I did the rear brakes today on the W12. Car has 28,500 miles with original rears. Identical to S8's, and figure it's basically like a 4.2 in back except the rotors are on steroids.

End result:


Picture 1


1. Degree of difficulty: To the post last week about the >$1,000 rear brake job by a dealer, all I can say now is that is really absurd! It was very easy to do. Among the easiest of any car I have seen in the rear. The hardest part by far was simply finding the right part of Bentley to execute the VAG COM command to release the brakes. If I did it without the paint on the new set up, I would say once the wheels are off it would take one hour with experience and decent tools, no more than two hours even with VAG COM and Bentley fumbling and a refreshment break.

2. The basics: it unbolted the normal Audi way for rears. (Note to self--gotta find a thin 17mm wrench like a bike axle cone wrench for holding those caliper pins...) Because of the electronic brake, the time spent running down Bentley was easily made up by avoiding the old having to crank the brake piston back into the caliper like a C4 or 5 or a D2, and of course no climbing under the car to re-tension the parking brake cable like in the old days. All you need to do is use a standard brake caliper piston retractor and push it straight in. Of course what you can't do is clamp it from behind where the delicate parking brake motor gets in the way. Forget the C clamp like I use on many a brake set up; out came the (generic) piston crank-in set I use for Audi's now, but here it just gets pressure applied with no twisting. Really easy.

Pads have no wear sensors, but as I'll cover below, it is calculated by the car separately. Thus, easy again, no wires to undo.

A new one for me compared to other recent Audis--the rotor comes out with no need to remove the carrier bracket. Thus, loosen the set screw, whack the disk a few times with a soft mallet and off it comes. Thus, really easy to do rotors too if it's time for that.

3. Now the not so good sides of what I found:

a. The pad wear was really uneven as between the inside and the outside pads, and the much heavier wear was on the inside pad where you CANNOT see it much at all without the wheel completely off. That was true on both sides of the car, so I would say it is a design problem, not just some single caliper fluke or faulty factory installation. New pads are 10mm thick in the rear. The outside ones were 6 ½ and 7 mm, while in inner ones were about 4mm. That is a BIG percentage spread, and until I saw this I had actually figured the rear pads still had a lot of life by periodic inspections through the wheels seeing the outer pads. Wrong. Here is a picture of the four pads I pulled out. If you look carefully, the difference in thickness is pretty evident. The two thinner ones were on the inside.


Picture 2


If you look at the numbers, the inners were wearing at almost twice the rate as the outers. That's not good. Of course both the piston and the parking brake operate from the inside which would start to explain it. But, that shouldn't happen. Needless to say, I carefully greased the floating caliper pins as well as the pad contact points with the spring clips. Disappointing the much greater wear is on the hidden pad.

When I went to reset the pad wear in VAGCOM, it told me the car thought the rears were down to 3mm. So the one better news item here is somehow it decided the wear was a bit worse than the thinnest pad. How it got there I'm not sure since you would think it would look at the parking brake total travel over time, which would involve an average of both inner and outer pad wear. Quick math says using the most worn pad, it would get to metal by 47,500 total miles. Assuming the pads started at 10mm and it calculates linearly, the car would conclude it got to metal just past 40,000 miles

b. As I pulled the pads out, one of the vibration dampeners just fell off the pad on the left side. They are supposed to be riveted or spot welded on, so this was a failure. It's obvious in this picture:


Picture 3

This may explain finally why I had a bit of chatter on a slow stop the first time or so in the morning as the brakes got a bit of heat. In the details of Picture 3 you can see some letters and a number at the bottom of the pad on the left, starting with "FER". Thus I'm guessing the OEM supplier is Ferrodo, which I have come across on some prior Audis. The EBC's I replaced them with had a stick on anti vibration pad that locks into some distinct dimples in the pad backing.

c. Finally, the rotors. Okay, it's a W12 so it is somewhat heavier and gets up and goes and then stops maybe a step or two more lively than a 4.2 in everyday use. But the rotors are also sized up over the 4.2. Bigger (335mm) than the front rotors on my C5 4.2 even, which itself has strong brakes! The caliper unit is basically the same as the D3 4.2 I think, and the overall rear set up is quite similar to the C5 RS6. So, what's all this mean for the rotor? The new rotor spec is 22mm per (erroneous) Bentley, but both the new and old rotor (the old one at the outer edge) spec at 23.2mm (.915"). The wear limit nets to 20mm (.787") per the rotor stamping ). Bentley says 2 mm off of what they think is a 22mm rotor that also gets to 20mm. Well, I mic'ed the rotors I pulled off--which were in good condition. Min on one was .857", while on the other it was .854". Variance anywhere on the rotor was .003" or less, and visually the wear looks quite even and clean. You can see some of the rotor in the background of Picture 3 just above. Thus, rotor wear to date at 28,500 miles is .061" or 1.5 mm. That yields a life expectancy of about 2.1 of my current odometer reading, or about 60,000 miles. That does not agree with my prior Audi experience, which is basically I don't need to change rear rotors except for a brake job at over 100K miles or if they get quite scored somehow. Seems more like the minimum life of a front rotor driven somewhat hard to me, assuming it doesn't warp. Of course if the rotor had started at 22mm the math would be a lot different--it would run 5x my current mileage, but I can tell from the inner and outer lips it plainly started thicker than that.

