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Old 18th September 2014, 12:57   #61
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Default Re: Noise from the Brakes

My new I20 (300 kms on the ODO) sometimes makes a 'swoosh' sound when I press the brakes a little harder than normal. It seems like air being pushed out - but that could be a huge worry for a new car right? Never noticed any brake fluid leakage or anything amiss on the control panel. Help
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Old 18th September 2014, 13:21   #62
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Default Re: Noise from the Brakes

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My new I20 (300 kms on the ODO) sometimes makes a 'swoosh' sound when I press the brakes a little harder than normal. It seems like air being pushed out - but that could be a huge worry for a new car right? Never noticed any brake fluid leakage or anything amiss on the control panel. Help
That is the brake booster doing its job. Should be hardly audible at driving speeds, easily noticeable on a standing car. Nothing to worry about.
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Old 18th September 2014, 13:25   #63
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Default Re: Noise from the Brakes

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That is the brake booster doing its job. Should be hardly audible at driving speeds, easily noticeable on a standing car. Nothing to worry about.
I am planning to take the car to Ooty (from Bangalore) on the Oct 1st long weekend - was really worried about driving with iffy brakes on the ghats.
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Old 18th September 2014, 13:36   #64
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Default Re: Noise from the Brakes

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Originally Posted by smukherjee View Post
My new I20 (300 kms on the ODO) sometimes makes a 'swoosh' sound when I press the brakes a little harder than normal. It seems like air being pushed out - but that could be a huge worry for a new car right? Never noticed any brake fluid leakage or anything amiss on the control panel. Help

First thing, i20 does not have Air brakes. So there is no air to be pushed out.

Second thing, are you getting this swooosh sound if you decelerate rapidly from high speed(Above 50 kmph)? Not slamming on the brake kind but smooth progressive increase in pedal pressure at high speeds. If yes, this is normal and i have experienced this in the car
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Old 18th September 2014, 14:07   #65
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Quote:
Originally Posted by smukherjee View Post
My new I20 (300 kms on the ODO) sometimes makes a 'swoosh' sound when I press the brakes a little harder than normal. It seems like air being pushed out - but that could be a huge worry for a new car right? Never noticed any brake fluid leakage or anything amiss on the control panel. Help
Not to worry. That sound comes from my i20 aswell (4 mnths old).
Since you've also noticed this, I'll ask my service advisor about this when I'll visit HASS sometime next week. Im guessing it will be a normal thing. Will keep you posted.
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Old 18th September 2014, 14:18   #66
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Do you get the swoosh sound only when you are pressing the pedal? So once you keep the pedal down and are braking it goes away? So directly and only proportional to the brake pedal movement?

If so, it could be just a bit of mechanical sound coming from the master cilinder as you move the plunger which is attached to the brake pedal via some linkages. The plunger displaces the hydraulic fluid and the seals ensure a tight fit. Plunger movement inside the master cilinder and displacement of hydraulic liquid might lead to these swoosh sounds. Also, there might be some rubber bellows at back of the master cilinder where the plunger goes in. When pushing/releasing the brake pedal these bellows expand/crimp. Sometimes you hear a bit of air being sucked in or blown out. The bellow is only to prevent dirt built up on and near the plunger and seals.

Any of the above, nothing to worry about.

Jeroen
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Old 18th September 2014, 14:48   #67
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Default Re: Noise from the Brakes

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Originally Posted by sagarpadaki View Post
First thing, i20 does not have Air brakes. So there is no air to be pushed out.
Sagar, all modern cars come with brake boosters which do suck in air to replace the vacuum in the booster. This is vacuum assistance. This helps cut the effort in pressing brake pedal by the driver.
So, the sound is not of being air 'pushed out'. It is in fact the sound of air getting sucked in.

Regards,
Saket
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Old 18th September 2014, 15:36   #68
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Default Re: Noise from the Brakes

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Originally Posted by saket77 View Post
So, the sound is not of being air 'pushed out'. It is in fact the sound of air getting sucked in.
If its the booster, it's both. One side is vacuum, the other side is open to vent to the air. So depending on whether you step on the brake pedal or release the brake pedal, air gets sucked in, or air gets expelled respectively.

Now, open up your hood, leave the engine and ignition of and push on the brake pedal a few times. then try with the engine of. The difference being having vacuum or not having vacuum and depleting the vacuum with a few pedal stroke as the engine or ignition is switched off.

