So i know that when you open the driver side door after the car has been sitting awhile (2010 Prius), it makes a whirring noise and that's the brake system pressurizing before you start the car. But this whirring continues as i drive the car at lower speeds within 5-10 minutes of starting on my way to work. The first mile is pretty much down hill, only need the ICE for about 1/5 of that distance, and use regen braking all the way. When i come to a stop sign - there are 3 in that first mile - the whirring sound kicks in. I notice it most when i'm stopped, then slowly creep forward as the car ahead of me goes through the stop sign and it's my turn to stop, i'll hit the brakes for that last bit and hear the whirring. Is this normal after the has been started and driven for a short bit?
It isn't driving that makes the whirring, it's braking. Each time you press the brake pedal it uses some pressure from the brake system. Eventually this pressure is restored by the brake accumulator pump, which is that whirring you describe. The pump running every third time or so is normal. It should not run continuously. Tom
Thanks Tom, it doesn't run every time i brake that i recall, and it doesn't seem to do it after i've driven for a bit. If it runs every time, what does that mean?
If it runs continuously it means your brake system has a pressure leak. Running every time you brake could be nothing more than your braking habits. Tom
ahh, perhaps i misunderstood what i read, oops. I read that as: 'continuously meant that it happened every time i hit the brakes', instead of meaning 'running for the duration while the car is on, not just while pressing the brakes'. and no, it only happens when i press the brakes upon coming to a stop, not all the time. that's clearer for me now that i've had my coffee!
Your car isn't old enough yet, but it -can- run -every single time- you press the brakes. This indicates the pads are worn and the system has to move them farther, taking more volume (it's not pressure, it's volume that triggers the use of the system pressure - in other words, if your system only had to move 1 cc of fluid instead of 10 cc the pressure would drop much less and the pump would run less). Oh, and you're much too sensitive to the sounds the Prius makes. I recommend loud rock music with earbuds to remedy this.
yeah pretty sure the pads aren't worn. I better understand what's going now. and yes loud music helps!!
Disc brakes self adjust with an ingeniously simple system. They don't move further when they are worn. This will save me a bunch of typing Disc brake calipers
In 46years of driving cars with disc brakes I have never had them not work. Square o-rings are pretty reliable. If they don't work, your pedal will go right to the floor when the pads wear a bit. Edit: A little clarification. I was referring to the self adjusting feature of hydraulic disc brakes, not the entire disc brake system.
