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mk6 brake pedal goes down when pressed

interweb42

Passed Driver's Ed
2012 MK6 gti with less than 60k miles on it. I recently did a brake job, pads and fluid. Blead system by doing vcd ABS bleed procedure and manual 2 person method for rears.

Pedal feel is good but when I press on the pedal hard and hold down continues to sink like a blead valve is open (won't pump up to firm). When car is off pedal pups up and stays firm. (might go down a bit if I press really hard)

(unsure if it was doing this before brake job)

I Re-checked all the pedal bleed valves and no leaks, fluid level steady in MC. Re-did ABS bleed procedure and issue still exists? :mad0259:

I've read quite a few posts like this and everything seems to point to a defective MC?

Any suggestions would be greatly appreciated

Thanks,

Dan
 

1ashchuckton

Autocross Champion
In my experience what you are seeing is a master cylinder with an internal leak. I haven't had this on my GTI, but have on a few other cars. Time to shop for a new one.
 

interweb42

Passed Driver's Ed
Thanks, I have a new master cylinder on the way plan to install this weekend. Will update!

I feel like if the issue was related to the ABS pump there would be an error code and a brake booster issue would make the brakes really hard to press.
The rate the pedal goes down there would be significant fluid spillage if external leak.

One thing I've been wondering, did over extending the MC damage it? (pressing the pedal all the way to the floor during brake bleeding) I haven't been able to find any definitive info about this online. Should I be using a stop behind the brake pedal when bleeding to prevent this?
 

1ashchuckton

Autocross Champion
I've bled a lot of brakes over the years & never hurt a master cylinder doing so. Although I am relatively new to the GTI. Jay has a lot of experience with these cars so he's the guy who would know for sure.

Also you need to find out what the bench bleeding procedure is for the master, if there is one. I've found not doing a bench bleed can drive you nuts when you try to just bolt it on & bleed on the car.
 

jay745

What Would Glenn Danzig Do
I've bled a lot of brakes over the years & never hurt a master cylinder doing so. Although I am relatively new to the GTI. Jay has a lot of experience with these cars so he's the guy who would know for sure.

Also you need to find out what the bench bleeding procedure is for the master, if there is one. I've found not doing a bench bleed can drive you nuts when you try to just bolt it on & bleed on the car.

Same, never caused damage to the master by pushing the pedal down all the way. To me it sound like you have air in your lines. Bleed all 4 corners the traditional way once more and see if that solves your problem.
 

interweb42

Passed Driver's Ed
Update: So since last time I posted I re-bled the system, tried engaging the ABS system by stopping hard on gravel a few times. Still no change. Also tried running clear line from the front caliper back into the brake fluid reservoir and pumped the pedal for a while...There were no air bubbles in that part of the system.

I was ready to replace the master cylinder but instead of gambling $200 on a part I figured I would take it to the dealership. They did a brake diagnostics and said it just needed to be bled again. They did this with their power bleed system. Issue resolved with the most expensive brake bleed ever right?

Went to pick up the car today same issue. Pedal feel might of been a little bit better. But still when you press down hard on the pedal and hold it, it still continues to go down. After some back and forth with the VW rep (trying the brakes on other cars and him trying to convince me it was the brake booster) I decided to leave it for them to re-check.

At this point I'm leaning towards it being an issue inside the ABS pump... Since there are 2 seals on the master cylinder the chances of them both failing would be slim.

Also, when I did the brake job I did install the Tyrolsport brake caliper stiffening kit, but I see no way that would have anything to do with this issue.
 

interweb42

Passed Driver's Ed
I got a manager involved over the weekend because they once again told me that car stopped fine and it was normal pedal feel.
After some back and forth they finally agreed to re-do the ABS bleed procedure. I picked up the car today.. brake pedal feel is still the same, brakes come on at the correct point and the car stops normally. However if I continue to put pressure on the brake pedal I can push it all the way to the floor.

If I pump the pedal with the car running if will feel like it builds a little pressure but the pedal can still be pushed down to the floor.

If the car is off the pedal will pump up hard. I'm unsure what to do at this point.
 

interweb42

Passed Driver's Ed
I took it to another shop that specialized in repairing euros to have someone else feel the pedal. The guy there confirmed that the pedal definitely feels squishy. He also mentioned that he has seen MC fail when bled the traditional way, being pushed past their normal operating range... but that was on a 100k mile car, mine only has 60k... guess not that far fetched.

I just know I should not be able to push the brake pedal all the way to the floor.
 

Dalew

New member
2012 MK6 gti with less than 60k miles on it. I recently did a brake job, pads and fluid. Blead system by doing vcd ABS bleed procedure and manual 2 person method for rears.

Pedal feel is good but when I press on the pedal hard and hold down continues to sink like a blead valve is open (won't pump up to firm). When car is off pedal pups up and stays firm. (might go down a bit if I press really hard)

(unsure if it was doing this before brake job)

I Re-checked all the pedal bleed valves and no leaks, fluid level steady in MC. Re-did ABS bleed procedure and issue still exists? :mad0259:

I've read quite a few posts like this and everything seems to point to a defective MC?

Any suggestions would be greatly appreciated

Thanks,

Dan
Hi did you ever get to the bottom of this issue as I’m having similar problem been going found in circles for weeks with this on a GOLF MK6 GT TDI I’ve changed rear callipers master cylinder discs and pads on the front I’ve used about 4 gallons of brake fluid used a pressure bleeder and a scanner to activate the abs unit but still my brake pedal is low it works but is low and failed the MOT test because of this
 

This is Ryans face

Not sure if...
I took it to another shop that specialized in repairing euros to have someone else feel the pedal. The guy there confirmed that the pedal definitely feels squishy. He also mentioned that he has seen MC fail when bled the traditional way, being pushed past their normal operating range... but that was on a 100k mile car, mine only has 60k... guess not that far fetched.

I just know I should not be able to push the brake pedal all the way to the floor.
any updates?
 

This is Ryans face

Not sure if...
Hi did you ever get to the bottom of this issue as I’m having similar problem been going found in circles for weeks with this on a GOLF MK6 GT TDI I’ve changed rear callipers master cylinder discs and pads on the front I’ve used about 4 gallons of brake fluid used a pressure bleeder and a scanner to activate the abs unit but still my brake pedal is low it works but is low and failed the MOT test because of this
any updates?
 
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