Brake Booster or Master Cylinder?

jpdeuce

Veteran Member
Joined
Apr 8, 2005
Location
Houston
TDI
'05 Jetta Wagon
What's the problem? Have you bled all the fluid out first and turned it all over with good/new fluid?
 

ymz

Top Post Dawg
Joined
May 12, 2003
Location
Between Toronto & Montreal
TDI
2003 Jetta TDI Wagon, 2003 Jetta TDI Wagon
I'm a couple of hours away from the car... only 2nd hand report that pushing down hard on the brake pedal isn't stopping the car... the fluid has NOT run low... (car has over 530,000 miles on it...)

Yuri
 

jpdeuce

Veteran Member
Joined
Apr 8, 2005
Location
Houston
TDI
'05 Jetta Wagon
Moisture or bubbles in the fluid would likely give the same result, so it's hard to tell. At that mileage, who knows though if the MC/booster is original.

Has the fluid been flushed in the last 100k or so? That's the easiest and quickest to do, so I would start there. Don't use the pump method for bleeding though, so you don't introduce stuff into the lines that doesn't ned to be there. Maybe use a different color fluid so you can tell it's all the way flushed.
 

ymz

Top Post Dawg
Joined
May 12, 2003
Location
Between Toronto & Montreal
TDI
2003 Jetta TDI Wagon, 2003 Jetta TDI Wagon
Yes, fluid has been changed often enough... original MC and booster... I was just wondering if there's an easy way to tell other than having a local shop throw parts at the problem hoping that one of them would fix it... (If I'm able to go there, I'd check the vacuum hose going to the booster first, but, as there are no turbo issues, I suspect that the vacuum system's at least functioning...)
 

VE1.9

Veteran Member
Joined
Dec 29, 2012
Location
Chicago
TDI
2002 Jetta GLX 5spd
Pull the vacuum line off from the booster and hook up a mity vac. It will take a while to build vacuum since the brake booster is so large, but it should be holding vacuum and not leaking out air. You would likely also be getting a hissing noise near the brake pedal if it were leaking vacuum.
 

Hyde7278

Veteran Member
Joined
Nov 11, 2012
Location
Central Mich
TDI
2001 Golf GL
Is the pedal hard to press if so It could be the booster or it could be a vacuum leak between the vacuum pump and the booster. Check the plastic hose there known to split. Plenty of posts on it with pictures.
 
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ymz

Top Post Dawg
Joined
May 12, 2003
Location
Between Toronto & Montreal
TDI
2003 Jetta TDI Wagon, 2003 Jetta TDI Wagon
Just spoke to my better half... it appears that once in a (rare) while, the pedal goes to the floor with no braking action... following which, everything's normal... until just last Friday... when things went South in a hurry...

Yuri
 

Chappy99

Member
Joined
Aug 11, 2010
Location
Table Grove, IL
TDI
2002 Jetta GLS TDI MK IV (Manual)
Is the pedal hard to press if so It could be the booster or it could be a vacuum leak between the vacuum pump and the booster. Check the plastic hose there known to split. Plenty of posts on it with pictures.
+1
Just had this issue with those same symptoms.
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
I had that issue right after new years. Just remember that if the master cyl is leaking into the booster it will eat the booster up. Replace them both while its apart.
 

VRTn

Member
Joined
Jan 6, 2015
Location
NB canada
TDI
00 Jetta TDI, 2x 01 jetta TDI, 91 jetta AAZ, 95 GTI VRT - sold
Anyone ever figure out what their problem was? Having the exact same issues with my wife's 2001. I've ruled out the vacuum pump itself, also the hose to the booster. Next step is trying to find a mityvac and test the booster itself. The brakes work like S***. But once you hold the pedal down for a few seconds they lock right on. Also on very rare occasion the pedal will go right to the floor with no brakes at all, as described above
 

indysoto

Veteran Member
Joined
Mar 14, 2004
Location
Eugene, OR
Anyone ever figure out what their problem was? Having the exact same issues with my wife's 2001. I've ruled out the vacuum pump itself, also the hose to the booster. Next step is trying to find a mityvac and test the booster itself. The brakes work like S***. But once you hold the pedal down for a few seconds they lock right on. Also on very rare occasion the pedal will go right to the floor with no brakes at all, as described above
Any work done recently?
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
If the pedal goes "to the floor" it isn't the booster. Either the seals in the master are bypassing or there's a leak in the system.

A leak will cause loss of fluid, bad seals on the master probably won't but might if the secondary seal that contains the fluid is bad too. If it is the fluid will go into the booster.

So...

Pedal to the floor, no loss of fluid indicates a bad master.

Pedal to the floor with fluid loss, look for a leak. If you find one fix it. If you don't the master is bad and the booster has fluid in it.

The delay then sudden lock up seems to implicate the booster but the pedal dropping is another thing. Seems like both the booster and master are bad.
 
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joep1234

Veteran Member
Joined
Jan 2, 2014
Location
NC
TDI
former '04 Beetle TDI, now 2x '15 Audi Q5 TDI's, 2007 Dodge Ram 4x4 6.7
Hold off on throwing money at it. My daily driver was doing the same thing. It would scare the crap out of you and then it work again. There is a fitting on the back of the vacuum pump that gets loose and causes a vacuum leak if the hose is moved. The nipple actually had come loose on mine and all it took was a little RTV once we got it cleaned up so it would stick. The fix has worked for over 9 months now. I almost pulled the trigger on a master cylinder and booster. Basically .50 cents worth of glue fixed it.
 

