I put a new master cylinder in my 01 A6 4.2, and the brakes still go to the floor. Even when I pump them they don't get firm. I bench bled the cylinder. Any ideas would help.

 

nobody has any ideas.

 

Unless you have the misfortune of buying a defective master cylinder, I can only think of a fluid leak or an air in the system. The former should be easy to spot. For the second, try bleeding them again. My only other thought is that maybe something mechanical is broken: i.e., the physical connection from the brake pedal to the master cylinder.

 

Did you use a VAG-COM and bleed the ABS system? AFAIK the normal bleeding of the brakes does not properly remove all of the air from the ABS pump/valve body. There is a procedure involving a VAG-COM to fully bleed the ABS.

 

Once the hydraulic system is full of fluid, a push on the brakes should get firm. Unless something mechanical in the cylinder is broken. Otherwise, I would point to air being allowed into the lines somehow when the cylinder was replaced. Have you bled each wheel?