I have a 2.7T 6sp and it has always had a strange groaning noise when I brake hard at high-ish speeds. The car shakes a bit, the shifter moves around more than I would expect.

I always thought it was the rear brakes because the car had been stored for a few months before I bought it and it had pad marks on the rotors from where the parking brake had been on. Yesterday I put new rotors and pads on the rear and much to my dismay I still have the same problem. I guess it could be the front brakes, but the vibration feels like it comes from the middle to rear of the car, nothing can be felt through the steering wheel. I know how warped rotors feel and this is a higher frequency vibration and only happens at higher speeds.

Any ideas?

Thanks!

 

ABS, It will actuate the brakes so fast to keep you from skidding it sounds like a groan.(as in - ententententent) Furthermore if your wheel sensors are shot it will do it more frequently. But at high speeds and hard braking or slippery surfaces that is when it supposed to happen.

 

Good guess, but I'm not that heavy on the brakes! This is more 'moderate' braking I guess, nothing unusual. I could unplug the ABS controller just for fun and see if it makes any difference I guess. Doesn't the light flicker when ABS kicks in?

 

You don't have to be if you roll over sand and one tire slips just a little the sensors will pick it up and activate the ABS. It happens to me sometimes (Alot of sand here in SW FL)

 

put some brake oil. it will surely work properly

 

Should I apply the oil directly to the rotors or on the pad surfaces and let it wipe onto the rotors? Any particular oil, or will used motor oil work OK?

 

Never "oil" the brakes. In spite of your disclaimer about warped rotors, they could be slightly warped in the front or you could have a sticking caliper. Since you seem to know brakes, it may be worth taking them apart, cleaning and checking. I suppose a malfunctioning ABS could also be the culprit. I assume the problem does not occur if you coast (engine brake), rather than brake, to slow down?

 

Sorry, that was my attempt at sarcasm - wife says I should stop it because not many people get it in the US. My humour was fine-tuned in Britain and is hard to change.

Under engine braking everything is smooth. At lower speeds there is no sign of anything strange going on. When it does occur, nothing can be felt through the wheel, and the shifter wobbles excitedly which makes me think it must be the rear end. These are brand new rotors and pads on the rear, the pistons retracted as they should with no fight, the pins are lubed with high temp grease and float easily. Maybe I have a bad wheel bearing? I can't hear it when driving but then the A6 is pretty well insulated. I've had bearings fail on plenty of other cars though and it is pretty easy to notice. Very strange....

 

Were you able to find what the issue was with you braking? I am having some serious shaking when braking in the front and it sounds very much like what you experienced. New Pad's and rotors made no difference. Auto shops see nothing loose or worn on the suspension. Was thinking maybe stuck caliper, since it is a two piston set up, even though both of them appear to move freely. possible bearing, just does not seem likely? possible ABS issues, I suppose it could affect it at all speeds. I just thought that it only kicked in at hard braking not the full range of braking. Really need to figure this out, any help is appreciated.

 

Worn caliper guiding pins could be a reason for vibration.