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Discussion Starter · #1 ·
I read about this somewhere on this forum before but can't find it now. Can someone explain why this happens? Generally I reduce brake pressure a bit and it "catches" pretty quickly. I noticed it in particular today while descending a slow, steep hill in town. Decent sized frost heave presented itself and the regen stopped. I'm mainly curious why this happens.

TIA
 

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Frank06 said:
I read about this somewhere on this forum before but can't find it now. Can someone explain why this happens? Generally I reduce brake pressure a bit and it "catches" pretty quickly. I noticed it in particular today while descending a slow, steep hill in town. Decent sized frost heave presented itself and the regen stopped. I'm mainly curious why this happens.

TIA
I think it's a safety thing where the system prepares for an emergency stop with the friction brakes...reading the bump as a loss of control. I usually try to keep an eye out for bumps and take my foot off the brakes before the bump then reapply after.
 

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I'm second to Evan.
My bet is as follows...
- The ABS detected one or more wheel(s) slipped.
- Then, the vehicle went to a safety mode under control of friction brakes, no chance for regeneration.
- To exit this mode, try to push the accelerator pedal in a short period to tell the vehicle no more braking even if you are still going down hill. :)
- Now, you'll go back to a normal mode to see regeneration.

Good luck!
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Anyone notice that the friction brakes apply at least for a moment during the initial application of brakes? I have been hearing a slight, brief squeal just as I start applying brakes for a traffic stop when driving with the windows open. MFD still indicates regen though.

I thought it might be someone else, but the squeal seems to follow me around, and at moments when I apply brakes.

System doing a brake check?
 

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Discussion Starter · #5 ·
If the battery is low when coasting down a hill I will sometimes lightly ride the brake (just enough to activate the light and a bit more regen) and can hear a high-pitched noise. I always thought it was the controller.
 

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DanMan32 said:
I high pitched noise is the inverter doing the electrical conversions. What I hear is definitely a brief brake squeal.
Quite a while back someone mentioned the same squeal you are reffering to, I don't remember what came of it... try doing a search here or on PC?
 

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I am not concerned about it. I figure it is the brakes getting ready to activate, a "brake check" if you will. Just found it strange that I would hear a squeal as if the hydraulics were being applied when it should be regenerative.
 

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Brake Squeal

Years ago, I used to commute across town almost entirely on the freeway. Light brake usage caused glazing on the brake pads and discs, which resulted in a high pitched squeal during braking.

After coming across an article on how brake dust can form a glass-like glaze burned onto brake surfaces, I tried the fix that was suggested. Find a lightly travelled road where you can run your car up to 60-70 mph, and then hit the brakes hard until you come to a complete stop. Then, repeat about three or four times to heat up the brakes. This heat will break the glaze and the squeal should go away (or at least be significantly reduced).

The only other alternative is to get a brake job, where they turn the discs and drums, and replace the pads and shoes.

I suspect that since Prius's use regenerative braking, they also suffer from glazing.

Just a suggest -- might be worth a try...
 

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Brakes

DanMan

I agree with Phoenix in that the glaze needs to be broken by having the drums and rotors turned at a shop or dealer. If the rear brake shoes and front pads still have enough material on them they do not need to be replaced but the shop or dealer can use sandpaper to brake the glaze.

Once the rotors and drums are turned and the glaze is broken any squeek or squeal you have will go away...guaranteed.

I have to disagree with running the car at a high speed and hitting the brakes to break the glaze however. Heat causes glazing. In my opinion, this would make it worse not better.
 
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