# MC messed? MK4



## off the grid (Apr 1, 2008)

Hey all,
Car is a '03 Jetta Wagon 1.8T.
Problem:
My pedal is solid at first press and the car stops great, but at a stop the pedal will sink to the floor. Is this my Master Cylinder? last car I had a master fail had to be pumped and pumped and pumped to stop.

The back story...
Through the winter I had total fade out a few times after only a few stops on back roads from 80-90mph. Brand new stock rotors w/hawk HPS pads. From reading the forum the way it faded seemed my problem was boiling fluid. makes sense, I have had the car 4 years and not even opened the brake fluid.
Last month my parking brake lever was coming up too far and not holding the car.

over the weekend I started looking into my issues, found one of the caliper pins in the rear was seized. I freed it up and started to bleed the brakes with Super Blue Fluid. everything was good until I got to the front passenger wheel, the bleeder bolt would not move. Liquid Wrench, Heat, nothing helped, now I have a rounded bleeder.

I packed up, went for a test drive, pedal was not perfect, but better response. Still faded out within a few fast stops. Figured I would take it to a shop to have the bleeding finished. Parking brake works again.
Got home, parked over night, then the problem started with the sinking pedal...:banghead:

Found a bentley online. According to the bentley, manual bleeding on the '03 ABS system should be done in reverse from traditional. Starting at driver front... is this my problem, that I started in the rear?

Things never go right when I touch brakes... with public safety in mind I'll stop working on them

:beer::beer:Thank you for any help:beer::beer:


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## greyhare (Dec 24, 2003)

off the grid said:


> Hey all,
> Car is a '03 Jetta Wagon 1.8T.
> Problem:
> *My pedal is solid at first press and the car stops great, but at a stop the pedal will sink to the floor.* Is this my Master Cylinder? last car I had a master fail had to be pumped and pumped and pumped to stop.
> ...


This is generally a bad master. Did you pump the peddle to bleed? Gunk can build up in the MC, especially when the fluid is too old; when the piston moves past this build up during bleeding it can damage the seal.


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## off the grid (Apr 1, 2008)

Is it 100% necessary to use VAG-Com to bleed the MC?

Thank you


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## greyhare (Dec 24, 2003)

Replacing the master cylinder opens the system up stream of the ABS. It is very difficult to get air out of the ABS without VAG-COM.


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## Rice Rice Baby (Sep 30, 2008)

Sounds like the ABS modulator needs to replace.


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## spitpilot (Feb 14, 2000)

Brakes need maintenance to be reliable and to save you $$$'s in the long term!
Gunk and moisture build up in the fluid...moisture enters through the MC vent hole...mixes with the fluid and settles to the lower parts of the system (water heavier than brake fluid)..you get clogging of ABS valve block and damage to caliper bores. Both of those components cost $$$'s to replace...it's way cheaper to flush fluid like VW requires every two years!
If your car has ABS and you let the MC run dry during fluid flush, or you change MC or anything else upstream from the ABS, or the ABS valve block itself, you will need to "cycle the ABS while bleeding" using a VAG com computer system.:thumbup:


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