Net--note to self and the board--these things wear rear rotors and pads a lot more than I would have thought. I figured the basic upsizing of the brakes took care of the added power and weight to net the wear about the same. Brakes perform great in the field, but the OEM pad situation and wear isn't up to what I would have expected.

4. New set up: EBC red pads, a careful home paint job with high temp brake paint from a rattle can, and the drilled and slotted OEM spec rotors (about the only aftermarket ones available besides straight OEM).

a. EBC Reds are ceramics, number DP31470C, aka standard brake pad code D1018. Box says they are for (C5) RS6's and Phaetons. Backing shape is identical to the OEM pads. They have a center slot cut in the pad, maybe for outgassing. The outer edge of the pad is the same width as the OEMs, but the inner edge nearest the hub tapers down quite a bit more. Swept area would be the same, but it looks like somewhat less pad material actually than the OEM set is touching the pad toward the inner part of the rotor. A picture of old vs. new rotors and pads:


Picture 4

b. Paint was spray on VHT brake caliper enamel in cast aluminum and black. I sprayed the calipers on the car with some basic tape masking and without undoing the brake lines. I had sprayed them with brake cleaner with some rag and brush work, and touched up the seam marks with a flat file. Oh yeah, truth be known I Dremeled out the VW logo on the caliper, leaving just the four rings logo cast into the metal (see the blank area above the four rings in Picture 6), plus the TRW markings to the left. The calipers dried overnight and I gave them one quick sanding between coats, just on the most visible areas. I removed the caliper brackets from the car, flat filed and Dremeled the obvious seams visible from the wheel side, especially the forward face where I put the decal. I masked all the bare metal areas (this and sanding were the longest steps; about an hour each), and gave them several coats before oven curing them, then sanded them and repainted. Drying time basically took off and on for a day+. Decal is from Xenonmods with a clear coat on top. From test experience the VHT clearcoat turns yellow at higher temps, so I went with a red decal instead of silver (that would end up gold if it yellowed), and I applied the clearcoat after I bolted the bracket back up, choosing not to go to the 350 degree oven cook. Last time I turned a front brake part with clearcoat yellow at about 400 degrees over about an hour. The silver paint and black paint hold up perfectly at those temps and even up to a sustained 450-500 degrees in the oven, and when baked get nice and hard.

c. The brake rotors are the supposed Disc Italia rotors from Brakeworld, which are really just machined OEM rotors (complete with laser engraved Audi part number). Goes with the fronts I did previously--the link to the front install is in my auto sig below. I'm catching up with E/CovertW12 who already has done the same in back.


This one shows the laser engraving on the OEM rotor, plus the 20MM H&R DRA spacer I use in the rear; I tweaked the image in Photoshop to bring out the markings and edges better; in real life the calipers look much smoother and the cooling fins look normal OEM rather than rough as they do here.


Picture 5


Another angle (pre-spacer):


Picture 6


Another angle all back together:


Picture 7

....

Current #1: '06 D3 A8L W12 brilliant black w/ amaretto & 4 seat setup, GmbH custom, CPO; modestly VAG COM lowered, H&R 20mm rear DRA's with 275/35 on OEM polished + forged 20's; S8 sway bars (see: rear bar and gen'l D3 bar info and front bar); tweaked 385mm front factory brake mod and matching rear brake mod; matching C6 A6 back headrests (better rear view: headrest tweak); owner installed AMI retrofit with part number details here; other VAG COM tweaking to suit
Current #2. C5 '00 A6 4.2 ming blue w/ beige, new off showroom floor; Lemiwinks + VAG COM tweaks; smoked tails; RS 6 OEM 18's; RNS-D (CD) Navi
Prior: '96 C4 A6 2.8Q, still w/ family; '85 C3 5000S 5 sp FWD, '73 C1 100LS

helpful cross reference to a C6 post with MMI and other TSB's that also cover D3 A8's.