Had the same problem on mine. After the dealer replaced the front wheel bearings on the car, it had a terrible vibration/shudder when I braked. Took it back and they said it was grease on the brake pads. Eventually found out that they didn't put the discs back the way it came off. This can cause a shudder, because the disc is slightly misaligned than before.
Had front discs skimmed off and it is now better than it's ever been. The best way is to skim the discs on the car. Otherwise you get the misalignment problem again if you remove them. After you've skimmed them on the car, mark the disc and wheel bolt, so that when you do remove the discs, you can put them back in the same position again.
What I can suggest you do is:
- Remove your brake pads and clean them with alcohol
- Put them back, and if the shudder is gone, replace your brake pads. Grease, oil and brake fluid goes into your pad and you can never get everything out.
- If the shudder is still there, I recommend skimming your discs.
- If your discs is too worn out, then you can't skim them cause there just isn't enough material left and you have to buy new discs.
The reason discs starts to shudder is warping of the disc. This happens when it is nice and hot and then cooled down rapidly. This happens when your brakes are hot and you drive through a large puddle of water, which splashes on the discs or when you wash your car after driving and you pour water on the discs.
Hope this helps.
Regards
Paul