Frederic Nuyttens

Hissing sound from brake pedal

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When starting the '99 Pajero in the mornings, i sometimes hear a slight hissing noise coming from behind the brake pedal. As soon as i touch the brake pedal slightly (barely a millimeter) the noise stops, and sometimes comes back after a minute. Eventually it disappears. Car brakes fine and pedal does not feel spongy or too hard.

Could this be the brake booster diaphragm or leaky vacuum line ? Is it something that needs urgent attention or could i schedule an inspection with my next PM (in 3000kms) ?

Thanks !

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As discussed on the drive, it sounds like a vacuum leak from somewhere. New point added now that it stops when you touch the brake points it could be booster dying.

I replaced my booster 20-30k kms back and once its dead brake will be very very hard, and you have to literally stamp on the brake pedal with full power to stop the car. The car will stop fine but braking distance increases by 20-30% due to a late reaction.

If your brakes are fine yet, you can drive 3K (hopefully) or let some good mechanic test the leak and advice accordingly.

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I had a similar issue and Gaurav bhai helped me by putting some tape on the hose. It started with the hissing sound and within a week I had to literally stand on the brakes to come to a stop. Replaced the hose and was all OK. Recommend to get it checked at the earliest if it's your daily driver too.

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Sounds like your brake servo is on the way out. It’s totally fine to drive as long as you’re aware. Your brake pedal will get harder over time and you’ll have to stand on the pedal harder to exert the same braking force. You can either change it out now or wait until it gets worse then you really have to change it. An hours work. A second hand unit will suffice. To test a second hand one before you buy, push the rod in and cover the hole where the hose goes in with your finger. The rod should remain in position. If it comes out again, the servo is scrap. 

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