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Earlier this week when i stepped on brake pedal it would hiss. Now it's a constant hiss as long as the engine is running

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It sound like you have a vaccume leak in the hose running from your master cylinder to your engine

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My brake pedal will not budge, and a hissing noise present when running

The stop lights won't go out until the pedal is depressed, as there is a switch which is activated by the pedal.

A hard brake pedal is probably caused by a defective servo. The hissing noise is probably an air leak in the servo.

Switch the engine on, open the bonnet (the hood..) and see if you can locate the hissing - that'll probably be in the brake servo area.

If you don't know what a brake servo looks like here is a generic image:


Jan 27, 2016 | 1989 GMC Sierra

1 Answer

Brake pedal hiss

Brake servo leaking

Aug 30, 2014 | Audi A3 Cars & Trucks

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How do I tell if the power brake booster isn't working on a 1998 Ford explorer?

When you turn off the motor & step on the brake
pedal 3 times, it should get hard

Then start the motor & engine vacuum should allow
the brake pedal to go almost to the floor

If you hear a hiss under the dash it (may) be bad

Aug 13, 2014 | Cars & Trucks

1 Answer

When I hold down my brake pedal on my au xr6 ford I hear a hissing sound and when I pump my pedal up with the ignition off then start the car my pedal doesn't move the pedal is very hard when I do eme

Sounds like you have a defective vacuum assist brake booster... Make sure you have a good vacuum supply with the engine running before condemning booster. If vacuum supply is between 17-20" of vacuum at idle and it is properly concreted to booster then the booster is defective

Jul 15, 2014 | 1999 Ford Falcon

1 Answer

Why when I step on brake an hear hissing noise under dash?

If nobody has helped you yet.....I have 2 things that are possible; 1st is the vacumn assist booster, while it sits in the engine side of the firewall your brake pedal is connected to it, it serves to 'amplify' your pedal pressure. A vacumm leak into the cab compartment may cause the hiss and the inconsistency in the way the brakes grab. The second may be a cruise control switch the earlier ones were controlled by vacumm but I do not know when they switched to electronic controls but this would have nothing to do with the break 'grab'. Best of luck.

May 27, 2014 | 1997 Dodge Caravan

1 Answer

When bleeding brakes have good pedal with engine off. with engine running pedal goes almost to the floor what is wrong

can you here a hissing sound when you push the brake while its running? if so then you have a bad brake booster, need to replace it, the hissing is actually the vacuum that builds within the booster escaping thru the seal in the booster

Sep 09, 2012 | Oldsmobile Intrigue Cars & Trucks

1 Answer

Why would my brakes hiss when I step on them and cause the engine to rev up when I do this? It also makes the vehicle very hard to stop.

It sounds like your brake booster is leaking. The air hissing is the air going into the leak. This extra air goes into the engine and causes the engine to rev up. The booster is what makes it easy to push the brake, (when it is working correctly) which is why the pedal is hard to push.

May 31, 2012 | Chevrolet Blazer Cars & Trucks

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

1 Answer

When u press on the brakes on my expedition, i hear air escaping.

If it is a constant hiss with your foot on the pedal, you have a bad brake booster. If you hear a hiss, and nothing else while holding the pedal, it is the air escaping from the booster boot, and should not pose a problem.

Jun 11, 2009 | 2003 Ford Expedition

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