hissing sound under the dash, not the brake pads

Below you will find the process form the replacement of this but you will need to bleed the brakes as well. Here is a guide for this as well:

https://www.2carpros.com/articles/how-to-bleed-or-flush-a-car-brake-system

Review this material below and let us know if you have other questions. Thanks

Hi,

replacing the vacuum brake booster isn't too hard. The worst part is unbolting it from under the dash. Also, you will need to remove the brake master cylinder.

If you look through the pics below, they include the directions and pictures which correlate with the directions. These are specific to your vehicle.

I hope this helps. Let me know if you have other questions.

Take care,
Joe