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View Full Version : is it normal for brake booster line to hiss when moved a bit?



dbarbau89
10-10-2011, 12:21 PM
A few weeks back i replaced my suction jet pump and while i was doing so i would occasionally brush up against the brake booster line that runs through the firewall. When I applied some pressure to the line to move it out of the way, it hissed. Is this normal or is it indicative of a loose connection or leak? Braking is normal.

Also for my own information, when the motor is shut off and the car is parked, if I press the brake pedal a few times it stiffens up significantly. Is this normal. I have just assumed that it is the left over vacuum that is being exhausted by the brake booster, and that once it is used up, the braking stiffens. That's just a guess on my part though. I don't even know if the booster functions normally while the motor is off.

Thanks for any feedback

Crispy222
10-10-2011, 12:34 PM
Sounds correct. Maybe want to check or just replace the check valve in the brake booster line that runs to the intake manifold. I would assume that after a short time period after shutting the engine off, the brake booster would bleed back any vacuum pressure into the IM.

CamrideA4
10-10-2011, 12:49 PM
A few weeks back i replaced my suction jet pump and while i was doing so i would occasionally brush up against the brake booster line that runs through the firewall. When I applied some pressure to the line to move it out of the way, it hissed. Is this normal or is it indicative of a loose connection or leak? Braking is normal.

Also for my own information, when the motor is shut off and the car is parked, if I press the brake pedal a few times it stiffens up significantly. Is this normal. I have just assumed that it is the left over vacuum that is being exhausted by the brake booster, and that once it is used up, the braking stiffens. That's just a guess on my part though. I don't even know if the booster functions normally while the motor is off.

Thanks for any feedback

From what I've read it's supposed to do that (mine does it as well). I believe it has a small vacuum reservoir and when you move it you're compromising the seal and it's sucking air in. When the car isn't running and you pump the brakes you deplete the small vacuum reservoir and when it's gone that's when the brakes stiffen up.

dbarbau89
10-11-2011, 08:36 PM
thanks guys, that was my assumption as well camride. thanks for the responses.

ballinb5
12-08-2013, 07:53 PM
Hey guys, I have a similar problem. I recently replaced my SJP (suction jet pump), and now I get the hissing noise as well. I can hear it most pronounced when the engine is off and I pull up on the SJP so as to stretch the connections. I feel like it might be the hose line underneath that connects to the diagonal nipple on the SJP, but cant be sure. From reading this, it seems like it could be the SJP itself? Is it possible by moving the lines the SJP releases air...? I think maybe by moving them they stretch and maybe any small fractures get bigger. Thank you for the help!

Do you know where to find a replacement line that connects out of the diagonal SJP nipple? And where does it connect to bc I cant see behind the SJP

ballinb5
12-12-2013, 11:09 AM
bump?

AudiB5owner
12-12-2013, 11:15 AM
Mine hisses as well when I move it around or brush up against it when working on another part. Doesn't hiss otherwise, or when the car is running.

MetalMan
12-12-2013, 11:51 AM
It seems to only do it when you move the check valve enough off its perch that it slightly loses its seal. If you don't touch it, it will be fine. Nothing to worry about, unless it's hissing without being messed with.

ballinb5
12-12-2013, 12:50 PM
Dam that makes me worried, but I'll try to just put it out of mind. I just cant see how moving it an inch loosens the seal, unless its the actual seal inside the valve that loosens.

Anyways, thanks for the help!

Cheers.