Brake Booster

[QuintenJ]

I have a 1993 Ford Explorer. Just the other day the brakes were working fine. Then seems like overnight the brakes aren't working right. The brake pedal is very very hard to press and doesn't stop the car like it should. If I press on the brake long enough in drive it stalls. I did the test of pressing on brakes couple times with car off then held brakes and turned car on and the pedal didn't move.

Also when pressing the brake there is a hissing sound coming from under the dash?

Any suggestions would be appreciated before I go buy parts.

 

[ExploreHudson]

Sounds like a vacuum leak going to the brake booster. Check the rubber lines, and if squeezing them or adjusting them changes the idle, they need replacement

 

[QuintenJ]

Alright I will check after work. Thanks for the suggestion.

 

[ExploreHudson]

Another way to check for the leak is go under the hood with some incense, or a cigarette if you still actually smoke those, and look to see where it gets pulled into. You can also spray carb cleaner around the hoses and listen for a change in RPM.

Maybe something finicky with the brake pedal itself? I know that there are a few electronic sensors there, perhaps one of them has a vacuum line? I have no idea.

On top of that, it could be that the brake booster diaphragm itself gave out. I've had this happen on other cars with unknown mileage boosters on really hot days..