VRTn

Member
Joined
Jan 6, 2015
Location
NB canada
TDI
00 Jetta TDI, 2x 01 jetta TDI, 91 jetta AAZ, 95 GTI VRT - sold
No major work done recently, I put new brakes on it all around about 3 months ago and bled the whole system but it was doing it even before that. The pedal is nice and high and firm but just feels like the brakes are manual for the first 3 or 4 seconds of pushing the pedal then all of a sudden WHAM full braking power (which I've read several different cases of this happening but it usually always turns out to be the hard plastic vacuum line is cracked). I've replaced my hard line with rubber fuel injection line and clamped it with FI clamps. Checked the one way valve as well it is functioning properly, tapped the vacuum pump tight with a hammer and sealed it, replaced the rubber on the booster/main vacuum line and also replaced the vac storage bottle or whatever it's called, with the one from my parts car. But the odd time here and there (not very often, like once every few weeks) you push the pedal and it sinks down a ways, then you let it go and push it again and it's nice and high. I'm borrowing a hand vacuum pump from a friend and I'm going to test it and see if the booster leaks off. I've also heard you can do a smoke test on them as well. I don't think it has anything to do with the master because the fluid level hasn't went down and I don't have any leaks.... Very strange
 

VRTn

Member
Joined
Jan 6, 2015
Location
NB canada
TDI
00 Jetta TDI, 2x 01 jetta TDI, 91 jetta AAZ, 95 GTI VRT - sold
Hold off on throwing money at it. My daily driver was doing the same thing. It would scare the crap out of you and then it work again. There is a fitting on the back of the vacuum pump that gets loose and causes a vacuum leak if the hose is moved. The nipple actually had come loose on mine and all it took was a little RTV once we got it cleaned up so it would stick. The fix has worked for over 9 months now. I almost pulled the trigger on a master cylinder and booster. Basically .50 cents worth of glue fixed it.
Unfortunately I've already done that, and with two different vacuum pumps and no change
 

joep1234

Veteran Member
Joined
Jan 2, 2014
Location
NC
TDI
former '04 Beetle TDI, now 2x '15 Audi Q5 TDI's, 2007 Dodge Ram 4x4 6.7
I just wanted to share what happened to me. Hate it didn't work for you.
 

VRTn

Member
Joined
Jan 6, 2015
Location
NB canada
TDI
00 Jetta TDI, 2x 01 jetta TDI, 91 jetta AAZ, 95 GTI VRT - sold
Well looks like I will be needing a new brake booster.... I put a vacuum tester to the main vac port on it tonight and couldn't even get the needle to move off of 0. Also tested the one on my parts car out of curiosity ( and thinking maybe I could salvage it) but it went to 15" and then started leaking off after that....
 

jimbote

Certified Volkswagen Nut
Joined
Jul 10, 2006
Location
spiral arm, milky way (aka central NC)
TDI
Tacoma 4x4 converted to TDI
So what about it going to the floor as you described?
replacing the booster in my golf solved the sinking pedal issue, this was after running many quarts of brake fluid through the system with a pressure bleeder and replacing the master... booster was applying more vacuum per pedal input than needed, hence the sinking pedal... i confirmed this by watching brake pressure in vcds ... as the pedal sank to the floor the pressure INCREASED instead of remaining steady or decreasing....this indicated the hydraulics were fine and the booster was at fault.... keep in mind not all abs modules give you the option of monitoring brake pressure, mine has ESP so i could ... sinking pedal due to a bad booster is not just a vw problem but other manufactures have the same issue
 

Patrick shannon

New member
Joined
Nov 10, 2017
Location
Mpls mn
TDI
2006 beetle
My brake pads have been replaced 2006 beetle. but when stopping at slow speeds like coming to a stop sign the brakes are very hard and don't stop like they should. they sink to the floor almost and are very hard feeling..what do you think is happening..? then they are fine at higher speeds..
 

AnotherPerson

Veteran Member
Joined
Oct 24, 2015
Location
New Orleans
TDI
1999 Beetle
Just want to mention this one. Vw has a new set (booster and master) that has replaced all previous revisions. The bolt pattern between master and booster has changed which is why it comes as a full set with the tank. I paid $260 for everything. This isn’t much more than autoparts store remans. And sadly I had a year of problems related to a defective out the box “new” auto parts booster. All has been great since I went to the oem vw one.


Sent from my iPhone using Tapatalk
 

jimbote

Certified Volkswagen Nut
Joined
Jul 10, 2006
Location
spiral arm, milky way (aka central NC)
TDI
Tacoma 4x4 converted to TDI
Just want to mention this one. Vw has a new set (booster and master) that has replaced all previous revisions. The bolt pattern between master and booster has changed which is why it comes as a full set with the tank. I paid $260 for everything. This isn’t much more than autoparts store remans. And sadly I had a year of problems related to a defective out the box “new” auto parts booster. All has been great since I went to the oem vw one.


Sent from my iPhone using Tapatalk
do you happen to have the assembly part number ?
 

ymz

Top Post Dawg
Joined
May 12, 2003
Location
Between Toronto & Montreal
TDI
2003 Jetta TDI Wagon, 2003 Jetta TDI Wagon
Are you sure? The non-ESP and ESP models have opposite bolt patterns and must be matched with their respective boosters...

Yuri
 

VRTn

Member
Joined
Jan 6, 2015
Location
NB canada
TDI
00 Jetta TDI, 2x 01 jetta TDI, 91 jetta AAZ, 95 GTI VRT - sold
Just wanted to give a little update on the situation... i vacuum tested the booster and couldn't even get the needle to move off 0. So I Swapped the brake booster yesterday with the one from my neighbors parts car (which tested good). So come to find out when I get mine off there is a hole burnt in the back side of it , looked like someone had aimed a torch the wrong way....
 
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