First Panic Stop today - NOT good!!

Discussion in 'Gen 4 Prius Technical Discussion' started by Zardoz, Sep 16, 2017.

  1. Zardoz

    Zardoz Member

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    Traffic came to a sudden stop on the freeway today forcing me to hit the brakes hard from about 30mph. My Pius 2 stopped like an unloaded pickup truck! With a full tank of gas, the rear brakes pulsed from the ABS and it seemed that the front brakes did not try hard enough to stop the car.

    Is this normal? Is this balance issue adjustable?

    Thanks!
     
  2. alanclarkeau

    alanclarkeau Senior Member

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    Why do you wonder if this is abnormal - did the car not stop in time??

    I'm not sure about a Gen4 Prius, but the front/rear balance of a 2010 Prius is - Front: 830kg/Rear: 530kg. Panic stops on my recent Front Wheel Drive cars have normally had the ABS working hard to stop the rear wheels particularly from locking up. It will depend on the load, number (and mass) of passengers, but more to do with the road surface.
     
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  3. Zardoz

    Zardoz Member

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    I am used to driving my 2005 Prius. It was MUCH more predictable!
     
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  4. Elektroingenieur

    Elektroingenieur Senior Member

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    It’s similar for the fourth-generation Prius. For one model, the unladen weight is 850 kg (1874 lb) on the front axle and 540 kg (1191 lb) on the rear axle. (These figures are from the Japanese edition of Toyota’s New Car Features book; interestingly, the U.S. and European editions give only the total gross weight.)
    I don’t know of any customizable parameters or settings for the electronically controlled brake system; its behavior is defined by the software in the skid control ECU. There are initialization and calibration procedures in the Repair Manual, but these are normally done only when parts are replaced, and they proceed automatically, with no opportunity for adjustments by the technician.

    A record of the braking event might still be stored in the Vehicle Control History, which can be retrieved using a Toyota Techstream diagnostic system, but I’m not sure this would be of much use without access to engineering design information that Toyota hasn’t published.
     
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  5. alanclarkeau

    alanclarkeau Senior Member

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    Thanks, I couldn't find a F/R balance Australian figure either. But that balance is fairly typical of a Front Wheel Drive car +/-.

    It's very difficult to describe braking, and no 2 cars or brake events will be the same. I've done a few panic stops from much higher speeds in my 2016, and never felt it was abnormal. That's bearing in mind that my previous 2 cars were sportier cars and had sports type lower profile tyres with which I would expect superior grip.

    The computer ABS and Stability Control generally do a great job, and could have been intervening in the OP's case to enable all 4 wheels to take some of the braking load - did Gen 2 PRIUS have stability control?

    Grip on the road can make a big difference. I do remember one situation in my FORD Fiesta while braking moderately hard on a wet road I ran over a manhole cover - the car twitched as first front then rear wheels lost grip, but I kept steering straight, and could sense the computer correcting the car - it did a slight wiggle, but ended up straight and stopped in time.
     
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  6. Just.Drive.It.

    Just.Drive.It. New Member

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    Brakes. That's the one area of my Prius that is very odd. The braking feel seems to change every day. Or every hour! One minute, the brakes will stop on a dime. Nice and firm and solid. And then a few minutes later, it seems like the pedal goes all the way to the floor, and the stopping action feels very weak and mushy. Never know what to expect.

    Brake inspection shows no problems. The brakes act odd on all various kinds of road surfaces. So I can't blame it on the road. I've stopped trying to figure out this car. It is just strange Prius technology.
    So, I fuel it up, and just drive it!
     
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  7. Zardoz

    Zardoz Member

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    Yes, mine had stability control.
     
  8. fotomoto

    fotomoto Senior Member

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    Once the brakes are bedded in on a new car, one should practice multiple maximum stops to find out what the new "normal" is and not wait till a panic situation occurs.
     
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  9. bisco

    bisco cookie crumbler

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    just drive it.
     
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  10. alanclarkeau

    alanclarkeau Senior Member

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    Agreed - when my children were learning to drive, I found a safe wide deserted wet road and had them do panic stops, starting from slow speed. We had a RWD Japanese small van as well as a FWD car - and they learned that they behaved VERRRRRY differently.

    By the time my last child started learning, we had ABS on my VOLVO - which was very offputting when she first hit the brakes hard - she released the pedal as it chattered away - by the 3rd try, she realised you just keep it hard down and ignore the noise.
     
