Check around brake pedal for something rubbing. If OK, I'd look into the master cylinder.
If the brakes on a Mazda 6 are squeaking, it could be indicative of a problem. The brake pads could be incorrectly set.
un equal adjustment of brakes will cause one brake to apply earlier and harder than other brake
Could be inferior brake pads or glazed brake rotors. If the new pads were installed without machining or replacing the rotors that could also cause brake squeal.
Only use products designed to clean brakes. Most auto parts stores carry brake cleaner. If you use anything else it could leave a residue that could cause your brakes to fail.
Could be low on brake fluid. If it is low you either needs brakes or you have a leak in the system.
brake caliber
Usually, a loss of pressure in your brake system means that there is a hole somewhere in the system. A leaking brake line or a punctured reservoir could cause a loss of pressure. A bad master cylinder could also cause a loss of pressure in the back brakes.
The cause can be traced to a few things. Number one the master cylinder may have failed. Number two you could be low of brake fluid or have none at all due to a leak or broken brake hose. If the power brake booster fails you may think you do not have brakes because it requires an excessive amount of pressure on the pedal to activate the brakes. Whatever the cause do not drive this car into you have the brakes repaired.
It could be a bad cylinder, bad springs, bad emergency brake, or could need to be adjusted.
There are a lot of different things that could be wrong. But initially what it means is that your brakes are going out or are out You should start by checking your brake fluid if that is low it would cause you to loose pressure. If your brake fluid is low and you fill it things should get better if you don't have a hole in your brake line. If the fluid is full check your brake pads
Probably a rotted out brake line sprung a leak, check the brake fluid reservoir.
worn front end parts (steering or suspension) could cause a car to shake when appling the brakes.