Hi everyone. I have a 99 s80. It has 100k on it . Runs good and drives like a race car. The break is doing the vacuum hissing noise. I have been doing some reading on this forum and believe it is the break booster. If anyone can confirm this that would be great. I also need a part name and # and a good place to order the part. I am going to try to do it myself. Any advice or tips would be much appreciated. Thanks Ron

 

Yes sounds like a bad Brake Booster.
But you would have to get the Part # from the Dealer most likely.
They will need to know info about the car to find the right part #