So I recently bought a 2001 Volvo S80 and I love it, the only issue is a "loose gasket" according to the dealer/mechanic. So there's a hissing noise from the breaks, sounds like air leaking, slows down or stops when accelerating and changes sound when breaking/releasing the break. I was a little concerned at first when I test drove it but then the dealer showed me personally.

The rubber sleeve from the break attached to the firewall is what's causing it, I can make it stop by adjusting the sleeve and pushing it towards the firewall, it usually starts back up again though after driving for a little.

What can I do to stop it? Has anyone else had this issue?

 

I am pretty sure you need a booster.

 

i agree, you gotta replace the brake booster.

 

same.. check the sticky