Simple Brake Booster Problem? *Help!*

**00SantorinS4** · 03-23-2012 07:46 PM

Hey guys, I got in my girls car earlier and noticed how stiff the pedal was before I started the car. I didn't think anything of it until after I shut off the car and the pedal was instantly stiff again (couldn't press it down at all) now I know this is NOT normal for these cars as my B5 S4 has a few full pumps after the car is shutoff before it gets rock hard. I was told that the brake booster may be the culprit or possibly a brake Vac line? I know that the pedal shouldn't get instantly hard after the car is shut off in case the car stalls it should still have a vac reserve so you can brake before stopping. I honestly don't know where to start? Has anyone had experience with this problem or can point me in the right direction of where and what to look at in the engine bay? Pics help a ton! Car is a 99.5 A4 2.8 5spd.

EDIT*** Video of issue added. 3/29/12

So I replaced the green check valve with a new one and still no dice with the problem I'm having. The video explains it all. The new valve I have lets me blow air through the arrow side and no air through the other side. The arrow side of the check valve is pointing towards the car and feeds into a small line which looks like it goes into the throttle body. I replaced the Suction Pump/Braided Lines/PCV system/Check Valve/ a couple months ago along with the VC Gaskets/Chain seals/Cam Caps etc.. I even removed the throttle body plastics and completely cleaned the throttle body and the plastic tube that leads to it (Can't believe it's held on my 1 allen screw and the boot was completely letting air out before I cleaned and readjusted it.. I have more power now..) Do you guys know ANY suggestions for me to try and report back? I see 0 leaks in any of the lines and don't feel air coming out of any of the lines. I put soapy water of all of them and saw nothing. Can the suction pump already be bad? It seems to me like it's the check valve or suction pump because when I move the pump/valve in the vid you can hear the air moving a bit with it.
Ignore the bad cat converter/voices in the background. The Cat is next weekends project..

**offroader1006** · 03-23-2012 08:13 PM

check the condition of the check valve on the booster hose. usually the culprit.

**00SantorinS4** · 03-24-2012 03:39 AM

Ok, I'm assuming you're talking about the check valve highlighted in green in the photo below? I just replaced the whole PCV system and suction pump. I totally forgot about the check valve that sits there.
If it is bad, I should be able to blow through both sides?

**00SantorinS4** · 03-24-2012 10:12 AM

I went outside and turned the car on, I'm guessing that check valve must be bad because it's hissing as if air is completely passing through it.
Does the hissing sound like a bad check valve to you guys? All the lines are fine and when I shut the car off it hisses for about 5 seconds until the air is all gone.

**Crispy222** · 03-25-2012 09:34 AM

Yup, its a crack in the check valve. Replace it and it should help your problem.

**00SantorinS4** · 03-25-2012 01:05 PM

Excellent I have one ordered up, hopefully that solves the issue.
Thanks guys

**00SantorinS4** · 03-29-2012 05:29 AM

bump! Video and more detail added to OP. Please help!

**00SantorinS4** · 03-29-2012 11:10 AM

Any Gurus that can chime in on this vac issue?? Certainly someone must be able to make a diagnosis from the video.

**00SantorinS4** · 03-30-2012 05:36 AM

Last bump before I go nuts.

**Crispy222** · 03-31-2012 01:13 PM

you have a leak

**00SantorinS4** · 04-10-2012 01:35 PM

Turns out I had a faulty suction pump.. I JUST replaced the pump when I replaced the PCV system about 6 months ago and it was an OEM Audi/VW Pump!! WTH!
I replaced it today with another OEM one and everything is back to normal, idles much better and holds air now!

**Crispy222** · 04-10-2012 05:13 PM

persistence FTW

**00SantorinS4** · 05-11-2012 09:23 AM

UPDATE: Ok so after examining things further (car still has a rock hard pedal right after car is shut off) I pullled of the brake booster hose and there's 0 suction coming from it.
I suppose this is a symptom of a failed brake booster, correct? The car brakes fine when it is on, so should I make this a priority to replace or can it wait?
Thanks guys

**Crispy222** · 05-11-2012 10:48 AM

yeah, from those sypmtoms and observations, I would lean towards a bad booster. Pretty sure it is just a big diaphram in there. There is a drain hole at the bottom. I've seen a car that was parked for an extended period outside over the winter that had water build up in the rain tray/battery area from clogged drains (under the battery). The water froze in the booster and destroyed it.

**034Motorsport** · 05-11-2012 01:06 PM

Originally Posted by 00SantorinS4

UPDATE: Ok so after examining things further (car still has a rock hard pedal right after car is shut off) I pullled of the brake booster hose and there's 0 suction coming from it.
I suppose this is a symptom of a failed brake booster, correct? The car brakes fine when it is on, so should I make this a priority to replace or can it wait?
Thanks guys

What do you mean there's no vacuum? The brake booster won't create vacuum on its own, but uses vacuum from the motor (crazy machined steel nipple piece in the back of the intake manifold I think on the 2.8). When the motor goes into vacuum, the check valve opens and the brake booster uses the vacuum created by the motor. When you lose vacuum, the check valve closes and maintains the vacuum in the brake booster.

You should only feel vacuum from the brake booster line with the motor on, or when you shut off the car, the check valve should maintain vacuum so when you unplug the brake booster, you should hear a loud whoosh from it escaping.

If you do not, and your check valve and the hose are fully intact, then that definitely would only leave the brake booster as a culprit. With the car running, the booster is probably still maintaining some level of vacuum, but losing it easily, hence the immediately stiff pedal.

As far as whether you should replace it, even though the brakes appear to function normally, you know of an issue with the braking system and its your girlfriend's daily driver; that to me is a damn good reason to fix it. You would never let her drive around with one tire low on air I bet, so don't let her drive around with a brake system that has a fault, even if it "seems" fine.

Junkyard FTW>

**Crispy222** · 05-11-2012 01:25 PM

It stops fine due to the continuous vacuum from the v6 and the leak is probably very small. So there is enough assist when running. If the engine were to die at highway speed, it might be a scary situation for someone un-comfortable with non-powered brake.

**00SantorinS4** · 05-12-2012 04:53 AM

Im almost positive it is the booster and will most definitely get it fixed for her. If I take the brake booster hose and blow into it when the car is off, it doesn't hold air. The air just escapes as I'm blowing into it. I may try to DIY but it looks like a major pain to replace..

**ballinb5** · 12-08-2013 07:51 PM

Hey guys, I have a similar problem. I recently replaced my SJP (suction jet pump), and now I get the hissing noise as well. I can hear it most pronounced when the engine is off and I pull up on the SJP so as to stretch the connections. I feel like it might be the hose line underneath that connects to the diagonal nipple on the SJP, but cant be sure. From reading this, it seems like it could be the SJP itself? Is it possible by moving the lines the SJP releases air...? I think maybe by moving them they stretch and maybe any small fractures get bigger. Thank you for the help!