I changed my front pads and rotors today on my 98 a4 2.8 quattro. I am going to be changing the rears tomorrow. I put drilled rotors on the front and new pads. During the change I had an issue with the front passenger side brake caliper piston popping all the way out of its boot and I got all sorts of air in the lines and had to bleed the brakes after I successfully put the piston back into its boot and compressed it. After i was done bleeding the brakes I took the car for a spin to break the brakes in. I was going to make 8 fast complete stops at 30-35mph and then 2 at 40-45mph. Everything was going fine until my 5th stop and right before the car came to a rest there was a loud knock noise that was also felt in the pedal and the ABS light came on along with the brake light blinking and 3 beeps then turned off. The car brakes fine until right before it comes to a complete rest and then it makes that knock sound but the lights don't always flash. The lights flashed one other time on my way home from the break in after the initial issue but I wasn't breaking... I was having the ABS/brake light flash and 3 beeps randomly before I changed my brakes but it was just random occasions. I am very worried about the knock that happens though. PLEASE SOMEONE HELP ME ASAP! I wont be able to sleep until I get this figured out!

 

chec kthe ABS seonsors they get pushed in until they tocuh the hub then pull them back 1mm or so. Also make sure your pads are in correctly they might be off.

 

What does the abs sensor look like exactly? I have noticed the front passenger wheel well smoking while sitting at a stop some times. Thats the same side the piston popped out of the caliber. Could it be that the rubber gromet around the piston got a small hole in it somehow and brake fluid is burning every now and again? If you have a pic where you can point out the abs sensor that would be awesome! Thanks for the help so far

 

Try searching te forum for the pic. But the clunking sounds like a loose caliper or pad to me.

 

the only reason i said ABS was because of the light flashing. Id agree with lose pad not "clipped" in correctly. The ABS seonsor will be comming from the spindle and will have a wire going up the spindle into the wheel well.