The brakes are fairly new, but they are going to the floor and sometimes not stopping well. I hear a squeaking noise in the morning when the car hasn't been driven. I called a couple of shops, and they said there was a problem with the master cylinder or booster.
Hi. It sounds like a hydraulic issue. If there are no external leaks in the hydraulic system and it is full of fluid, yes, the master cylinder sounds to be faulty. The pedal goes to the floor because the master cylinder developed and internal leak. The leaking pressure causes the pedal to go to the floor. A booster is ran by a vacuum and the failure feels completely different. Booster failure causes the pedal to get very stiff and often requires you to step on the pedal with both feet to get the car to stop. Replacing the master cylinder will require bleeding the cylinder and the system after replacement. If you need further assistance, I recommend you have a certified technician, like one from YourMechanic, inspect the brake system on your vehicle and suggest an appropriate repair.
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