Braking problem

Re: Floating feeling when braking

I have had that happen as well ... also happened in my Gen 2 ... in the Gen 2, the VSC would be kicking on as well (or stability control ... whatever). Had to be a pretty big hole or crack ... I think it's the car thinking that wheel is spinning b/c it has lost contact with the concrete for a short while.

 

Re: Floating feeling when braking

It isn't as sensitive in the 2010 as the Iconic model. You have to hit a fairly decent size bump while braking hard, so the behavior is predictable... and as you stated, quite brief. Nonetheless, it is there.

Funny thing is, a similar thing happens on traditional vehicles... only you've been desensitized to it. Drop the gas pedal, that hard thunk of abrupt downshifting will scare the crap out of someone who has never experienced an automatic transmission being strained.
.

 

Re: Floating feeling when braking

I have had that happen to me, when I was going 70 mph and then traffic came to a stop in front of me (fancy that happening in California). I hit the brakes and then must have hit a crack as the car felt like it rose for a moment. I think it's the price we pay for driving a car that weighs so little; my wife's SUV might not have even have felt the bump.

 

Re: Floating feeling when braking

It is essentially traction control kicking in. Regenerative braking works with only the front wheels (the powered wheels). When you hit a bump, traction is reduced. The braking system notices the loss of traction, cancels regenerative braking, and switches to friction braking. This all happens in a heart beat, but it feels longer when you aren't expecting it. Just keep braking and all will be fine.

Tom

 

Re: Floating feeling when braking

Quite often I've rented Ford products for work. Some of their bigger models (Mercury Marquis, etc) will also have their ABS go beserk (overcompensate) when slowing while simulaneously hitting a bump. Makes your heart skip a beat, because you think "help, I'm not going to stop in time!!!".

There was a particular stretch of road that I drove often, where I had to come over a slight rise on an overpass, then make a left turn onto the freeway. This phenomenon would happen to me every time when driving those big Fords on this route.

Interesting, because going over that same stretch of road with GM's and other manufacturer's models did produce the same problem.

Tom is right-on with his explanation of why this happens on the Prius.

 

Re: Floating feeling when braking

This is super normal and it is just keeping your wheels from locking up. Just jab the brake a little harder. Definitely an oh s** moment for a fraction of a sec tho, you will get used to it.

G

 

Re: Floating feeling when braking

I agree with the diagnosis and had reached this conclusion myself independently. I had a '94 Ford Taurus with ABS that was worse about this than my '07 Prius. Individual tires will briefly (a fraction of a second) lose contact with the road over certain types of bumps in all kinds of cars; if you're braking when this happens, the wheel stops rotating almost instantly when it loses contact with the road because the brake is then only stopping the rotating inertia of the wheel, not working against the kinetic energy of a whole moving car. Vehicles with sensitive ABS systems will detect the wheel stopping too quickly as a "slip" event just as if you hit a patch of ice and start to react as if more of the same is to come. I've had ABS in my cars for many years now, and having gotten used to the feeling, I can say that it only scared me in that Taurus. It backed off the brakes so strongly for so long after a tiny-slip event that I truly did almost hit things a number of times while it slowly decided that it was OK to allow me to brake as much as I wanted.

 

Re: Floating feeling when braking

The bolding is mine. I just bought a used 2005 a month ago, and I have had this happen a half dozen times already. So having breaks that slip and cause you (almost) hit things is NORMAL on this car? That does not instill a lot of confidence! I'm starting to become afraid to drive it already.

 

Re: Floating feeling when braking

If this is your first ABS equipped car, don't release pedal pressure if you feel the pedal pulsating, keep constant or increased pressure to stop where you want. In my own experience with ABS on a dozen or so cars since the late 80's I've only felt the ABS kick in during snow and ice conditions, but I'm not driving at 9/10ths on dry roads. I can't relate my own experience to the drivers who experience ABS action frequently, but no matter the surface, keep the pressure on steady.

 

Re: Floating feeling when braking

omg i thought it was just me w/ this problem it happened to me twice thinking if there would be a car close in front of me big accident will happen hope toyota will fix this!

 

Re: Floating feeling when braking

I've experienced this as well. I'd be braking and going over some small hole when it occurs, but it doesn't scare me. The only scary floating feelings have been on the way back from Taco Bell...

 

Re: Floating feeling when braking

Hello Nanster:

You seem to have misunderstood wyounger. He was not refering to the Prius, but to his Ford Taurus when he made the following statement (bolding is mine):

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I've driven my Prius for over 5000 miles now, and have never come close to hitting something because of the ABS brakes. If you read my previous post in this thread, and that of others, you will see that this type of behavior is common to many cars that have ABS. Granted, it is more noticeable in some models than others.

I try to look on the positive side: the regenerative brakes work wonderfully. Just a light touch is need to begin smoothly slowing the car down at a in a very controlled rate, with very little pressure on the pedal. But when you really need to stop suddenly, stomping on the pedal will bring the car to a stop very quickly. After you learn how the brakes behave, you should become comfortable with their operation and no longer be startled by the ABS system.

 

Has anyone, with a 2010-V ATP, experienced a forward lunge while driving and braking when navigating over a bumpy road or pot hole in the economy mode? This happens every time I brake while on an uneven surface, not just occasionally. My first thought was that it may be related to the anti lock braking system, however, I am not braking hard when this happens.

This is a very scary experience, fortunately for me this has occurred when there have been no other vehicles, bikes or pedestrians in front of me. The car lunges about two to three feet and regains composure when it hits a smooth or even surface.

Any suggestions or should I schedule a service appointment today?

 

there's anotehr thread abotu this recently, did you try a search?

 

This is caused by a loss of traction during regenerative braking. The issue isn't unique to the Gen III. A quick search of this site will show that the issue is well documented and understood. Whether it is a problem or merely a begin artifact remains a topic of debate.

In short, this is what happens: During regenerative braking, only the front wheels are slowing the car. Hitting a bump causes the front wheels to lose their grip, causing the braking system to stop regeneration and switch to friction brakes.

The car does not lunge forward or accelerate during one of these events. Braking force momentarily drops, which causes a sensation of acceleration. In reality acceleration drops, but sense braking acceleration is in the negative direction, it feels like forward acceleration. The car does not gain speed or jump forward.

Tom

 

Tom's explanation seems to be the accepted theory, and I have no reason to disagree. I also believe it is benign, though I'll admit it really gave me a scare the first time it happened to me.

It happened on my 2007, and it happens on my 2010 Prius V w/ATP.

The times it is really noticeable are those times when it is scariest: You are coming to a stop or slowing due to traffic congestion, so you know you must avoid something ahead of you; you are braking steadily and fairly heavily, relying on the front brakes (which are using the regen system); you hit a bump, the brake load shifts to the rear brakes (and you do lose, momentarily) the full braking power; the feel is that you are accelerating, despite the fact you are braking; a fraction of a second later the brakes "work" again, and your heart starts pumping normally.

I freely confess that to this day it will put a jolt into me, even though I am fully aware there has been no system failure.

 

I did search first and read several posts about braking before I posted this, perhaps I was using the wrong criteria.