Brakes feel "funny". Brake booster? Master Cylinder? Vacuum pump?

Shenandoah

Veteran Member
Joined
Jan 9, 2008
Location
Shenandoah Valley, VA
TDI
2005 Jetta Wagon; 2005 Beetle; 2004 Jetta; 2002 Golf (three of them); 2002 Jetta Wagon; 2000 Audi TT->TDI; 1999 Beetle
Folks,
This is my 2000 Audi TT > ALH conversion and my daily driver. The other day when I came home from work I noticed my brakes felt "soft". The pedal seemed to travel closer to the floor than previously. I also noticed a "pffffff" sound when I put the brakes on. No noise when the pedal came back up. Braking was ok, it's just the pedal traveled further than I was used to.

I inspected the hard line between the vacuum pump and the brake booster. No cracks or leaks. I know the check valve is bad, but for this test, it's not in use. I put the hard line back on and connected my might vac to the nipple on the check valve. Started the car and have 27" of vacuum at idle. If I step on the brake pedal and hold it, I loose about 3-4" of vacuum and the vacuum holds steady. When I let up on the pedal, vacuum drops down to about 10"-15" and takes 10-12 seconds before it's back up to 27" vacuum.

If I pump the brakes rapidly 4-6 times, vacuum drops down to almost zero. Once I stop pumping the brakes it takes about 10-12 seconds for vacuum to build back up to 27".

I've got several VWs and don't notice the "pffffff' sound on them when I put the brakes on. If I listen closely I can hear a slight "pfffff' sound on the others, but no where near as noticeable on the TT. My guess is the brake booster is going bad?

Does it sound like the booster is failing? If not, what else should I check. Thank you.

Eric
 

Schoust

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Joined
Oct 22, 2013
Location
Litchfield County
TDI
00 Jetta Alh 5spd
Sounds like a vacuum leak. If you can hear a pfff noise coming from under the dash drivers side more than likely you will need a new booster...
I did.
 

joep1234

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Joined
Jan 2, 2014
Location
NC
TDI
former '04 Beetle TDI, now 2x '15 Audi Q5 TDI's, 2007 Dodge Ram 4x4 6.7
Check the hose barb that comes off the vacuum pump. They sometimes come loose in the housing causing the problem you described. I have an '04 that was doing the same thing. Sealed the barb and it stopped. My son had the same problem and was solved the same way.
 

Shenandoah

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Joined
Jan 9, 2008
Location
Shenandoah Valley, VA
TDI
2005 Jetta Wagon; 2005 Beetle; 2004 Jetta; 2002 Golf (three of them); 2002 Jetta Wagon; 2000 Audi TT->TDI; 1999 Beetle
Schoust,

Yes, the sound is coming from in the car under the dash on the drivers side where the brake booster comes through the firewall. When I push the brake pedal with my hand I hear a "pffff" around the booster/master cylinder rod. It's only as I press the pedal down that it makes the noise.

vacuum pump barb is tight. With the car running I get 27" of vacuum off the check valve on hard line between the vacuum pump and brake booster.

Looks like I'm replacing the brake booster and master cylinder. The car is 17 years old, so I wouldn't be surprised if the brake booster is failing.

Eric
 

Shenandoah

Veteran Member
Joined
Jan 9, 2008
Location
Shenandoah Valley, VA
TDI
2005 Jetta Wagon; 2005 Beetle; 2004 Jetta; 2002 Golf (three of them); 2002 Jetta Wagon; 2000 Audi TT->TDI; 1999 Beetle
Folks,

Just to follow up. This morning I pulled the master cylinder off the brake booster (leaving the hydraulic lines connected). The end of the master cylinder that goes in to the brake booster was slightly wet. I took a flashlight and looked in brake booster and could see a pool of brake fluid in there......

I ordered a new brake booster/master cylinder.

Eric
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Folks,

Just to follow up. This morning I pulled the master cylinder off the brake booster (leaving the hydraulic lines connected). The end of the master cylinder that goes in to the brake booster was slightly wet. I took a flashlight and looked in brake booster and could see a pool of brake fluid in there......

I ordered a new brake booster/master cylinder.

Eric


What booster did you get? I had all kinds of issues after changing both and I ended up having to get the new upgraded Vw parts. The new stuff comes as a set because it's not interchangeable with what's already there. And it was only a few dollar less than a cheap auto parts store setup.


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Shenandoah

Veteran Member
Joined
Jan 9, 2008
Location
Shenandoah Valley, VA
TDI
2005 Jetta Wagon; 2005 Beetle; 2004 Jetta; 2002 Golf (three of them); 2002 Jetta Wagon; 2000 Audi TT->TDI; 1999 Beetle
AnotherPerson,

I ordered a Bosch brake booster from one of the vendors here on the forum (not sure if I can mention the name?) along with a new master cylinder.

Eric
 

AnotherPerson

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Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
AnotherPerson,

I ordered a Bosch brake booster from one of the vendors here on the forum (not sure if I can mention the name?) along with a new master cylinder.

Eric


Didn't know Bosch made them for our cars. I would think it to be a quality part though if it really is.


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Shenandoah

Veteran Member
Joined
Jan 9, 2008
Location
Shenandoah Valley, VA
TDI
2005 Jetta Wagon; 2005 Beetle; 2004 Jetta; 2002 Golf (three of them); 2002 Jetta Wagon; 2000 Audi TT->TDI; 1999 Beetle
AnotherPerson,

Yes, the original brake booster were made by Bosch. I'll post on the replacement process later this week.

Eric
 
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