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I have a 2013 A8L quattro and my warning brake light just came on, I have 65,000 miles on it and I've had it for close to 4 months. How much time do I have until I really need to have my pads replaced and around how much should it cost?
Depends on how you brake. If you are planning to re-use the old rotors, I would say you have one thousand miles to drive and change pads. If you go over this, you risk damage to the rotors. Once you hear grinding, its over, you must purchase new rotors.
When was your last brake job? Have you performed a brake fluid flush yet?
Heck, at three years old Uncle Jim in the front parlor is hardly seasoned. We have posts randomly picked up on D3 or gen 1 Q5 board that go back 10 years occasionally! Anyway, topic has some evergreen value.
As far as actual data, some field data on my S8 with the 400mm rotors. I replaced front pads at 45K miles. first brake job. Sensor light was on. I had already driven it probably 1,000 miles since it went on before I did the brake pads.
1. Obviously at least one sensor in front was blown. I could have broken the other while doing the work, or it may have already been blown too (not sure which side triggered the light originally). Regardless, I found that with time and heat the sensors were harder to remove than expected. I would not count on reusing them, especially if you (like me) have not done the specific job on the vehicle to know how these mount exactly.
2. Pads still had minimum 3mm of life left. New pads measured at 9mm, so light triggers quite early.
3. At full/minimum rotor wear spec on S8, permitted thickness is 3mm less than starting thickness of 38mm. I mic'ed mine at 1.4288" = 36.29mm. Thus, with generally similar wear, across faces, accumulated lip for for sensor being cut by that area was less than one mm per side.
4. The "math" on mine says rotors will drop under spec at approx 75K miles, which is shorter than next incremental 45K miles I got with first set.
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Conclusions:
A. Sensor triggers aggressively early on S8 with OE set up.
B. Lots of pad life still left.
C. Rotor lip was less than a mm of the 3+ mm of pad life.
D. If rotors are not resurfaced--which is a challenge to even get a shop to do with the quasi two piece design--it would theoretically trigger yet earlier on the second pad set. But it seems like it will hit not earlier than about time rotors will go under spec anyway (75K).
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Net: While sort of annoying that sensor goes that prematurely, on my S8 at least in was giving me MANY, MANY thousands of miles of leeway. In addition, given wear spec on rotors, it all sort of fits the old Audi rule of thumb: two sets of pads for every rotor set change. And, it sort of works out even without the background analytics of just letting sensors do their thing, swap out pads at the intermediate change, and do rotors on the second go around.
CAUTION: I would NOT automatically assume these same things for anything but S8 or W12, since they have the Brembo six piston set up, especially around evenness of pad and rotor wear. As in, on the simpler quasi floating/slider set up found on other A8's, my experience is the pad and rotor wear can be less even, particularly from inner edge to outer edge (radially) as far as depth of wear. The sliding set up just has more inherent movement slop in it. Had it on my D3 W12 (385mm rotors), so I saw it with similar twin piston sliding calipers and similar vehicle weight, drivetrain, etc.
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(note on the pad picture: I intentionally pulled pad away from pistons to show the damper pads and mounting; rusty look on pads is only because I hosed area pre job to get rid of extra brake dust)
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Wonderful write-up, as usual, MP. I just didn't want Ober holding his breath for an answer from the OP
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May I add that there is a difference in rotor wear between metallic and ceramic pads (for those who may not know), and with ceramics you may see three sets of pads turned to dust before needing rotors.
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04-13-2022, 08:31 PM
I just didn't want Ober holding his breath for an answer from the OP 
