Owners1

Hello,

I am posting this because I am not sure what brakes look like when they are good or bad. The mechanic working on my A8 has told me that the rotors need to be replaced as well as the pads.

I have 39,000 miles right now and I have included pictures of the front brakes.

Any help would be appreciated. Thanks

the_duke

The only way to know for sure would be to measure the thickness.

jeneag

May or may not work: slide your finger between main area of the rotor and the edge, sometimes (depends on the pads) edge will be higher than main area. As far as pads it's hard know w/o disassembling them i think.. maybe there is special tools, i dunno. From the picture it looks like you have some headroom but hard to tell and depends on your driving style.

MP4.2+6.0

+1.

Not as scientifically, but most rotors have an edge lip from wear. If that lip is more than about 1-1.5 mm, they are done. Call that 1/16" approx. at about 1.5mm. Wear will normally be symmetrical on other side, so you double it as far as comparing to spec. Many rotor specs are only 2mm now, though thicker fronts often spec out at 3mm. The specific wear limit is laser etched on the rotor hat area IIRC.

Old rule of thumb for most Audi's (and many others) is they could run a second set of pads on a given set of rotors. What I found and did on my D3, and C5 4.2 before that. But some owners of Audis with the lighter weight quasi two piece rotors like found on the D4's seem to report more wear. The longest running ones with these types of rotors seen in U.S. are R8's, RS4s and RS5's, so not exactly a great sample set for longer wear given driver profiles--putting aside a big percentage of R8's are also quasi garage queens at low miles. Dealers also often try to say a new set of rotors is needed every time, and if cornered on a wear measurement then may say it could go below spec during life of next pad set. Up to you, but unless I am down very close to the min. spec at a change/inspection point, I do pads only. Frankly unless it is Autobahn conditions for which the brake set up is spec'ed/based, most drivers don't work the brakes hard on a sustained basis and traction/ABS is almost always the limiting factor.

Garycw

Id just have them turned. And replace your pads next tine before they're worn so much. Don't fall for the new calipers either unless it can be proven beyond dought ones sticking. With those miles should Only need pads and replace next time 30-35k mi depending on driving habits. I try to avoid hard stops as much as possible. If you know you're going to be stopping ahead of time, get Off the gas. I even use the paddle shifter occasionally but don't make a habit of it

MP4.2+6.0

May also find shops don't want to turn the quasi two piece type rotors the car has. The rings are permanently mounted on pins to the center hat, so are pretty unique. From a friend I was helping with a brake job on a prior gen M6 that had an early implementation of them, the local shops would not turn them. Underlying supplier also keeps an extremely low profile and apparently supplies them only to the manufacturers. Or, maybe licenses them or is precluded contractually or output wise from selling into channels?

Seems seems to be an assumption these rotors are same old thing, but they are unusual, typically without other non OE suppliers, and not what machine shops are used to or know. The calipers are more conventional, though of course in the larger 4.0/S8/W12 size a pretty full on Brembo implementation.

the_duke

Why turn them at all if they are not warped? I usually just hit them with a small sanding disc attachment I have for my drill just to take the glaze off and then make sure they are clean.

If they look like the picture below you've waited too long to change them.

vtraudt

Replaced pads at 70k (close to wear mark). Front and rear.
Very smooth rotors, no grooves. Just turned them.
Caliper pistons moved smooth and easy.

Now brakes feel soft, low initial bite. Appear to need longer pedal travel for same stopping power. Even after 100 easy miles to wear them in.
Full force braking generates good stopping power.

Brake fluid was full.
Flushed a cup of brake fluid out of front brakes (in case air got in for some reason; but clearly symptoms do NOT feel like air in lines). No change.

Anybody running Bosch pads?
If not pad material, what else could be the cause?

the_duke

You don't mention what vehicle we're talking about so it's tough to say. My guess is that it's the pads.

vtraudt

Didn't know that there are lot of variations in the D4 A8 platform.
This is a 2011 A8L.
BTW: the Bosch pads did NOT come with pad wear sensors!