Brake pedal erratic

Hi and thanks for using 2CarPros.com.

Based on your description, it sounds like the master cylinder is failing. There are plungers which force brake fluid through the system when you apply the brakes. They should not allow fluid to bypass them. However, when they get older, often times that is what happens. If you press the brake and hold pressure on it and it slowly goes to the floor, the master cylinder needs replaced.

Here are a couple links you may find interesting:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

If you determine the master cylinder is bad, here are general directions for replacing one:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Let me know if this helps or if I misinterpreted what you meant. Or if you have any other questions, please feel free the ask.

Take care,
Joe