Air leak brake pedal

[Vang1]

Hello

I have a 2011 Avensis Diesel Estate
When stopped outside a shop last weekend i heard a Hissing/air leak noise comming from my brake pedal..
When i pumped the brake many times it disspeard every time the pedal was pushed. and came back when the let go of the pedal.

After several more pushes it did go away.. also heard this while driving... it was a loud like "Air leak" sound. the brakes a working.



The airleak comes from this part.. the rubber part there. tha sound dissapeard if i pressed my hand around the rubber part behind my brake pedal..

Is this normal ? or do i have to change the whole brake booster ? and can this be fixed by changeing just some small rubber gasket ?

yesterday i drove for 3 hours without hearing the noise, but the noise was there the day before that. but the sound dissapeard when i pushed the brake pedal rapidly many times.

[Vang1]

Here is a video i found online with the same problem i have. i dont have this problem at the moment, just happends 3 times the last week.
so i guess its a problem that is starting to get worse.
 

[Red_Corolla]

It's air leaking past the pushrod seal and into the servo. This could cause complications on a petrol engined car, but as you have a diesel, the vacuum is supplied by a pump and the leak shouldn't cause any side effects.

I would still attend to it in case the leak gets worse and you start to lose braking performance. I don't know if it's serviceable or not, but I would start by checking if there's a seal kit available for it.

[Konrad C]

On 11/8/2021 at 1:26 PM, Red_Corolla said:

It's air leaking past the pushrod seal and into the servo. This could cause complications on a petrol engined car, but as you have a diesel, the vacuum is supplied by a pump and the leak shouldn't cause any side effects.

I would still attend to it in case the leak gets worse and you start to lose braking performance. I don't know if it's serviceable or not, but I would start by checking if there's a seal kit available for it.

Just to correct and say that the Mk3 T27 Valvematic petrol engines, also use a vacuum pump too! This is due to the way the engine works with throttle mostly open, and the valves control inlet mixture through timing, duration and the amount open. This means there is not enough vacuum to operate the servo brakes. Valvematic engines will not be affected. Yes, the previous generation petrol engines like the ZZ and AZ series are conventional, so could affect the engine running. 

So the question is , how much is effecting braking performance and pedal effort? If a safe liquid is sprayed in the general area of the suspected sound, does the pedal feel and performance change? If testing, make sure it is done in a safe place!