aebarto11

I've been fighting this issue now for several months and can't seem to get it lined out. It all began when I started hearing what sounded like a pad was dragging ever so slightly. I could faintly hear it when coming to a complete stop. It wasn't bad - just a sign to me that it was probably time to re-build the calipers. Shortly after this discovery - I started noticing uneven wear marks on the front left rotor where the sound was coming from. I also noticed a few minor discrepancies on the front right as well. Seeing this convinced me a little more that a caliper rebuild and flush would probably get me back on track. When I finally got a free weekend - I pulled the calipers and started the re-build.

Front Calipers:
I put all new seals and guide pins throughout. The pistons all looked great and none of the seals were breached. I cleaned everything up installed new pads, greased the pins, & re-installed the rotors. I had the front rotors turned so I could start this process with a true-surfaced rotor. The shop that turned the rotors did end up taking some material off, but left me still within tolerance.

Rear Calipers:
I put all new seals and guide pins throughout. The rear pistons were also fine - however the seals on both rears had small tears, but I didn't see any issues from it. I cleaned everything up and installed new rotors and pads.

After the re-build - I did a complete flush using a Motive pressure bleeder (highly recommend owning one of these), buttoned everything back up and tested. Everything seemed back to normal - no noises what so ever and steering wheel felt rock solid and smooth. A couple weeks later - the same slight dragging noise came back and I could start to see lines in the rotor and slight uneven wear again. That weekend I pulled the calipers again to make sure nothing was getting hung up and the pads were seated correctly. Everything looked fine and the pins were free to move. I pressed the pistons a tad and re-assembled. I also worked the rotor surface a little with sandpaper to remove the wear marks. The car drove fine again after that - no noise. A few more weeks go by and this time I'm heading home from a business trip I drove to. I put about 600 miles on the car altogether that week. I started hearing the noise again! When I got home, I looked at the calipers and the same marks were there - again! I noted in the picture about the drivers side rotor lines - the picture makes them look like they're deep, but they're barely below the surface. I checked the pads and I couldn't see anything embedded that would cause the marks (at least from what I can see and feel.) Again - these are new pads making the same marks as the previous ones!


Driver's side front - where noise seems to be coming from. The groves look worse in picture - you can barely feel them with your finger nail.

Passenger side front.

I thought about the front left rotor being bad, but the passenger side is getting uneven wear too? I also considered the calipers themselves as being the culprit although they looked and acted fine during the rebuild? Fluid is new and the brakes are stopping like they should. The only issues are the slight dragging noise at coasting speeds and the visible pad wear issues. I didn't replace the flex lines going to the calipers during the re-build, but the fluid seemed to flow fine during the flush. At this point all I know to do is throw money and parts at it till it's fixed, which I definitely want to avoid - I'm out of ideas!

MP4.2+6.0

Try replacing the front bushings on which the calipers float relative to the pins. You can get them from the dealer for a lot more bucks, or from rockauto.com in the jobber type brands for about $5 for a set. Now that I know they are available, I do those regular course. I think they help the caliper stay true to the rotor rather than shifting around or maybe twisting torsionally to a greater extent.

They have the rear boot kits for all of $3 for the set too. Having bought both types of parts from Audi and the rockauto jobber type, honestly you can't tell the difference side by side.

aebarto11

I forgot to mention that I replaced those as well during the caliper rebuild including the guide pins. I was pretty sure they were the culprit at the beginning. Surprisingly the bushings I removed looked fine, but I replaced them anyways. Maybe I didn't grease the new ones enough after re-install. I was always taught not to grease them a ton - just enough to allow for proper movement. The rear calipers moved extremely easily - should the fronts be close to the same? My fronts did take a little effort to slide back and forth?

MP4.2+6.0

My fronts were fairly stiff to move w/ new bushings. Just driving will tend to back the pistons off ever so slightly as he rotors spin to reduce the drag on the rotor. The wear marks on your driver's side front could be as simple as a pice of grit either in the pad material or that got in there somehow. But you say you checked the pads too, so not sure. If you have a IR temperature gun, you could check the caliper temp on the two sides. Front to rear will vary, but side to side should be pretty close after some decent stops. You could also bed the pads in again, whether at same time or otherwise.

FWIW, I did have a 2000 C5 A6 4.2 rear caliper quasi lock up on me. Design of the rear calipers has been about the same like forever now, just with the electric parking brake grafted on with D3. I noticed it just feeling like car was a little sluggish after already changing rear pads from early wear. Then I stopped for gas and realized how hot the right rear rotor was by the fill door. Got one of EBay and problem solved. Earlier step on yours would the IR gun to see if you pick unusual side to side temperature differences suggesting something is dragging. Even older story BTW was on C3 Audi 5000 was I would suddenly have brakes drag so much I had to pull over. Before long I realized master cylinder was freezing up when car got hot. I found it when I rapped on it with a piece of wood (later a rubber mallet) and it freed up. Audi's still have the dual diagonal brake line set up even with ABS, so if you find both one front and one rear caliper are hot it a diagonal pattern, think master cylinder.