Loud grinding brake sound before applying brake

It kinda sounds like a warn brake pad indicator. But why would your pads be worn?

 

Pebble or piece of wood stuck between the pad and rotor, in a safe area drive quickly in reverse and apply the brakes several times after going to a self serve high pressure car wash and cleaning things out.

 

Hello,

Wonder whether the suggestion about reversing and braking helped, as having the exact same issue, been with it for a long time, and driving me crazy!
It is so loud, that cannot have the windows open, and causes pedestrians to look.

 

Is it a squealing noise or more a grinding noise?

What mileage or usage do you give the car?

Are you heavy or light on the brakes? If the latter then I think it could just be rust or grazing on the brake discs getting worn off when you brake?

The Prius brakes don't get used much compared to other cars (due to regen braking) and with light use can rust over more quickly.

 

Hello GrumpyCabbie,

It is a squealing noise, which happens more at low speed, in tune with wheels turning, but sometimes at high speed. Very bad when crawling along in traffic.
The mileage is about 40000, mostly long runs.
Squeal does not usually start when cold, but after running for a while, and usually starts when brakes have just been applied.
Braking stops the noise, until I start moving again.
I have tried the Neutral braking, which seems to stop it for a short while, but soon starts again.
I'm very light on the brakes, using brake mode a lot.
Sounds like you think it is braking dust/glazing of the discs, wonder if you can comment.
Thanks,
Stephen.

 

Sounds like a case of taxi brakes to me. If the pads aren't worn (which they shouldn't be if you do long runs) and you don't have a sticking caliper, then the brakes could do with a right good clean.

The dealers should do this at service time but if you take it to an independent or a sloppy dealers, they might miss this!?!?!

Still baffling me though as I'm at 31k miles now with heavy start stop town driving and my brakes are quiet and have plenty of life left.

 

Thanks.
How would I confirm a sticking caliper pls?

 

Was this problem ever resolved?

 

Hello,

The stuck caliper theory meant I experimented, and have found that forcing the brake pedal further than I usually pressed, made the noise stop, so I guess that as I was so light on the brakes, that the caliper was getting stuck since it did not get exercised.

It irritates me that Toyota or my service centre did not resolve this and it took helpful comments from forum users to solve. Thanks to those who contributed.

When the car is next in for a service, I will get the calipers looked at and lubricated.

Regards,

 

Hello,
A further update.
Took the car in for a service by a different garage that originally said the problem was rusted rotors and wanted £500 to change them - I declined.
The problem was that the brake pads were not correctly seated in both fronts, maybe because the previous garage that changed them might have put them in incorrectly.
The garage re-greased and all has been fine since, so the problem is solved, hopefully, not to re-appear later.

 

Been there.

That grinding sound happens after it's rained. But just to be sure you should get to 30-40mph put the car in neutral and slam on the brakes. It will clean them. Between that trick and dry weather, the grinding noise should go away.

 

why did you have brake pads changed???
the prius usually doesnt need this until 60k 80k 100k miles...
if you had mentioned that in the original post it would have been easy to diagnose.
basically the pads were either not installed correctly, and /or pistons pads pins slides not lubed adequately.

the rotors/pads will not glaze on a prius, theres never enough heat to glaze them. the problem is from lack of use, rust grime corrosion build up, doesnt get properly polished off from good brake heating.
in fact, the prius brakes probably never get properly bedded/broken in.
during normal braking the prius brakes only engage at speeds below 5 mph. or in cases of hard/emergency stopping.
teh regen motor does all the braking normally to recharge teh battery.

 

do the 40 mph, slip into Neutral, then steadily/firmly brake to 5 mph , accelerate to 60 mph, into N again, brake again.
note dont slip it into B
you want to be in "N"
when in neutral the regen system wont engage, and you will truly be using ONLY the brakes to slow and stop.
i would do several cycles of this to clean off your rusty rotors, inspect them before and after. the heat and pressure of true braking will clean them.

then repeat every 2 weeks or as needed in rainy / wet climates.

hopefully your rotors are not too rusted.

 

Hello,

I have looked back and don't find that they were changed during any service, so it is a good question, why did they get out of position. Maybe the lub of the slides is the answer.
Annoying as easily solved and sorry for the duff info in the previous post.

I am usually very light on the brakes, using the brake lever often, and sometimes not touching the brakes, so the stuck caliper theory seems likely since the brakes were so little exercised.

Glad it's solved, and thanks for the information on this forum.

Stephen.

 

Is there a chance you have a wheel bearing going? Hal

 

Hello,

Since the garage have done the work on re-seating the brakes, the problem has gone, so they have definetely found the cause, and presumably this means the wheel bearings are ok.

Thanks,
Stephen.