When I originally bought the car, it had a nasty judder under braking. I incorrectly assumed that this was down to unbalanced wheels. After getting them rebalanced a couple of times things improved slightly at motorway speeds, but brake judder never fully went away and was only getting worse.
Not knowing my options, I bought and installed a new set of brake disks/pads. The issue went away - result! Unfortunately it slowly started to reappear and got worse over time. Thinking that I warped my disks again, after a few road trips and spirited runs, I decided to get he disks skimmed by a local workshop, which came highly recommended. Once done, this fixed the brake judder problem and I was happy, for a while.
Very soon after the disk skim, I had the new BBK installed, but after just two or three thousand miles I started to notice that familiar judder coming back. By this point I was getting rather annoyed at the amount of money this was beginning to cost me as well as the frustration of having a nice car that I did not enjoy driving. After doing a bunch of reading and asking friends for advice, I found Marcus, who runs a place called Disk Skimmers near Cambridge. Top guy and knows his brakes
The moment he took one of the front wheels off, he showed me my problem! It turns out that my OEM wheels were refurbished at some point, using powder-coating. It was very good work, but the process also resulted in a very fine layer of coating left on the inside of the wheel which mounts to the disk. This fine layer of powder-coating was enough to cause an imperfect contact between the wheel and the brake disk, which caused the disk to start to deform slightly. We're talking microns here, but this is enough to cause the nasty judder that I came to expect from my car.
The solution was quite simple - light skim of the disks to fix the damage that was caused by the bad contact with the wheel. (This is normally as far as most disk skimming places go and fix the symptom of the problem, but not the cause.) The second part was to sand the mounting surface of the wheel down to get rid of the powder-coating, then a very light filing of the same to make sure that the mounting surface was completely smooth and level and ensure a perfect contact with the disk. The reason that the filing was required is because the alloy of the wheel will actually try to 'mould' around the powder-coating with every heat cycle. Marcus knows his stuff - http://www.discskimmers.com/