01 R50 Cabin Hissing and Brakes?

[PrecisionX]

I get in my Pathfinder this morning only to find that when I apply my brakes and its in park I get a very prominent click from the shifter but once it's out of park it goes away and its only when I apply the brakes and its associated with an air hissing sound in the cabin that goes away when I apply the brake. Pulled out of the driveway and the hissing was there even in drive and again it went away once I applied the brake. What's up?

 

[AlanWrench]

The click in the shifter is the shift interlock that prevents you from shifting out of park without applying the foot brake.

The hissing noise associated with the brakes is likely a bad power booster. It uses engine vacuum to provide braking assist. If the diaphragm is damaged or perhaps something else internally, air can be drawn through the booster into the engine and make a hissing noise.

You can try to verify the booster is the source of the noise by removing the vacuum line from the booster (engine off) and plug it. It's a medium sized black hose, internal diameter is 11/32 of an inch. It runs from the intake manifold, through a check valve and to the booster. Then crank the engine and see if it's making the noise in the cabin still. If not, booster.

-Alan