tadslc

A little history - Just got finished replacing both the front a rear brake pads (stock Audi pads) on my Dad’s 2007 A8. Had the rotors turned as well. Have Vag-Com to reset the parking brake, no problem there.

Problem, BIG problem – I happily get everything done and hand the keys to my Dad. He drives off but returns a minute later saying the brakes are shuddering / pulsing. I get in the driver’s seat and take it for a spin. To my horror, the brakes and shuddering / pulsing really, really bad. Feel it through the pedal like the ABS is kicking in and out. It’s like nothing I’ve ever experienced after a brake job. I’m no professional but I’ve done dozens in my lifetime.

Hooked the Vag-Com back up and didn’t get any codes.

Anyone have any ideas? My initial impression was warped rotors but my goodness This is bad, the car is undrivable!

Thanks,
Tad

Mister Bally

I'd try a really, really hard brake application in case one pad is crooked in it's carrier. However, a hard application could break a crooked pad if it doesn't properly seat itself.

You'll need need to determine if the problem is the front or the rears. Very difficult to do with the electric rear parking brakes. Alas, drive and apply the parking brake. You'll have to try a couple of times as it has a safety program to delay the application in a moving vehicle. If applying the rear parking brake causes the shudder/pulsing, the rears are where you look. If no shuddering from the parking (rear) brake, yet when you press the pedal they shudder, look at the fronts.

tadslc

Good idea, I'll try it in the AM, the cars at my office.

MP4.2+6.0

while in motion is really going to be a lot more than you might expect--much more than the old pull the handle up type Audi marginal increase in stopping.

Yes, check pad seating.

Make sure pads are bedded--5-10 stops from speed.

Make sure lug bolts are all tight (if not both wheel and rotor could be wobbling).

Make sure carrier bolts for calipers are bolted down.

Make sure ABS sensors didn't get screwed up or out of position (though it doesn't sound like ABS is actually kicking in from whay you seem to describe).

After that, it comes back to one off/odd stuff to hard to figure out without seeing it, or the basic possible warped rotor somewhere.

tadslc

I just finished inspecting all pads, carriers, etc. and everything seems in good order.

Drove the car, same symptoms as before. Severe shuddering coming up thru the brake pedal at low speeds on up.

I swear it feels like an ABS problem.

At a fairly low speed, I activated the emergency brake and the severe shuddering was present.

I tried to recheck everything with the Vag-Com and now the low brake pad light is on even though in Adaptation group 006 shows 14. Working on fixing that now.

Any other advice?

Mister Bally

You metioned using the software and interface to "reset" the parking brake in the rear. You did two different things: 1. Backed off the pistons electronically to remove and then install new pads. and
2. measured new pad thickness to set the pistons correctly.

This is what you did, correct? You did not use a tool or C-clamp to press the rear caliper pistons in, correct?

If you did force the rear pison(s) in, all bets are off. Otherwise, I'm stumped based on all given information.

tadslc

i did use the software to back off the EPB but when I went to remove the calipers, the pistons still had to be pushed in some manually.

I installed the new pads (OEM Audi)after measuring their thickness. put this into the adaptation group 006, closed the pistons with Vag-Com and ran them through the test cycle.

tadslc

I think I might have found the problem.

I measured the disc run-out and it measured 12-14 mils. I think stock they should be 1-2 mils. I read somewhere you can start to feel 4 mils. A severely wrapped rotor would be 7-8 mils.

Just a ****ty job of turning the rotors. I won't use that company again.

I never did find any Audi specs though for this. Anyone know Audi's tolerences for this?


Tad

tadslc

Rotors replaced, problem still there.

It's got to be an ABS problem but how?

Any suggestions?


Thanks

PAC

possibly flush/bleed the brake lines. run a vag check on the ABS, operating it.