Strange hissing/brakes on my 01

[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?

[Slartibartfast]

Mine clicks when I put my foot on the brake in park too, that's just the shift lock disengaging. It's kind of a safety interlock to keep you from bumping it into gear by accident, or to prevent a kid left in the car from playing with the controls. The hissing sounds like there's a leak in the vacuum pipe between the intake and the brake booster, or a failing booster. If you shut the engine off and step on the brake, does the pedal go hard immediately, or does it take a few pumps?

[PrecisionX]

I messed around with it a little bit when I got home from work. Initially I started cold and heard the hissing, it wasn't loud, more like the sound if you're blowing on hot food. I would drove around the block about 5 times and during that it went away, and then it'd come back temporarily, it gone entirely for about 2 miles of driving. What I DID notice is that after parked I would tap my brake pedal and get nothing, if parked I'd push my pedal in all the way it would come back as the brake pedal was coming back to its original position. It wasn't aggressive like a balloon or tire with a hole in it but I could hear it. If it is the booster or a vac leak how much time do I have before it's a this NEEDS to be taken care of?

 

The clicking in park I may have just never noticed before. This thing is a Texas truck, rust free with 126k on it. It looks like it was just detailed except it never has been detailed

[Slartibartfast]

Hard to know how long it'll hold without seeing it in person. Hard to know if my armchair diagnosis holds water, either. It could even be that the vacuum booster makes that noise normally, though having it come and go does sound suspicious. Depending on how the system failed, you could get weak brakes, a bad vacuum leak, or both. If it still idles fine when your foot's on the brake, and still stops, I wouldn't expect catastrophic failure, but I'd still look into it.

 

From your observation that it comes and goes, I would start with the check valve between the intake and the booster. Easy to get at on a WD21, not sure how easy on an R50, probably not too bad though. IIRC it's just a one way valve, so it should let air through if blown from one side but not the other. If it lets a air through the wrong way, or it's gotten gummed up somehow, clean or replace and see if that makes a difference. Also inspect the hoses it hooks to for cracks, loose fittings, etc. Maybe have someone push the brakes and see if you can hear the hiss from the engine bay.

 

Anyone with an R50 got a better idea what's going on here?