brake surge again!

Near work there's a spot going downhill, just before a curve. There are some filled-in potholes, resulting in a bit rougher, somewhat looser surface in that area. The rough spot is maybe six feed wide and a dozen feet long.

The spot is just past the point where one starts braking in order to (a) take the curve and (b) stop at the stoplight at the bottom of the hill. The braking is nice and steady, but about half the time, when the car hits the rough spot, the car does the Prius Regen Switch and the braking force decreases until the mechanical pads kick in. The first time it happened it was a "Whoops!" moment; since then, it feels normal.

Yeah, my 2010 Gen III has the recall fix.

KBeck

 

Do the 2010's do this even after the software update? I felt it in rental Prii when the 3rd Gen first came out. Kind of a weird feeling but I stopped the car whenever I needed to stop.

Mike

 

Basically, yeah. Just so we're clear: My understanding is that there is still braking going on during the switch from regen to mechanical braking, it just becomes less during the switch time. So, your butt feels like you sped up (change of rate of deceleration) briefly, then the mechanical brakes kick in. The software change shortens up the time from the beginning of all the fun to when the mechanical brakes are working.

So, if you're traveling at 20 mph and regen braking (i.e., the brake pedal isn't mashed hard), and your planned stop point is one foot behind the bumper of the stopped car in front of you, you hit that slippery spot, the cars electronics do a fast song-and-dance and switch to mechanical; and, if you didn't change the down pressure on the brake in all of this, you'd likely stop a foot past the rear bumper of the car in front of you. But you'll feel the weirdness and stab the brake and stop in time, which is unsettling, which is why people run around in circles here at Prius Chat and bitch about it.

On the other hand: Below 13-10 mph, the car will automagically be in pure mechanical mode anyway, so panicked stops in the last ten feet won't happen, unless you hit black ice or something, in which case, no matter what kind of car you'd be in, you'd be in trouble anyway. So the design of the car with the switchover points means that while one will be unsettled by the funny business in the brakes, it typically, given adequate human reaction times, won't be an issue in stopping. Unless the driver is truly asleep at the wheel.

Finally, I appreciate B. Wilson's research into figuring out if there was a second somewhat buggy thing going on. One doesn't find if one doesn't look, so putting an accelerometer into a car that acts weird is all to the good.

KBeck.

 

For reference.

 

This pretty much matches my understanding and feeling about what is happening. It seems to occur only under light to moderate braking where plenty of stopping margin is available by escalating to hard braking.

If it happened under hard braking (which regen is incapable of providing) where little stopping margin is available, or prevented the driver from escalating to hard braking, then my concern level would rise very sharply.

 

This happened for me couple days back. It was not the usual switch from regenerative to normal braking.
The road was little wet and I hit a bump and the car didn't start breaking for like 2 seconds and there was some strange noise from brakes when it happened.
Kinda scary and thx god there was no cars in front of me.

 

Make sure your recall has been carried out. Mine used to be like that but stopped when the recall was done last year. Since then the brakes have more 'bite'.

 

The first time I experienced the issue was full 3 years after buying the car. It was purchased after the recall.
Now, I make sure to avoid braking on uneven surfaces as it's not healthy for brakes and suspension (i was told long time ago). But this one time I had no such luxury and I almost rear ended the car in front of me. I was unsettling a bit. The worse part was the road was very dry with good traction and there was no good reasons for brakes to do that silly thing.

Why would there be a delay between regen and hydraulic in the first place? When one brakes to a stop this transition happens all the time at ~7MPH and it's very seamless.

 

Once the LATEST brake recall has been instigated the problem goes. The first recall helped but didn't totally or fully eradicate the issue. The last one did - completely (at least by my experience).

Check your car has the full recalls done on it. Don't assume previous owners got it carried out.

 

Are you talking about the leaking brake pressure accumulators bellows recall? I don't qualify for that.

 

No, though I've had that done as well. I'm meaning the software update recall on the brakes to stop that floating feeling when braking in certain circumstances - ie, what you're describing.

 

I think you are talking about the 2010 recall. My car was made after the change. I bought it at the end of 2010.