Brakes and sucking sound

[colinnwn]

The Pathfinder is having a tough week, fortunately the problems have been relatively easy fixes, if not exactly cheap.

 

Now when I am in the truck idling with the brake not on, I hear a sucking sound from under the dash. If I press on the brake it goes away immediately. If I start accelerating it goes away slowly.

 

Pretty classic sounding vacuum leak. So far braking is still good and engine isn't running rough. What is strange is outside the truck I can't hear it.

 

I assume it is a bad brake booster. Wondered if anyone else had experienced this to confirm? Or if anyone has replaced the brake booster and has advice?

[01Pathmaker]

Unfortunately, it does sound like your booster is on its way out. I've never done one on an R50 so, sorry can't help with procedures.

[colinnwn]

I read on another forum where replacing the check valve fixed it. It is so cheap and easy to replace that I will try that first. The Nissan one is now $20, and auto part stores only carry a generic for most applications for $5. Haven't decided which to try.

 

The Nissan brake booster is an astronomical $650. I have no idea what justifies that price. If I have to do it, I'll go with an O'Reilly rebuild for $220

[colinnwn]

I checked the check valve which was fine.

 

I read on another forum where the grommet around the brake pedal push rod can come out and cause this. It is so tight for space under the dash I'm not looking forward to this. And so far the Pathy has only done this 2 mornings. But I guess ill have to investigate more.

[fixinto]

i cant remember if there is anything under the dash vacuum actuated.. i dont think there is but i briefly scanned that section when i was looking at in cab air filter location. Does messing with your climate control stuff have any effect on it, or changing which vent you are blowing out of. like the diff in defrost and floor. /shrug. very long shot. hope you get it worked out. but it probably does have something to do with the brake booster. Especially if there isnt anything else vacuum actuated.

 

Pat

[Slartibartfast]

If you can get ahold of a smoke machine, and hook it up to your intake, you might be able to find the leak more easily. The shop I worked at for a while had one that took shop air and baby oil and put out a really dense smoke. It was great for finding bad injector O-rings, vacuum lines, that sort of thing, so I imagine it might help you with the brake booster too.

 

I made myself a ghetto smoke machine the other day out of a 12v tire pump and a Mason jar with a cigarette in it. I haven't tested it on a car yet but it does blow gobs of smoke for a minute or so until it uses up the cigarette. It does smell a lot worse than the shop machine...

[colinnwn]

Funny you mention the HVAC controls. They are all cable activated air doors and an electrically operated recirc door. I just got finished replacing the HVAC control assembly. Going to do a short writeup on that one. I did mess with the cables manually at the same time as the sucking sound, and no change.

 

So far it is too intermittent to be able to test with a smoke machine, unless I want to be late to work and pull over on a cold morning to do it. Hopefully when it gets more consistient, the power brakes continue working well for a while, to give me time to diagnose further. It could end up being a rush job to just replace the booster and hope it fixes the problem, now I'm convinced the most likely cheap solution isn't the issue this time.