vacuum leak

[rellik god]

when i step on the brake pedal theres this hissing noise and its not the half moon shaped brake release its up higher on the steering colum theres a release button or something which a vacuum hose is attached to coming from the engine
it also raises the idle when i step on the brakes. what is this switch and how do i fix it. i have a 87 cv wagon lx

[gadget73]

Nothing farther up on the steering column. Sounds like the brake booster is leaking. The only other part up there is the vacuum dump valve attatched to the brake pedal bracket, but it doesn't have vacuum unless the cruise is engaged.

[91waggin]

Just because I've been wondering this for awhile and it's come up, what's the best way to check for vacuum leaks? I seem to recall hearing something about a blowtorch awhile back, but I don't remember exactly what it was.

[Brown_Muscle]

you use a propane torch and put it around the area you believe there is a vacuum leak, if there is a change in idle then there is a leak, however you may need a tachometer to see if there is a very slight change, the idle will go higher if there is a leak. For in engine work you may have to connect a tube to it to reach certain areas

[91waggin]

So if there's a leak it will suck up the propane (I take it you don't light the torch), which will enter the a/f mixture and raise the idle slightly?

[Brown_Muscle]

yup thats the theory haha, Ive never done it but there are plenty of threads on the site with more details, ive read them before, they work on vacum leaks, and gasket leaks, like if you have any leaks in the intake gaskets or what not, I did read that some changes in RPM will be so slight that you need a very precise tachometer to see them, but I wouldn't worry about that, especially if its a leak you can hear, haha


Oh and my brake pedal has always made a hissing noise when you step on it, and when I put it in gear with the shifter as well. Did it just start making this noise or has it always been there? I figured it was normal, but if its not then I'll go take a look at my car as well haha, ive had absolutly no problems braking, and any of the other cars changes RPM slightly when I step on the brakes when its in park. So that should be normal.

its not the half moon shaped brake release its up higher on the steering colum theres a release button or something which a vacuum hose is attached to coming from the engine

Is that switch your talking about to release the parking brake? Mine has an auto release when you put it in drive, works on vacuum.

[rellik god]

thats the part vacuum dump valve attatched to the brake pedal bracket thanks i took out my cruise control. is there any harm to blocking that off

[Brown_Muscle]

no, you actually shud block it off, otherwise youll have a vacuum leak, haha, not to mention who knows what could get sucked into there

[gadget73]

well if you removed the cruise, it shouldn't even be hooked up. Its got 1 hose that connects to a T in a line between two halves of the cruise servo. If there is no cruise servo, there's nothing for it to hook to. That line only ever has vacuum when the cruise is on anyway. If it was leaking, the cruise wouldn't work properly. Thats all.


As far as checking for leaks, I use a vacuum pump and a pair of pliers. Pinch off lines one at a time till it stops leaking, and chase the circuit from there.