Have you experienced the "grabby" brakes?

Hello Blindguy,

What's concerning to me, is this something caused by the Owner/Operator somehow?? I see such a high percentage of people who have experienced this, yet I have NOT experienced it. 3K miles now, and if it's something in braking system, you would have thought, even though "intermittent" I myself would have experienced this????

I have not experienced the "accerleration issue" as well.

I actually anticipate these to happen based upon posts etc.

Since I have not (YET), I wonder if it's some specific operation that causes it?? I wish we could get some real detailed posts with several questions to maybe narrow it down. Not sure how to do that yet...

I wonder if it's chain of events (be it ever so quick) that causes this? The Brake Actuator pump, possibly and starting and going into reverse or drive to quick was one assumption I had???

It's mid boggling is all....But I thought I would just share my concerns and comments...

Mystery still???

 

I think the car would not speed up if it hydroplanes, what would happen is the front wheels might spin and it would sound as if it were speeding up. The Gen3 Prius CC will shut off if the windshield wipers are put on high speed for more than about 4 or 5 seconds. It still works fine if they are in intermittent or low speed. The LKA will shut down if they are in low or high speed but still works if they are in intermittent.

:focus: I have not experienced the grabby brake in reverse issue. I have experienced the "heart in your throat" momentary loss/decrease in braking at low speed on rough roads a couple of times and I really don't like it. This is a "feature" we could do without Toyota.

 

I've experienced "grabby" brakes on reverse, but I think I've isolated the cause. If you put the car in reverse too soon after starting, i.e. while the dash computer is still booting and saying "Welcome to Prius", you will have grabby brakes. If you wait a few extra seconds to make sure the car is fully on after starting before putting it in reverse, you'll never have the grabby brake problem. I'm guessing something involved with the intelligent brake assist isn't fully functional in the moments after hitting the start button. Maybe the same effect happens when putting it in drive to soon after starting as well.. I don't do that very often, so I haven't confirmed this.

 

This is entirely consistent with the two instances I experienced the problem.

 

It's caused by stuff on the brake discs, due to the car sitting for a while, such as in the transit from the factory to dealer. So I'll say that unless your car sits outside for a couple of weeks in damp weather, you probably never will experience it. It's not a big deal... annoying, but not dangerous.

[EDIT: Some people evidently experience it at other times, and the theory, above, that it has to do with putting the car into gear quickly, may have some merit, but I'm not so sure. I don't think the Prius III has brake assist -- or whatever they call that feature where the car is held on a hill when you push the brake extra hard -- so maybe that's a factor. I still think the majority of brake grab is new cars and rusty/contaminated discs. That's certainly the feel that I had on mine.]

Neither have I and I'm up to 5500 miles. So I'm not sure if it's very picky to induce, whether it only applies to particular cars/models (I have one of the first Prius III's in the DC area), a particular driving style, or what. Maybe it's people who are new to ABS, or maybe Toyota's ABS is different, or maybe I'm a more conservative driver now that I drive a Prius, or ...

I really don't have "let me just drive around" time, but sometime I'm going to have to go out to try to provoke it.

Everything I've read about the "acceleration" issue is that it mainly happens on hard braking on a rippled/bumpy road surface, which causes ABS to engage and Regen Braking to disengage.

In terms of the brake grab, that also happens at low (driveway/parking lot) speeds, within the first week or two of buying the car or after leaving it in the driveway for a while in humid weather.

The brake grabbing is a non-issue. I've had it happen on other cars in the past when they've sat outside for a while. It's annoying, but would be hard to imagine it being in any way dangerous. And it will go away by itself as you brake, or you can quick-fix it by driving at speed, shifting into Neutral (to force it to not use Regen braking), and braking to a stop. [EDIT: Again, assuming its the rusty-disc-induced brake grab. If there's a defect in the hill-holding function...]

 

INteresting. I'd say that it has to do with the hill-holding feature and a quick start, though. I have a Prius III, which I don't think has hill-holding, and I definitely put the car into gear quickly often and never experience brake grab. In fact, at times, I'll hold the shifter in N while the car's booting, so that I hear the doors lock the instant it's Ready. I think I also do this with D sometimes, though usually, my little startup ritual takes long enough that I'm not shifting until it's all Ready.

 

I have experience braking in reverse problem once which I have to step really hard and deep into the brake to stop the car (feel like no power brake) soon after I purchase the car. Today, 3000 miles later, I have encounter the grabby brake problem going forward.
In both case, I did not leave my seat after I turn off the power. After I started the car by pushing the start button, shift to drive to go forward to the gas pump to get gas, I step on the brake lightly but I am getting a big jerk as if I am doing a panick stop. I let go of the brake and reapply and the same reaction. In both cases, I have to put the car in Park and to drive or reverse again to resolve this problem.

 

I'm not sure what others are experiencing when they say "grabby brakes" but what you describe above, is what I mean. You barely tap on the break and if feels like your head is about to go through the windshield or when reversing, head slams against the headrest. I've eliminated this issue by waiting a few extra seconds after hitting start before putting it in gear. Just let the car boot up fully first, then put in gear, and the breaks will work normally. I'm not sure why they are so sensitive when putting in gear too soon. But like I said before, it feels like what cars do when they engage IBS, 'intelligent brake assist', by making the breaks more sensitive when it detects a panic situation, ie slaming on the breaks or perhaps with the Prius V, it may be a feature of the pre-collision actions. It has nothing to do with Hill Assist. That simply holds the brakes on a hill until you hit the accelerator and you must first activate that by pushing hard on the break on a hill. Hill Assist does not make the breaks more sensitive.

 

I can resolve it by releasing my foot off the brake completely and re-applying it.

 

Has anybody found a repeatable way to get into this "grabby-brake" mode?

My experience also has unexpected "power" being applied to the wheels instead of the low-power "creep" that one normally gets with no-accelerator operation.

 

I've noticed it a couple of times...always in reverse, and it seems, only when wet.

 

Yes, I experienced the increased acceleration (in reverse, downhill) and grabbing brakes. Only once so far in the 300 miles I've had the car. It went away after going forward and selecting reverse again. It appeared to be a software problem, a different control mode incorrectly selected. Temperatures were moderate, weather was dry, and the car had been parked for only about an hour while having lunch. I would be more concerned about the extra acceleration than the grabbing brakes, from a safety viewpoint.

 

I don't know if this is a similar problem but I was taking my kid to school yesterday and the car was pretty wet from being parked outside over night. Anyway I was about 2 miles form home and had been driving for 8 mins.

The car in front of me slammed on the brakes and I hit the brakes as well. The rear brakes felt like they locked up literally...no anti-lock pulsing just a lock and a slide that scared the s*** our of me.

I am taking it to the dealer for evaluation...my car has 500 miles on it.