Hi,
If the brake pedal slowly goes to the floor and there are no obvious leaks, the master cylinder is likely the problem.
I noticed you replaced three brake lines. Therefore, I would imagine when they failed, the brake pedal went to the floor. What happens is this. Inside the master cylinder, there is a specific range the plungers move in. Over time, corrosion builds up in the areas not used.
When the brake pedal goes to the floor, the plungers hit the corrosion and are damaged. This allows brake fluid to bypass them, and the pedal goes to the floor.
What I suggest is this. First, take a look through this link.
https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor
If the link seems to mirror what you experience, there are no leaks, and the pedal slowly goes to the floor, replace the brake master cylinder.
Here is a link explaining how it's done:
https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder
If you look at the attachments below, they are the directions specific to your vehicle.
Hope this helps. Let me know if you have other questions.
Take care,
Joe
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Sunday, October 3rd, 2021 AT 8:12 PM