5-90

You're losing the diphragm in your power brake booster - replace the unit.

You can get them "loaded" (with master cylinder) or "bare" (without) - which you get is up to you. However, considering both it and your master cylinder are probably original, you may want to go ahead and get a "loaded" unit.

CheapCherokee

i had this same problem for a while. The first booster died, making the whooosh sound and affecting the brake pedal. 3 brake boosters and 1 master cylinder later, finally got a good pair.

93XJLI

yea my WJ does this... but its so powerful even with the leak it stops fine.

gotta change it once it gets warm bc its a ***** to take out.

Useless31

If it sounds like it's coming from from your dash and you are loosing pwr assist it's most likely your booster. It's a very simple fix and a new one w LIFETIME warranty is only $80 if you don't have abs you don't even need to bleed your brakes. It's 4 5/8" bolts under the dash, a retaining clip and 4 13mm bolts at the master cylinder. Took a hour to do in the autozone parking lot along with some bloody knuckles.. Ya know the usual. Anyways it's worth it and a very easy fix if you have the 80 to spend, not worth slamming into Simone who stops short on the highway or at a light.. Just my $.02

schmidt46

I have the opposite problem. Mine makes the blowing noise all the time EXCEPT for when I'm pushing the pedal. I also noticed that a few days before this blowing noise began, I started to hear a grinding noise from one of my front brakes. Since it has been cold out I haven't taken a look at my brakes recently, but about 9 months ago may pads were basically brand new.