I am being a rebel and posting this here because I am getting no love in the stock issues forum.

I know there are a few other threads on this, but I want to be very specific, becuase I am trying to decide if I need to drive 2 hours to get this checked.

I am hearing a hissing noise that seems to be coming from the pedal area. I hear this when I let off the brake or the accelator (so basically when I am coasting.) If I depress the brake, it stops, but as I let it off, it starts again. If I depress the gas, it stops... well, you get the picture. The strange part is, if I gently tap the brake the hissing stops, even if when I am coasting (still in drive, my mini's an automatic, but I am not pressing the brake or gas.)

I do not hear this noise when in park or when the engine is off. I don't have the hardness that I have seen mentioned in the other posts on this topic. I pushed my brake 10 times with my car off and it still depressed just fine.

The noise is not excessively loud. It gets louder the faster I am going, and I really only hear it if the ac and radio are off.

I have had a friend who is a mechanic look at it, and he thinks it is a vacuum leak in the booster. I really have no idea.

My MINI has 55k miles on it. I talked to the service center in Indy (2 hours away) and they said if I bring it in, they can see if MINI will still cover it at least partially since the brakes are a vital part of the safety of the car. They told me that they have never had to replace a brake booster on any MINI, though, so I think they are doubting that that is what it is. (I find this doubtful)

So, my first question is, is it possible that this noise is normal? (fingers are crossed)

Second, Is there anything besides a brake booster vacuum leak that would cause this?

If not, should I drive to Indy, have them diagnose it, probably have to drive home then back to drop it off so they can order the part and MINI may cover it partially.. or... should I just purchase the part directly for $350 and have my mechanic replace it?

Also, if it is a vacuum leak, is there any way to fix it without having to replace the whole master cylinder?

One more thing... If it is just a vacuum leak, what harm am I subjecting myself and my car to by just driving it as it is?

Update and more questions... I spoke with the Mini service manager and he said that the brake light should be lit if there is a vacuum leak... I thought about his, and I actually had to get new brake pads right after I got my MINI (3 months.) I kept hearing a hitting noise, and it was actually where the pads were so wore that the edge was hitting or something like that.. My mechanic was shocked that my brake light never came on because they were almost bare. I'm wondering now if my warning light is malfunctioning. My brake light has never came on since I have had the MINI.

Thanks in advance!

 

i am bumping myself in hopes that someone will give some input....

 

This is the symptom of a leaking brake booster. There is a valve inside where the pedal connects which will sometimes go bad, causing a vacuum leak while the engine is running. The reason why the hissing stops when you press on the gas is because the engine no longer develops vacuum at part throttle on up.

The test for a leaking booster is simple. Shut off the engine and wait a few moments. If the pedal is hard to press, the booster has a leak. Also, the hissing sounds is a sign of a bad booster. These have been a minor issue with MINIs. There is no vacuum sensor on the booster which could be used to signal a failing booster, unfortunately.

The only solution is replacement. While there is no immediate harm that can come from operating the car as such, you could run into situations where the brake pedal might require more force to bring the car to a stop. The brakes do not diminish in capacity or fail, just the amount of assist from the booster changes. A heavy vacuum leak can confuse the engine control computer and set a check engine light in rare cases.

 

I had a similar problem a couple of years ago. The hissing was driving me crazy. I finally was able to get the dealer to replace the brake booster under warranty.

If you do a search in the brakes and tires forum, most post describing the problem and solution should come up.

Good luck, Dianne

 

thank you greatbear and blue_rocket2 for all the info.

I did try the test, and my brake pedal is still easy to press after the car is shut off. Does this mean that the brake booster isn't the issue?

 

Did you wait a couple minutes before you tried?

 

Yep.

 

Then i have no idea. This has all the symptoms of a brake booster leak so i dont know what else could be going on.

 

BUMP, good luck