I did a search and came up with nothing. Maybe I was searching wrong..Anyway my wifey's 2003 Expedition is giving me problems. I thought I had fixed it before but there is a hissing noise that is coming from the inside of the cabin area down by the brake pedal/booster area. Before I noticed a small rubber boot that looked like it came off the brake pedal rod, so I put it back in place. The hissing sound went away..wife was happy for a few days than she told me it was back....is this boot a common problem? The hissing seems to be a vaccum leak since when you depress the pedal the sound goes away until you release the pedal.

Any thoughts?

 

my sons is doin the same thing and Iv searched the whole thing over and cant find the porblem,,,,if you find out wht it is post it here,,,tks

 

Maybe a seal let go on the power brake booster?

 

I don't know????

Like I said, I fixed the boot, but maybe that was just muffling it? Any other thoughts out there?

 

Your vacuum brake booster has a bad seal and needs to be replaced. They sell remanufactured ones so its not too expensive. To confirm diagnosis, with vehicle running and in Park, open hood and remove vacuum line from the brake booster. If that eliminates the hissing inside the cabin, you need a new brake booster. The seals are not serviceable.

 

man I was hoping that it wasn't that.......I will test tonight....

 

Any update on this as my wifes '03 Expy started doing this a week or so ago as well!!
So from the last couple posts, this sounds like a b!tch to replace. Is that right?
Glad I did a search cuz I was about to start a new thread with the same question!!

 

No, it's really not that hard. You might throw a few four-letter words around when you're under the dash, only because of the limited working space.