Brake is soft. It works but quite low. Vacuum booster is giving some hissing noise. Will changing booster fix soft brake problem or do I need to change brake oil or both master cylinder and brake oil.

Thanks
John

 

A leaking vacuum booster can led to a brake pedal being harder to press, not a softer feel. So although your boost is leaking, it is not the source of the soft pedal. Being there is a vacuum leak...it can be the source of your engine running lean or otherwise not smooth.

A soft brake pedal 99% of the time is the result of a bad master cylinder, a leak, or air in the brake line. Air in the brake line only happens if the system has been opened up. So if that hasn't happened then you can rule out air in the system.

Have you lost any brake fluid that you can tell?

 

I am not losing brake oil. The navigaor had both front and rear pads replaced for the last 10 years multiple times. Never had any bleeding. I want to bleed fluid and replace all the fluid. Can I use a vacuum bleeding kit at the caliper fluid outlet. Will it create any problem since the navigator has ABS. What is the best way of bleeding and changing oil. I will appreicate any idea.

Thanks
John