Braking problem

[eglmainz]

** Update 05/FEB/2010 As of now, we are hearing that Toyota did make some adjustments Prius Built after December 2009. As of now, there is not yet a formal recall for this, but I suspect that they will in short order. As of now, I have 22,500 miles of my 2010 Prius V, and this 'floating feeling' still occurs to me almost daily, but I have gotten used to it, and have never thought the brakes will not work. Just keep the pressure on your pedal the same, and you should be fine. **

I am not sure if any others here have experienced it yet, but I have at least 4 times in the last few weeks, and it is a bit scary...

I'll be slowing down, and maybe needing to brake a little harder than I like, and if you go over a large bump in the road (large= more than 1 inch high, like a misaligned concrete crack or something close to that), it feels as though the car almost speeds up for a second before braking.

Each time, it leaves a small pit in my stomach. Luckily, I have never yet had it happen for more than a second, but it seems as though the ABS is releasing for a second before it may kick in as it feels the wheels bounce a bit?

If it matters, I am driving a Prius V.

[Husker4theSpurs]

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.

[eglmainz]

Originally Posted by Husker4theSpurs

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.

I wondered that as well, but the last two times, I was down to under 10 miles per hour when it occurred, and while I know that Chicago has some pretty bad streets, I do not think that this fully explains it. I am a bit concerned by it. I have had ABS on my cars for the last 10 + years, so it is not a matter of a normal ABS feeling. It was much different that that. Each time, it actually scared me a bit.

[john1701a]

Originally Posted by eglmainz

Each time, it leaves a small pit in my stomach.

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.
.

[syncmacd]

Originally Posted by eglmainz

I am not sure if any others here have experienced it yet, but I have at least 4 times in the last few weeks, and it is a bit scary...

I'll be slowing down, and maybe needing to brake a little harder than I like, and if you go over a large bump in the road (large= more than 1 inch high, like a misaligned concrete crack or something close to that), it feels as though the car almost speeds up for a second before braking.

Each time, it leaves a small pit in my stomach. Luckily, I have never yet had it happen for more than a second, but it seems as though the ABS is releasing for a second before it may kick in as it feels the wheels bounce a bit?

If it matters, I am driving a Prius V.

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.

[qbee42]

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

[yardman 49]

Originally Posted by qbee42

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

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.

[greylar]

Originally Posted by eglmainz

I wondered that as well, but the last two times, I was down to under 10 miles per hour when it occurred, and while I know that Chicago has some pretty bad streets, I do not think that this fully explains it. I am a bit concerned by it. I have had ABS on my cars for the last 10 + years, so it is not a matter of a normal ABS feeling. It was much different that that. Each time, it actually scared me a bit.

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

[wyounger]

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.

[Nanster]

Originally Posted by wyounger

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.

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.