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  1. #1
    Established Member Two Rings
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    Intermittent long travel in brake pedal. Possible causes?

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    For a while now I have been experiencing this occasional long travel in my brake pedal. What I mean by that is sometimes it feels like depressing the brake pedal doesn't do anything until it is nearly to the floor. It usually only happens when I am driving at moderate speeds around town and only when I am depressing the pedal very gradually, like when coming up on a stop sign, or preparing to make a turn. When I feel that that empty feeling in the brake pedal I just pump it once and that is usually enough to bring it back to normal.

    I just bled the brakes and that didn't do anything. Anybody have any thoughts? Could this be caliper related? Master cylinder? Any input would be appreciated. I am running B6 S4 brakes all around and have been for about 5 years or so. I've had this brake issue for almost 2 years now. It has never gotten any worse or better so I didn't worry about it. Plus my audi isn't my DD anymore, but I'd like to get it resolved.

  2. #2
    Veteran Member Four Rings old guy's Avatar
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    If a pump of the pedal brings it back up It sure sounds like you have worn seals in the master cylinder.

  3. #3
    Veteran Member Four Rings DownhillA4's Avatar
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    Vlad, i've noticed this as well. Only started right after I installed B6 S4 rears. Have zero air in my lines since I bled the brakes a few times to verify. Not sure what it could be. Then again, upon installing the B6 S4 rears the car hasn't gone further than the driveway but the pedal definately feels mushier then before the install.
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  4. #4
    Established Member Two Rings
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    Quote Originally Posted by DownhillA4 View Post
    Vlad, i've noticed this as well. Only started right after I installed B6 S4 rears. Have zero air in my lines since I bled the brakes a few times to verify. Not sure what it could be. Then again, upon installing the B6 S4 rears the car hasn't gone further than the driveway but the pedal definately feels mushier then before the install.
    Hmm well from my experience just switching to S4 brakes wouldn't cause it necessarily. When I upgraded, my pedal was solid as a rock for years. I suspect there is something else going on here.

  5. #5
    Established Member Two Rings
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    Quote Originally Posted by old guy View Post
    If a pump of the pedal brings it back up It sure sounds like you have worn seals in the master cylinder.
    Interesting, thanks for the input. I don't know about the entire braking system to understand quite how to make that connection. I'll have to do some reading. Any chance you can elaborate a little about how you came to that conclusion?

  6. #6
    Veteran Member Four Rings lookaught's Avatar
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    Quote Originally Posted by vlad View Post
    Interesting, thanks for the input. I don't know about the entire braking system to understand quite how to make that connection. I'll have to do some reading. Any chance you can elaborate a little about how you came to that conclusion?
    When you push the brake pedal and it keeps on moving that means that fluid is still moving as well. If you aren't losing fluid (no leaks?), but the pedal still moves, that means when you push the pedal the piston that is supposed to transfer the fluid down the lines is not doing it's job. When the MC piston leaks the fluid doesn't leak out of the car, it just stays put in the MC (or goes back up a bit).

    I would look all over for leaks very carefully and then by elimination replace the MC. It makes sense that it does this when slowly applying brake pressure, allowing time for the fluid to escape, as opposed to a hard stop that is abrupt and only a fraction leaks past.

    There are a number of B6 cars being parted out in the vortex classifies, I'll bet you can get a used MC for a good price.
    Jon

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  7. #7
    Established Member Two Rings
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    Quote Originally Posted by lookaught View Post
    When you push the brake pedal and it keeps on moving that means that fluid is still moving as well. If you aren't losing fluid (no leaks?), but the pedal still moves, that means when you push the pedal the piston that is supposed to transfer the fluid down the lines is not doing it's job. When the MC piston leaks the fluid doesn't leak out of the car, it just stays put in the MC (or goes back up a bit).

    I would look all over for leaks very carefully and then by elimination replace the MC. It makes sense that it does this when slowly applying brake pressure, allowing time for the fluid to escape, as opposed to a hard stop that is abrupt and only a fraction leaks past.

    There are a number of B6 cars being parted out in the vortex classifies, I'll bet you can get a used MC for a good price.
    Got it, thanks for that explanation. I'm pretty confident there are no leaks that would allow fluid out of the system. I just bled the brakes last weekend for the first time in quite a while and I didn't have to ever top off the brake fluid prior to that. Sounds MC is a strong contender. Assuming I can get one at a decent price, how difficult is it to replace?

  8. #8
    Veteran Member Four Rings lookaught's Avatar
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    I've never done one on a B6, but google is your friend:

    http://www.audizine.com/forum/showth...er-removal-DIY

    Looks easy enough, though any work that involves laying on your back under the steering wheel is awkward and back pain inducing. I recommend buying a set of flare wrenches for the brake line fittings. I think I bought gearwrench flex head wrenches in a set on amazon for like $40 a while back. Solid investment. Good luck.
    Jon

    WTB 1.8t cylinder honing brush - PM me if you have one!

    go > show


    Ich liebe mein Audi!

    2002 GTRS Avant - Built with love, sweat, bloody knuckles, and pride.

  9. #9
    Established Member Two Rings
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    Quote Originally Posted by lookaught View Post
    I've never done one on a B6, but google is your friend:

    http://www.audizine.com/forum/showth...er-removal-DIY

    Looks easy enough, though any work that involves laying on your back under the steering wheel is awkward and back pain inducing. I recommend buying a set of flare wrenches for the brake line fittings. I think I bought gearwrench flex head wrenches in a set on amazon for like $40 a while back. Solid investment. Good luck.
    Yeah I saw that post, I just have a hard time getting a feel for how much work that would be from just a written description.

    Definitely seems like the master cylinder I guess. With the car on, I can gradually depress the brake pedal all the way to the floor without any resistance. If fluid isn't leaking out of the system amywhere, seems like it must be a problem with the MC yeah?

  10. #10
    Veteran Member Four Rings old guy's Avatar
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    Yep. The master cylinder piston has two seals. The primary seal provides the pressure to activate the brakes. When the primary seal starts to leak the fluid going past the primary seal gets pushed back into the brake fluid reservoir by the secondary seal. That's why you lose braking power but the fluid level remains the same.

  11. #11
    Veteran Member Four Rings lookaught's Avatar
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    Quote Originally Posted by vlad View Post
    Yeah I saw that post, I just have a hard time getting a feel for how much work that would be from just a written description.

    Definitely seems like the master cylinder I guess. With the car on, I can gradually depress the brake pedal all the way to the floor without any resistance. If fluid isn't leaking out of the system amywhere, seems like it must be a problem with the MC yeah?
    I like to refer to a job like that as:

    A saturday afternoon and a six pack.
    Jon

    WTB 1.8t cylinder honing brush - PM me if you have one!

    go > show


    Ich liebe mein Audi!

    2002 GTRS Avant - Built with love, sweat, bloody knuckles, and pride.



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