Q: Brake pedal feels spongy.

The feeling of a spongy pedal indicates old brake fluid and/or air in the brake system of your Navigator. While it was mentioned that the master cylinder was replaced three times, more information is still necessary for a proper diagnosis of this issue. I would want to know why the master cylinder was replaced the first time. It should also be asked if this was due to a similar situation of a spongy pedal, or did this symptom develop after the first initial repair.

It is very possible there are a few things going on here with your vehicle. You may have a collapsed hydraulic brake hose or a stuck piston inside one of the calipers. Another possibility I have encountered is when the master cylinder was replaced and the push rod that applies the force to the master cylinder needs to be adjusted. As you can see, because there are so different possibilities for spongy pedal and because any concerns with the braking system is a major safety issue, I recommend enlisting the help of a certified mechanic as soon as possible for适当的诊断。