I could use some help on this one everyone. Been servicing my 2004 A8L for quite a while now but can't figure this one out.

Car has developed a brake pulsation, must prominent when braking hard from high speed. Entire car seems to shudder.

Car has a new set of Michelins on it, there is no vibration up to 90 mph, ride is beautiful and straight.

Shudder started before the new tires, I think after I replaced the rear pads. Since then I have also replaced the rear rotors. The front brakes, pads and rotors were done about 9 months before. I see nothing wrong with the fronts, the rotors do not appear to be warped. I have done nothing to think that they would have warped.

Two things bother me at this point. First, is the shudder seems to be more body related than brake pedal related, the pedal does not seem to be pressing up and down against my foot. Also, on the new rear rotors, they had a protective coating that you are not supposed to remove (I didn't) now after about 15 miles the drivers side rotor is shiny across the entire surface but the passenger side rotor has a 1/4" wide ring where the protective layer is still present, almost as though the pad is not making proper contact. Could be that the protective layer is simply thicker at that point but I thought it was worth noting.

Also when I did the rears it seemed to me that the drivers side rear caliper had a bit more side to side play than the passenger side, but my understanding is that these calipers are supposed to 'float' laterally on the bracket so I didnt think much of it. Am I wrong here, is there something with that rubber boot and 15mm nut assembly that can wear out?

There is no ABS light present, no pad lights present. I used the proper VAGCOM procedure for removing the rear calipers.

I replace most of the front suspension two years ago, with new upper and lower control arm sets and tie rod ends.

Car has 161K on it. 2004 A8L

Any help or even ideas would be great appreciated.

 

Exact same issue with my 2000 A6 Quattro 2.7L 140K. Finding out <4K after purchase that the Dealer's "$1400.00 brake job" was mostly a sales tactic!

Have replaced both rear calipers, pads, Left rear caliper carrier (pins both notably more worn than the right), and the parking brake cables. Had the rotors turned too. None of this has made any difference in the ongoing pulsation--mostly under heavier braking--and all but disappearing under 20 m.p.h.

Would love to hear if anyone out there has experienced the same thing and has a potentially feasible solution--'bout ready to pull my hair out on this--and getting ready to throw in the proverbial towel and take it to a local automotive center that specializes in German cars!

 

Here is a follow up to my situation and some comments on yours.

I fixed my mine by finally pulling off the front calipers and giving them a close inspection. Noticed a small leak in the passenger side so I replaced both, problem solved.

As for your 2000

$1400 for a rear brake job is exactly why I do this stuff myself now. That job takes about an hour and a half. Maybe three to 4 adding in the turn down and e-brake cable. Super easy job to do, and that car doesn't even have the EPB tht you need the VAGCOM for.

I never have rotors turned, just replace them. Even doing this I have returned 2 in 20 years for being out of round. I dont trust them being turned down anymore.

Are you sure on the location of the pulsation. Most braking is done by the front brakes and that is where most of your problems are going to be. Unless you are really sure, drive it, then have someone else drive it and sit in the back and feel it. Also, are you sure its not there at all under 20 or just greatly reduced. Mine was hard to tell.

Are you losing brake fluid at all, even a small amount? This can be hard to tell in the short term because it depends on much hard braking you do and you probably just refilled it with the work done.

I suspect you have a faulty front caliper. With that many miles and the fact your rear pins were worn, I would think a front to back brake replacement isnt out of the question and you are half way there already anyway. Do the fronts yourself for a few hundred and stop feeding the dealers.

 

Thanks for the reply and insight based on your recent experience.

I'll be taking your advice and getting a couple other people to help me test the brakes under different conditions while sitting at different locations in the car. Maybe together we can help localize the worst of the pulsation to one corner.

I've already replaced all that stuff in the back myself. I have no idea what the dealer said was worthy of their $1400--fortunately, I didn't have to pay that as it was supposedly done to the car before I bought it.

Appreciate your reminder of how the front brakes take the brunt of the work and I'll be turning my attention in that direction next week when I get some time off of work. I'll try to remember to post what I find out. I sure haven't noticed any loss of fluid over the past 8 months (and 4K miles) of owning it. Wasn't until very recently that the pulsation began.

Thanks again for your comments!