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No power brakes hear a air leak inside the cab when I push on the brake.

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The air you hear is coming from your brake power booster, sit under the hood in back of the master cylinder and hook's to your brake peddle, what happen is the booster blew a seal and won't hold vacuum, with no vacuum you will not have power brake's, sooner or later it will go out completely if it hasen yet and the brake peddle will get very hard when trying to stop.There's no repair for this unit just get's replace.

Posted on Jul 06, 2010


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Posted on Jan 02, 2017


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On a 97 gmc truck when you push the brake you can hear air from the brake booster into the cab of the truck and brake travels freely to the floor

When a vehicle is turned off, the brake pedal should remain firm. However, if the driver pushes the pedal lightly and it sinks to the floor, the master cylinder has an internal leak.

Feb 17, 2017 | GMC Cars & Trucks

1 Answer

Brake booster issue in swift

The first thing you need to confurm is the brake warning light on on the daskboard . If it is then its likely a problem with with a leak in the hydrloic system . If brake fluid can get out then air is getting in the system .So check all of the wheels if you have a leak you will see it on the inside of the tire also check inside the cab at the top of the brake pedel where the rod comes from the back of the master cylinder if you see oil them the master is bad . The booster control unit is an anistest system that is powered by your main engine vacuum witch is the 1/2 inch hose connected to it under the hood . The way the unit works is it has a diafram inside it and when you push on the pedel the pressure on the front side of the diafard becomes lower and the engine vacuum draws it forward to asistist by putting more pressure on the master cylinder . Its hard to test but if you can hear a suction noise when you hit the brake and the pedel goes from hard to soft or any combination like this it could be the problem but the hiss noise is a dead give away it dose draw air in but it should not come out when the brake is applyed . And keep in mind that this problem could also be a bad master cylinder that has blowen internialy and would not set the warning light off because there is no leak or in balance in the hydrolic system . But would realy screw with the brakes so they would work one time and be low or high from lock up to vary little brakes the next and the master is also vary hard to test . But brakes are vary redondent and rarly completely fail Good luck with it John

Jun 29, 2012 | Cars & Trucks

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1999 Suburban Chevy, Every time I press the brake pedel I can hear air comming from the rubber boot inside the cab. Is the brake booster gone/going bad?

Usually, a hissing noise when you press the brake pedal is indicative of a leaking brake booster, yes.

While sitting still, idling, have someone else push the brake and grab a piece of garden hose or something, hold it to your ear, and listen up under the dash to find out if the noise is actually coming from that area, or you could also just pinch the line with a pair of vice grips, and see if you still hear the noise.

Your brakes will not cease to function as a result of a booster leak, but if it fails completely, they will become substantially more difficult to use.

Dec 31, 2009 | 1999 Chevrolet Suburban

3 Answers

My power brakes failed and i can hear an air leak,


Dec 09, 2009 | 1999 Dodge Intrepid

1 Answer

I have a 2002 voyager, when i go and press on the brake it makes a hissing sound, i only hear it the loudest from inside the vechicle. when i left the hood up and listen for the sound can't hear anything.

Hi Stevensdorot.
Your problem is a leaking brake vacuum booster.
The booster operates on engine vacuum by assisting the push when you apply your brake. There is a rupture in the diaphragm allowing the vacuum to leak air in when you apply the brake pedal.
The only solution to this is to replace it.

Nov 20, 2009 | 2002 Chrysler Voyager

2 Answers

My brakes are making a hissing noise when i let off the brake pedal. when i press the pedal the noise goes away.

you mean you hear air in the cab down by the pedal. If thats the case your power steering assist is leaking. Its the big black unit behind the brake master cylinder. It may set a check engine light at times for lean condition.

Nov 19, 2009 | 2005 Ford Expedition

3 Answers

Hard brake pedal hear air leaking when pedal pushed

When you press on the brake? Have your brake vacuum assist checked. It,s that bigspaceship looking thing between the brake master cylinder an firewall. good luck and be safe.

May 25, 2009 | 1999 Chevrolet Tahoe

1 Answer

Our S80 Vovlo, as the vehicle is ruuning, I hear a air leakcoming from the brake patel area, as I touch the patel the noises stop and as I let out the brake patel, the air leake strat again, have any

it sounds like the vacuum pipe to the break servo is leaking or it could be the servo diaphragm broken hence you hear the noise in the car, if the brakes are harder to press its most likely to be the servo unit more than the pipe i would also expect you to having a ideling problem due to the extra air in the intake system. hope this helps regards John

May 15, 2009 | 2001 Volvo S80

1 Answer


Likely your power booster is leaking vacuum. If so it needs to be replaced. Noise is under dash near where the brake pedal rod goes into the firewall?

Apr 02, 2009 | 1999 Jeep Cherokee 4WD

1 Answer

2003 dodge dakota

check 2 things first one is their is a plastic check valve that is inserted into the booster (under your hood) then goes to a vaccum line ,then to the engine, pull it out of the booster and check the valve it should be L - shaped. it might have a hole in it causing a vaccum leak. be carefull pulling it out not to break it just pull straight out. if that is ok put it back in. then your problem is going to be the brake booster the big black round case. sometimes the diaphram inside the booster rips causing a vaccum leak which causes a hard brake pedal and you have to stand on the pedal to stop. then you will have to repace the whole thing but not the master cylnder unbolt master cylder with the brake lines connected, the lines will give then disconnect brake pedal arm under dash inside of trk their should be 2 nuts or 4 buts under dash on inside of firewall near brake pedal then remove booster pulls out from under hood. there is not much to replacing them.

Sep 24, 2008 | 2003 Dodge Dakota Club Cab

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