I just did the A8 upgrade over the weekend... before I did it my rotors and pads were completely shot and started making a thumping sound when braking. I thought it was just because it was all worn out, maybe the rotor was warped and all. I did the change and the sound is still there, brand new hawk pads and slotted rotors from ecs... any suggestions on what i should be checking? thanks

note, the sounds seems to be coming from the right front.

 

could be a rotor sticking did you lube all the sliding pins?

 

probably one of the 3, control arm (probably an upper), wheel bearing, or cv joint. id say its a control arm though

 

Could it be the abs brakes engaging to early? Can you feel it in the thumping in the brake pedal, and is it pretty loud? On my car the abs sensor timing is off so the abs brakes kick in when there not supposed to, but only during light braking.

 

alright... took the caliper off and inspected everything. I dont think its the abs kicking in, doesnt feel like that. and the sound gets louder and more violent the harder i brake. sounds like something loose or lopsided, i tightened everything and there is a noticeable amount of play in the wheel compared to the other side. the only place it feels loose from is the center bolt holding the hub on... looks like a large hex about a 14mm or so. but the wheel is definitely loose from the center. Does anybody know what size it is?

 

Definitely a wheel bearing then.

 

wheel bearing would cause the thumping sound?

 

Worn control arm bushings could also cause play... But if the wheel bearing housing doesn't move with the wheel then it would definitely be a wheel bearing. However, wheel bearings usually make noise that gets worse as they wear. Though thumping isn't a sound I would generally attribute to wheel bearings.

Has the thumping gotten worse?

 

the thumping is only there under braking and gets worse the harder i brake. do you know what size that hex is? I want to tighten it to see if it makes a difference.

 

They changed that bolt when they switched from ATW to AWM engine codes... If you have ATW then it's a 14mm, if AWM it's 16mm.

Though the axle bolt (I'm assuming that's what this is) only holds the driveshaft into the wheel hub. It would probably have to be really loose for any thumping to occur, and my guess is that thumping would be caused by the passenger-side driveshaft rotating while being compressed.