Is the sound really coming from the booster?

Could be, but it might be other causes as per my earlier post

Jeroen
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Old 19th September 2014, 11:49   #69
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Default Re: Noise from the Brakes

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Originally Posted by Jeroen View Post
If its the booster, it's both. One side is vacuum, the other side is open to vent to the air. So depending on whether you step on the brake pedal or release the brake pedal, air gets sucked in, or air gets expelled respectively.
Jeroen, I did not get the quoted part of your post. My understanding is that one end of the brake booster is connected to engine vacuum which keeps creating a vacuum in the booster while the engine is running. The other end draws in air when the pedal is pressed which replaces the vacuum. This helps make the pedal lighter in operation. I believe there is no air pushed out from any end as the air that gets from one end is cleared by the vacuum created at the engine end.

Regards,
Saket
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Old 19th September 2014, 14:05   #70
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Default Re: Noise from the Brakes

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Originally Posted by saket77 View Post
Jeroen, I did not get the quoted part of your post. My understanding is that one end of the brake booster is connected to engine vacuum which keeps creating a vacuum in the booster while the engine is running. The other end draws in air when the pedal is pressed which replaces the vacuum. This helps make the pedal lighter in operation. I believe there is no air pushed out from any end as the air that gets from one end is cleared by the vacuum created at the engine end.
Hi,

there are all sort of brake boosters out there, but lets start with the basic most simple form of a car brake booster. I explain and I also found quite a nice article with some good pictures hopefully explaining it in some more detail.

A brake boost is essentially a cilinder with a flexible membrane in the middle. One side of the membrane is attached towards the brake pedal, the other side toward the plunger. By creating pressure differential over the membrame it assist the force from the brake pedal.

So it needs a pressure differential, otherwise it would not work. On the side of the plunger it is connected, via a check valve to the engine intake manifold or vacuumpump (e.g. on a diesel engine). So on one side of the membrame a vacuum is created and maintained by either the engine intake vacuum or the vacuum pump. The other side of the membrame is open to the atmosphere.

When you push the brake pedal you push the plunger in. Its assisted by the vacuum on the one side of the membrame. On the other side of the membrame, as this is open to the atmoshere air actually is "sucked" in if you like because of the displacement of membrame. Conversely, when you let go of the brake the membrame returns to it's original position and that menas the air that was 'sucked in" is expelled again.

So the vacuum is not replaced as you said/thought, it's maintained all the time. The vacuum side is completley seperated from the other side which is open to the air. If the membrame develops a little tear you loosed the vacuum and that results in the booster not working properly and you feel that in having to press the brake pedel more to get the same braking response.

Have a look at this:

http://auto.howstuffworks.com/auto-p...wer-brake1.htm

For those of us are more visually orientated here is a nice youtube as well. Actually this guys adds some additional details, but the principle remains the same. You'll notice that he at one points says" the (atmospheric) air rushes in.



To birng it back to topic on where sounds might come from; obviously not from the vacuum. It's not a very high vacuum, but still it has fewer air molecule than the other side that is open and vents to the air. So, if you hear noises, my experience is usually more along the more mechanical sounds as origin that air, but still, as you will see/understand by now I hope air does go in and out of the booster.

Let me know if this helps you in your understanding of how the booster works.

Jeroen

Last edited by Jeroen : 19th September 2014 at 14:08.
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Old 19th September 2014, 14:11   #71
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Default Re: Noise from the Brakes

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Originally Posted by Jeroen View Post
So on one side of the membrame a vacuum is created and maintained by either the engine intake vacuum or the vacuum pump. The other side of the membrame is open to the atmosphere.
This quoted text was all I needed to understand.

Thanks for the elaboration. Really appreciate it.

Regards,
Saket
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Old 3rd May 2017, 15:13   #72
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Default Re: Noise from the Brakes

Reopening the thread after a long while. I recently bought a preowned 2009 Honda City ivtech S-AT. It is having a strange noise when slight brake is applied or when it slows down to a halt. I have got the original honda brake pads replaced and also tried replacing the rotor disc but the sound is still there. One strange thing is that if I jack up the tires and try accelerating and apply slight brakes the sound is not there. Tried visiting honda workshop but they were not able to find a solution and are now suggesting replacing the hub

The link below showcases the kind of sound I am talking about although it is not my video


Any help would be appreciated
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