TimZ

Hey guys - 2002 S6 Avant - All of a sudden I have to push quite a bit further down on the brake pedal to brake. They seem to go back to normal pressure sometimes, just to go back to having to press further down on the pedal to brake. My indy mechanic says they get the same feeling so its not just me but they can't find anything wrong whatsoever. Any help is much appreciated. Brakes are stock expect for Hawk HPS street pads.
Thanks!
Tim

2.7Lturbo

check your fluid levels?

TimZ

Yep fluid level is fine. I checked that before taking it to the shop. They've looked it over completely and found nothing. They're waiting on my word to dive further into it.

Just Me

you either have air that's moving around, or an intermittent, failing master cylinder, IMO.

Intermittent problems are the most frustrating.

Good luck, report back.

G

towertro11

You can try to pinpoint the problem by performing a few quick tests.

When does the pedal lose pressure? When driving, after highway, on startup?

How does the pedal recover pressure? Additional pumping, after sitting, after driving, at high rpm?

Things in my experience (not audi) that can cause these types of symptoms:

Air or water in the lines, failing master cylinder, brake booster problems, hanging caliper overheating the brake fluid.

Simplest first step would be to bleed the brakes and see if the problem recurs. Should be fairly inexpensive as well. I would hope that a mechanic would be able to detect a hanging caliper, so that should be low on the list, but also easy to diagnose yourself.

Good luck.
John

TimZ

Thanks guys! I'm having them bleed the lines now and see what happens. Hopefully that takes care of it. I'll keep you posted.
Tim

TimZ

Turns out it's the master cylinder. My mechanic had trouble removing it. Said he would of had to cut some aluminum near the firewall to get it out. He's researching how to properly take it out. Anyone know the answer to this one? He said possibly removing the brake booster would do it but still isn't sure there'd be enough room.
Thanks for any help!

sootwagen

From the Audi A6 Service Manual 1998-2004 (A6, S6, Allroad Quattro, RS6), section 47-8:

Pull off rubber molding at engine compartment rear bulkhead. Pull plenum chamber cover forward and remove.

Unscrew brake fluid reservoir cap and siphon out as much fluid as possible from fluid reservoir.

- Manual transmission vehicle: Disconnect clutch master cylinder supply hose and seal with plug.

Disconnect brake fluid level warning switch harness connector.

Working below brake fluid reservoir:

Disconnect brake lines at brake master cylinder. Immediately seal brake lines and plug brake fluid ports.

Remove brake master cylinder M16 mounting nuts.

Carefully remove brake master cylinder from brake booster.

I didn't see anything in the procedure regarding the removal of anything else to get at the master cylinder.

TimZ

Thanks I'll forward this to my mechanic. He's done the master cylinder swap on many A6's including 2002's with the 4.2. He says the S6 is just different and getting it out of there seems impossible without modifications. Thanks for posting this tho!
Tim

TimZ

New master cylinder installed, flushed the brake lines, mechanic says everything looks perfect, but the pedal still feels off. Same thing. Sometimes theres the correct amount of pressure when I press the pedal (pedal goes in the amount I'm used to) and sometimes I have to press the pedal further down to brake. What else could this be? Any further help is much appreciated!
Tim