severe noise when braking hard

Hi. Most braking is from using the variable regeneration to charge the HV battery, but there are hydraulic brakes which (not quite seamlessly) are used for fierce braking and just before you come to a stop, etc. The steel rotors are not used nearly as much on the Prius as with a regular car and the rotors tend to corrode from damp to produce a rusty skin. This wears of after a good run and a few firmer braking events and is fairly normal, but if you are only traveling a few miles each trip, it could seem like a permanent feature. I hope this helps, but come back if there's more to be said.

 

welcome!
agree with rco ^^^, they might have adjusted the brake pad shims, clips or something, hard to say.

try going 25-30mph on a quiet road, put the car in neutral, press the brakes gently and listen for sounds.

when in neutral, it's all brake pads and no regeneration. if it is rust on the rotors, it will soon wear off and the noise will go away.

if the noise remains, it's time to take another one for a test drive with the service advisor and compare.
all the best!

 

With excessive brake pad wear your hydraulic brake resevoir should have dropped. Have you checked the level?
If it is still full I would agree with earlier replies.

 

I would have them looked at, or DIY, just a visual inspection with the wheels off, for starters. 8000 miles since it sat on the lot? It should not have rusty rotors still, and you would be hearing them with every application of the brakes.

The one thing I can think of, when you say step on the brakes hard, do you mean really hard? In emergency braking (stand on the brake, panic stop), the Anti-Lock Braking will activate, and you should hear a loudish, pulsating noise.

 

my rotors rust up every night in my garage, unless humidity is really low, which is about a dozen days a year.

 

Especially if I've washed the car, or just driven in heavy rain, if it subsequently sits 2~3 days, with the next drive the brakes will be a little noisy, for a block or two, but no more than that.

 

Back when I bought my first Prius in 2008 and started hanging around PriusChat, this was already a well-discussed issue, along with the solution. By now, it's just second nature—if I get in the car and it's been sitting in damp, I pretty much expect the brakes to be grungy, and if they are, I shift to N for my first 2 or 3 stops on the way out of the neighborhood, and they're all silky again.

Now, six months of damp might take more than 2 or 3 stops to erase ... that would be a "see how it goes" situation. If some rotor rust gets well-enough established, it starts reshaping the pads in its own image instead of getting scrubbed off, and if that starts happening, an intervention is needed. But a bunch of stops in neutral is the first thing worth a try.

-Chap

 

The worst case I had was after I misassembled the rear brakes, leading to uneven brake application. About 50% of the inner face of the rotors was quite rusty. I removed and cleaned them with steel wool, best I could, and reassembled correctly. But still they sounded like shite at first, with every brake application, in Drive. Within a day or two it was better. Within a week it was just discernable still. By a month it was completely back to normal.

If I'm hearing a bit of noise, say after the above carwash or heavy rain scenario, within a block or two the noise is gone, without the need for any special tactics, say braking in Neutral. In short, just driving normally, it clears up quite fast.

 

I've had damp nights making the brakes grungy enough that they would stay that way through my entire morning commute at least (and be not only noisy, but grabby), but the brake-in-N technique has always cleared them off for me within two or three stops. I can't take credit for the technique; I was taught it myself by the then-elders of PriusChat eight years ago.

There is at least one thread on here from an unfortunate owner who did not know the technique, and whose brakes did not always clear up on their own without it, and who repeatedly went in to a dealer about the recurring noise and grabbiness, and was repeatedly fleeced out of $900 each time.

Knowledge is power....

-Chap

 

I remember my 2008 made those noises with the brakes all the time but the new one doesn't. I wonder if they are using a different rotor.
Not all cars are as bad as a Gen 2 Prius.

 

I have the same issue in my 16 prius, I heard noise coming from left side when braking...
I cleaned rotor(it was perfect). But still noise not gone. Yesterday I got to know it is not brake or rotor problem, because while driving down from a hill with speed 30 mph, I changed transmission to (B), then I heard the noise again.... so the noise coming when deacceleraction whether I'm using brake or transmission(B)... now I have to check Axle and bearings,,, otherwise, sound coming from motors generators.

SM-G955F ?

 

I find braking whilst reversing off my drive cleans mine, as regen doesn't work in reverse.

 

That's interesting ... I can't think of any technical reason for regen to be disabled in reverse (other than that it generally doesn't do much below 7 mph or so, and people aren't usually speed demons in reverse).

Anybody else observed one way or the other?

 

If my brake rotors are a bit rusty, say from sitting a few days after a wash, I can hear them, with every brake application, for the first block or two. My take: there's pretty much always some percent of friction braking going on.

 

"

 

That's a description from the manual about driving in reverse, but the question was about braking in reverse.

May sound like hairsplitting, but it affects the roles of the MGs. Even in forward driving, in regen braking the electrical generation is done by MG2. MG2 can easily generate in either direction of rotation. The manual passage about MG1 is a bit of a red herring for this particular question.

 

Hmmm - yes, I see what you mean, sorry, don't know.