I am doing a brakepad replacement on my VDP. It has been somewhat slow to stop and that makes me nervous. I thought some new brake pads might help. The pedal is not spongy like when it needs bleeding.. It has a hard pedal, but the car just doesn't stop as quickly as it should. All the rotors are smooth, but all are black. Brake Clean removes some of the black, but it takes 400 grit sandpaper to cut through along with a lot of time and elbow grease. The pads are 50% and look OK to me. I am really not familiar enough with this car to judge, but on my Jeep the rotors are bare metal where the pads ride.I dont know what this black stuff is that coats the rotor and is this the cause of the poor stopping?. I don't see any black material on the pads and they are very hard with nothing that can be rubbed off. Is the black something that is from the facory like a metal coating? I can put up a picture but it just shows a black rotor!

 

When was the last time you flushed and bled in new fluid and rebuilt the calipers? Brake fluid is corrosive and creates residue in the lines and can prevent the pistons from functioning properly. As for the black residue, that could be from a stuck caliper (guide pins or pistons)...what kind of wear are on the pads.
Pics would be helpful,..you don't need to take a shot right on the rotor, take them from a couple feet back and you can adjust it later using Microsoft Paint or other program.

 

Black stuff ? Lot's of brake dust ? Sticking brakes ? and therefore pads overheats and gets hard and shiny and after that you will need more brake force to stop.

 

I have never seen a black brake rotor, they should be bare metal and at least somewhat silvery. Definitely want pics please.

Maybe pads and rotors. Bet the braking difference is significant.