ccutaia1 Report post Posted July 20, 2017 I have a 2007 36' class A Ford chassis motorhome with ABS brakes. I noticed that when I hit the brakes hard I hear a hissing noise. I also hear it if I am standing still and press hard on the brake pedal, is this normal? Share this post Link to post Share on other sites
wildebill308 Report post Posted July 21, 2017 Yes this is normal. Be glad you hear it. You have a hydro boost not a vacuum boost and what you are hearing is probably the fluid in the system. When the engine is running the booster is run off the power steering pump. When the engine is off it is run off a electric motor for the booster. Some units are noisier than others. Bill Share this post Link to post Share on other sites
