Guys
Ford Ranger 2001
6 V
4x4
122 k miles
Air escaping from the brake pedal when pressed.
Rubber from brake booster is ripped off so I can even feel air coming when pressing brake.
Brakes work fine pedal is firm and does not seem soft and with problem.
what could be a problem ? or if this is a problem ?
Thanks

 

Power assist on brakes works like this:
Engine provides 18-28" of vacuum to the booster which has a check valve to hold highest vacuum inside the booster

Inside the booster are TWO chambers separated by a "rubber" diaphragm
Vacuum in the front side and no vacuum in the rear of diaphragm
The springs in the Master Cylinder and Booster are enough to prevent the vacuum from putting pressure on the Masters pushrod

Inside the cab on the booster is the Atmospheric Valve its a two way valve operated by the brake pedal's pushrod
(there may also be a Cruise Control Vacuum release valve here as well, it is a fail safe for cruise control, it will release vacuum at cruise's throttle cable if brakes are applied)

When you press down on the brake pedal the push rod opens the Atmospheric Valve letting it the 15psi air pressure(sea level), that pressure along with the 20" of vacuum assists the driver in pushing down on the pedal against the spring pressure
When you release the pedal the Atmospheric Valve allows air inside the rear chamber to come out as springs push booster(and brake pedal) back into normal position, this is when you might feel air coming out<<<<

There should be filters on the Atmospheric Valve to filter the air going in but also to quiet the air flow in both directions


To test booster
Start engine
Take foot of the brake pedal and shut engine off
With engine off push down and then release brake pedal
You should get 2 or 3 "power assists" on brake pedal pushes before vacuum is gone and pedal gets hard to press
If not then Check valve on the vacuum hose at the booster is bad or booster diaphragm is leaking internally

If you hear a constant hiss, air being sucked IN at Atmospheric Valve, while engine is running, then internal diaphragm does have a leak

 

Thanks Ron
The only time I hear hiss is when I push or release pedal.
when brake pedal not pressed all is fine and quiet.
and I did test already
and pedal stays hard after 2-3 times presses.
so do You think because rubber on brake pedal's pushrod is ripped off I hear all air noise sucked in at atmospheric valve ?
is it anyway I can only fix this rubber ?
Thanks

 

I don't think the boot can be replaced on its own, it comes with new booster and is already attached

 

is it something to be concerned as a danger while driving ? or is just annoying to hear this hiss ?

 

Just annoying not a safety concern