S4 B6/7 brake hissing sound

[Dondbg]

I hear hissing when I press down the brake pedal, the braking is crap, and my pedal will run to the floor when pressing on it (it won’t do it on its own); I still can stop the car if I pump the brake few times, of course, I'm not driving it.

Inside: https://youtu.be/0eOV9YQiJrM

Outside: https://youtu.be/fpmAS1ejD4I

I Bled the brakes with a power bleeder and the traditional way, with no air or leaks.

Is it the MC, booster or both?

[Atomic Avant]

How is your fluid level?

Sounds like air escaping past a seal in the booster to me.

[Zolli]

I agree with Nips.

Weird, though

[09SCiduA]

You need a new booster...how did the booster lip get marred up; it could be the culprit...? JB Weld that lip or swap it out

[Dondbg]

Fluid level is ok.
I thought fluid escaping to the booster and if so I should see some in the vac hose getting sucked in to the manifold ?
Still if it’s the booster only then why the pedal run to the floor.

It’s like both failed in the same time > weird

[Atomic Avant]

Fluid level is ok.
I thought fluid escaping to the booster and if so I should see some in the vac hose getting sucked in to the manifold ?
Still if it’s the booster only then why the pedal run to the floor.

It’s like both failed in the same time > weird

I mean for the cost and hassle I would just replace both.

[Dondbg]

I mean for the cost and hassle I would just replace both.

Agree. that what I have in mind since I got a used booster and MC.




But want to know which one is faulty.

[Zolli]

Probably the booster - the vacuum diaphragm must have a leak. My two cents anyway

[Dondbg]

Probably the booster - the vacuum diaphragm must have a leak. My two cents anyway

But that will not cause the pedal to run to the floor, that’s a bad MC.
I discounted the booster vac hose, plugged thr intake manifold side and started the car, i lost power braking, this tells me it works.

[Dondbg]

Replaced booster and MC and brakes are back.

By the look of it. I had a faulty MC.

[Atomic Avant]

Replaced booster and MC and brakes are back.

By the look of it. I had a faulty MC.

Glad you got it sorted. Poor braking is nothing to ignore!

Did you figure out what failed with the MC?

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