-up to the car?

    Don't worry about it. Continue to brake normally. It is one of the funny little idiosyncrasies of the Prius.
     
  3. efusco

    efusco Moderator Emeritus
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    It doesn't accelerate, but the degree of deceleration decreases...giving the sensation of that affect.

    When braking moderately, if you hit a bump/pot-hole the regen braking will disengage, to get the exact same amount of friction braking the brake pedal needs to be depressed a little more.

    You're not gaining speed, you're just not losing speed as quickly as you were before the bump.
     
  4. Danny Hamilton

    Danny Hamilton Active Member

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    <div class='quotetop'>QUOTE(ibis315 @ Aug 6 2007, 01:28 PM) [snapback]491389[/snapback]</div>
    Nah, I haven't felt it accelerate while braking.

    I have felt it decelerate less quickly (if you aren't paying close enough attention, this can feel like acceleration) when anti-lock brakes kick in.
     
  5. slair

    slair Ubër Senior Member

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    Gas on the right, brake on the left. Just remember that....

    Just kidding, but couldn't resist. :p
     
  6. chogan

    chogan New Member

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    <div class='quotetop'>QUOTE(ibis315 @ Aug 6 2007, 02:28 PM) [snapback]491389[/snapback]</div>
    Same response as those above -- ABS is sensitive, cuts out the braking momentarily when you hit a bump in the road. I find it particularly true when headed downhill, and I've had the same thing happen when (e.g.) pulling onto the gravel shoulder of a road. Definitely scared me the first few times that happened, but 1) I've learned to avoid setting it off and 2) only rarely does it trigger unexpectedly and I now know what it is. I'd never had a car do this before I got a Prius. The good news is that you can both adjust your driving to avoid it and get used to it when it happens. It no longer bothers me (but I remain very cautious when pulling off the road.)
     
  7. Sufferin' Prius Envy

    Sufferin' Prius Envy Platinum Member

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    <div class='quotetop'>QUOTE(efusco @ Aug 6 2007, 11:42 AM) [snapback]491400[/snapback]</div>
    Do Oh, I think you may be correct. If the friction brakes aren't engaged, it wouldn't be the ABS system causing this sensation . . . unless the ABS also cuts-out the regen braking. :huh: Something way below my level of Priiknowledge to discern.