Question about 2003 Ford Expedition

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There is a hissing sound that is coming from the firewall behind the brake that stops when I apply the brake pedal.

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Your brake booster is leaking internally. this is a one piece, non serviceable component, and the entire assembly must be replaced. good luck!

Posted on Jul 07, 2010

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1996 Buick Park Avenue Ultra making a hissing noise when I press Brake Pedal. Have to Press super hard to stop or slow down.


Sounds like a possible air pocket in the braking system. Do you know how the bleed the brakes? They may need to be bled. Also, if you've added brake fluid recently, and didn't put the cap back on, it could create a suction. Another note is to check the cap to the brake fluid reservoir. It's rare, but, it could be bad.

Jul 10, 2013 | Cars & Trucks

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Brake Problem


yes but up to a point
the brake pedal should move about 1" to take up the pedal free play and then be applied smoothly as you press further
the harder you press the more solid stopping action you will get
that way you can feel the brakes working so that you can adjust the braking action for stopping
there should be no hissing noise that occurs when the brakes are being applied
you say hydro booster which is hydraulic booster but a hissing noise will come from an air leak in a vacuum brake booster which indicates that it needs repalcing

Apr 16, 2017 | 2001 Dodge Durango

2 Answers

My brake pedal hisses when i apply perssure on the pedal


if it is squishy when you press it you may have air in the lines and you need to bleed them out.

Jun 30, 2011 | 1991 Chevrolet S-10 Blazer

1 Answer

When releasing the brake pedal theres a loud hissing sound coming from inside the car down around the brake pedal. it does not seam to affect the braking of the car. the brakes seam to work just fine but...


Sounds like you have a leaking brake booster. The booster is what supplies the power assist to the brake pedal and is located in between the firewall and the brake mater cylinder.

Eventually it will get bad enough to cause either the check engine light to come on for lean codes or cause the engine to start to idle poorly and possibly affect you ability to apply the brakes.

This is a relatively simple repair. You can remove the master cylinder from the booster. Leave the brake lines attached. Most of the time you can gently move the master cylinder out of the way and the lines will bend or flex with the movement. You only need to move the master cylinder just enough to squeeze the booster in and out. Then remove the vacuum line from the booster.

The booster is held to the firewall with four nuts that can be accessed under the drivers side of the dash. First remove the rod that attaches the booster to the brake pedal. Then remove the nuts that hold the booster to the firewall. Remove the old booster and install the new one.

Nov 26, 2010 | 2000 Jeep Grand Cherokee

1 Answer

Replaced rear brake pads, now there is a hissing sound coming from brake pedal when i start it , come to complete stop and after i turn car off .what is the hissing or air pressure release sound coming...


There are 2 things that can use vacuum near the brake pedal. If you have cruise control, there is a safety switch on the pedal to shut off the curise when you apply the brake. This switch may be leaking.
The other part is the brake booster, which is actually in the engine compartment but bolts to the firewall, and your brake pedal mechanism pushes into the booster. You will need to get your head under the dash with the engine running and press on the pedal to locate the leak--on the switch or on the wall.

Sep 07, 2010 | 2004 Ford Expedition

3 Answers

Its a constent hissing from my brakes in my Mazda 2001 tribute. The noise does stop When i press on the brakes but as soon as i let off them the hissing continues. Ive read it could be the brake booster. ...


It is the booster, but it might not be abnormal.

Vacuum from the engine is supplied to the booster, and vented if the brakes are not being applied.

When you step on the pedal, the movement of the pedal blocks the vents, allowing the vacuum to build up. That vacuum then pulls on a diaphragm, assisting you in applying the brakes.

Most people can’t hear that venting, some can.

You should, of course, have it checked out, but it sounds as if this might be normal operation.

The booster is bolted to the firewall, and then the brake master cylinder is bolted to the forward side of the booster.

To replace it you disconnect the brake pedal, remove the master cylinder, take the vacuum line off the booster, unbolt it from the firewall.

Install the new booster by reversing these steps.

But I don't think you need one, from what you say.

Aug 11, 2010 | Mazda Tribute Cars & Trucks

3 Answers

2005 Ford Escape Hissing sound


The power brake booster has a bad valve. I can't suggest where to find a new valve for it, but you can buy a rebuilt replacement. They are usually not hard to put on.

Jul 02, 2009 | 2005 Ford Escape

2 Answers

Air/Hissing Noise from Brake Pedal


this noise is caused by a defective power brake vacuum booster, (big round thing behind the master cylinder) the diaphragm is leaking vacuum.

May 06, 2009 | 1995 GMC Suburban

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