    #10 alanclarkeau, Sep 17, 2017
    Last edited: Sep 17, 2017
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  11. drysider

    drysider Active Member

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    I am assuming from the post that you stopped in time. That really defines a "good stop" to me. Any one you walk away from.....
     
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  12. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    Once after getting a brake fluid change done (car with rear drums) they managed to leave one rear corner disabled. Handed it back to me without a test drive, so much for professionalism...

    Anyway, it was a car I wasn't that familiar with, and it felt a little off, but i figured I just wasn't used to it. There was an odd side-to-side rocking just as it stopped, and it seem to take inordinately long/hard effort.

    Heading towards an intersection with traffic light I got a yellow, decided to stop for it. Thought it was all good, but ended up almost across the crosswalk, with the anti-lock brakes going off like crazy.

    Long story short, I raised the rear end, tried spinning both wheels while my wife pressed the brakes, and what ho...

    They redid it, twice, and thoroughly test drove it. And replaced the bleed screw caps they'd lost the first time 'round, lol.

    Moral of the story, I guess: there COULD be a problem. Unlikely with a new car, but it shouldn't be discounted completely. You could get a dealership mechanic to test drive, see what they think.

    And/or test drive a loaner if possible, to compare.
     
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  13. kithmo

    kithmo Couch Potato

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    What puzzles me is how you get in a panic stop situation on a freeway and from 30 mph, was it foggy ?
     
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  14. Jorin

    Jorin Member

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    Last year my wife did what you call a panic stop on german Autobahn. The traffic on the left lane came to a full stop out of nowhere, right after a knoll (right word for it? Google told me). We were driving fast, something around 160 km/h (99 mph). She reacted perfect, hammering her foot on the brakes, ignoring the ABS stutter. She did make a swerve to the right, because the Mercedes behind us was too close - he did a swerve to the left himself, which prevented a collision with us. Thanks to the braking system of the Prius nothing else happened. We came to a full stop without hitting someone. But it was real close!

    I am driving the car for a year and a half now and I am driving it fast. No bad experiences with the brakes till now, except the noises in low speed till complete stop. But that aren't the brakes.
     
    #14 Jorin, Sep 18, 2017
    Last edited: Sep 18, 2017
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  15. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    OMG that's fast. Are you obligated to drive thus?

    (We rarely get over 90 kmh, intentionally use secondary highways when possible.)
     
  16. Jorin

    Jorin Member

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    We are the only country in the European Union without a general speed limit on our highways, which are called Autobahn. Reference speed is 130 km/h though. Most of the time this missing speed limit means stress, so I would prefer we had one. We have highways with four lanes, but also with three or only two lanes. Imagine a lot of trucks on the right lane driving with around 90 km/h and the rest drives on the left lane, as fast as possible or allowed. Can be a dangerous situation. But sometimes you must consider: driving with the trucks in the right lane (which can be frustrating) or driving along with the powerful BMWs, Audis and Mercedes in the left lane.
     
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  17. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    I'll take frustrated, with the trucks, lol. Yeah the Autobahn is (in)famous for vague speed limits, even back when I was young I think.

    Sadly, higher limits and/or disregard of limits are popular now.
     
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  18. pilotgrrl

    pilotgrrl Senior Member

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    That reminds me, what is the weight and velocity of an unladen swallow?
     
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  19. Tideland Prius

    Tideland Prius Moderator of the North
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    When you're in a BMW, MB or Audi that is built for the autobahn, the stability of those vehicles is quite good and so are the brakes (And associated brake dust lol). They're essentially overengineered for our roads in my mind. Sure the Prius is capable but I'd be more comfortable with the wider 17" wheels than the 15" wheels if I had to drive that those speeds.

    I might be eating my Sunday hat but I would guess a Gen 4 Prius w/ 17" wheels will run with a Porsche 924. (My point is that a modern car is much more capable than people realise... also, it's what we called sports cars back in 80s so those who owned cars in the 70s, 80s or early 90s and remember those poorer handling "middle class" cars will be pleasantly surprised how well modern pedestrian cars perform)
     
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  20. goldfinger

    goldfinger Active Member

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    I know what you mean. The gen 4 handles well under normal to slightly pushing it, but falls apart on you under max braking. It gets very floaty feeling when the abs is kicking hard. I have Toyo oem tires still. You just have to drive through it. I think the car deserves better tires.
     
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