This question refers to my mothers Camry, but I believe its a universal break question. Here is what I know...

She told me her break light came on, and she started hearing a "swooshing" sound when she pressed the breaks. She said it was low on break fluid and when she added fluid the light went off but she still heard the "swooshing" sound. The first thing that came to my mind was that her break pads were shot which would explain the low fluid and the sound. So last night she brought the car by my house and I looked at it and its not what I thought. The pads are in great shape, so I started looking for leaks and could not find any at all. I figured maybe a seal on the mastercylender/break booster was gone, so I checked the booster for fluid and it was dry. Also the pedal is solid and does not creep down as if there was air in the line.

Turns out the fluid was just below the minuim line when she added more so that may just be from normal wear on the pads, and the car may have registered the brake light due to low fluid, so I think that part is explained.

However the "swooshing" sound is still there, (sounds like a tire loosing air). The car does NOT have to be moving to hear it, but it does have to be running. You can not hear it under the hood, but from only inside the cab. If you hold the pedal down its a constant sound, if you pump the breaks it happens each time as well.
I am curious if it is a vacuum leak perhaps, does anyone know what ties the break pedal into the break system that may produce that sound. Or anything else in the break system that may produce that sound?? If anyone needs more info please let me know.

 

The "swoosh" sound (did Nike make the booster?) is normal. The vacuum booster works by opening up a valve when you hit the brake pedal that lets atmospheric air in from around the input rod. This air works with the vacuum on the other side of the diaphragm to create the boost that amplifies your brake pedal force.

So the noise is normal when you push on the brake pedal. (Turn off your radio and pump your truck pedal... you'll hear the same noise)

As for the fluid level... she might have a small leak somewhere. Have her keep an eye on the levels and if they keep going down then you'll have to look for a leak.

 

Thank you sir, I will pass on the news! Have a good one.

 

Well if the pads are low, the fluid is going to appear low. Just plain adding fluid is a bad idea because the break system is closed... so low fluid means low pads or a leak.

Like you said though, the pads looked good... so I really have no idea what problem your dealing with. There has got to be a leak somewhere if its low for no reason.

 

I have not checked her rear breaks (drums) they may be worn a lot more, front pads are better than half so I decided not to replace them yet. I would not be surprised if there was a small leak somewhere but I have not found it yet. I am thinking maybe the rear breaks being old along with the little wear on the front may have accounted for the fluid being low. It was not very low, just below the add line. Will make sure to keep an eye on it though. Thanks.