There is always this hissing sound when I depress my break pedals, the break is very sharp indeed and there is no known drop in break fluid level I need experts to enlighten me on what to check.
Car model is a ford mustang Boss 302 sorry I must be dreaming its a 2000 toyota sienna.

nurey:
There is always this hissing sound when I depress my break pedals, the break is very sharp indeed and there is no known drop in break fluid level I need experts to enlighten me on what to check.
Car model is a ford mustang Boss 302 sorry I must be dreaming its a 2000 toyota sienna.

Hissing from engine bay or wheels?

Replace your Brake Booster, it's faulty.

X2 on that my jeep has been doing the same thing for almost 2 years buy since I rarely drive it I'll rather fix the steering vibrations first waiting for my Moog steering stabilizer to come in tomorrow ant the replace the TRE at pitman arm

Did you change your brake pads recently

Siena:
Your brake vacuum servo has a leaking diaphragm. Replace the brake servo. And I mean replace, not attempt a repair.

Brakes are safety-related, and the precautions that need to be taken in overhauling can NOT be overstressed.

I guessed there could be air trapped in the brake system cause sometimes I feel something is been poured in the brake after depressing and releasing it, though no known shortage in brake fluid and the break is really sharp.

Inspect your brake pads and change them if neccessary.

Hissing while braking is a sign that your brake pads are finished and need replacement. I learnt that from the owner's manual of my 2004 Honda Accord EX. This is a deliberate mechanism developed by manufacturers to alert you that its time to chnage them pads. If you recently changed your pads, then it is possible that the new pads are not compartible with your car and should be changed.

My kid brother observed same on his Mazda 626 when he changed the brake pads to a more expensive one. After using it for a couple of days, he became uncomfortable with the hissing sound and then changed them pads back to the cheap ones he was using before and the hissing stopped. It could just be the same with your case, you know.