Brakes Hiss when depressing the pedal

This morning I got in the car (chrysler concorde) which I had let run for about 20 minutes to warm it up as it is -18 with the wind chill today and I pressed down the brake pedal and it hisses like air coming out from under the pedal. If I press it to the floor, it stops. But if I press it and hold it pressed like 1/2 way, the hissing doesn not stop. I drove anyway and the brakes worked fine - just sound like air coming out every time I touch the brake.

Could it be because it is so cold? It didn't make this noise yesterday but the weather turned extremely cold overnight.........I am just afraid my brakes will go out while I am driving......

hey i have the exact same problem. only during cold weather. the hissing starts when i press the pedal. does not seem to effect brake performance. I am thinking that the problem is in the vacuum booster. and i plan on replacing it. have you found the exact problem? BTW i replaced hte check valve. did not change the problem.

hey i have the exact same problem. only during cold weather. the hissing starts when i press the pedal. does not seem to effect brake performance. I am thinking that the problem is in the vacuum booster. and i plan on replacing it. have you found the exact problem? BTW i replaced hte check valve. did not change the problem.

I found the problem.

there was a leak in the brake booster. i bought one at the junk yard and replaced in about 1/2 a day. it would have gone a lot faster if i would have known what i was doing from the begining.

Note also that my original problem was that the brakes did not work at all when the temperature was freezing. this was caused by water that was in the brake booster. the water came in from the leak when moist air came in a condensed.

wow.