When I press on my brakes I hear a hissing noise and and car barely stops
My car has 134000 miles.
My car has an automatic transmission.
This may be related to your brake booster which is mounted on the firewall, and has what is called a master cylinder attached to it. The purpose of the brake booster is to assist in the stopping power of your car when you press the brake pedal. This is done with vacuum pressure, created by using a small diaphragm inside of it that maintains pressure when you are not pressing the pedal. When this diaphragm leaks and vacuum pressure drops, when you press the brake pedal, this can cause the hissing sound you describe. This hissing sound may also be produced when the master cylinder is failing. I would recommend having an expert from Your Mechanic come to your home to diagnose and repair your braking system. If you need assistance, a certified YourMechanic technician can come to your location to perform an inspection of your hissing brakes or replace your brake master cylinder.