A neighbour was visiting and indicated that my front drivers tyre seemed a little low.

So I checked it and it was down to 20 psi - while I pumped it back up to 40psi the sun was shining through the wheel spokes onto the brake disk and I noticed what looked like a hair on the disk - on closer inspection I realised I had a cracked disk.

Click image to enlarge

I wouldn't worry to much about it, the sport is pretty hard on disks (heavy vehicle and automatic) but I've not heard of any issues with cracking. Have the disks been skimmed at any point ? if not put it down to bad luck and forget about it.

Disks and pads are cheap and easy to swap out

The disks have never been skimmed as it is something I do not believe in except if there is a gouge or not running true. Yes the cost of new disks is relatively cheap and I have ordered a new set - just was not expecting to do this now. 07MY RRS TDV6
Arctic Frost
Aspen Interior

Strange how its cracked in the same shape as the brake pads, even a nice neat curve at the bottom. I'm in the shed, I'll be back in the real world in a minute.

Russben - I noted your comment and filed it away but that was it - I should have put more thought into why that might be so.

I bought new disks at a good price and paid double what I should have for pads (the ebay delivered price was half the brake supplier).

Decided to replace the brakes and pads today. The pads were only 1/3 worn after 50,000km and of course had issues getting the caliper bracket off but it did come off in the end. I pulled the disk off and located the "crack" which is the same shape as the edge of the brake pad. On looking at the other side of the disk there was a mirror image "crack" and a "crack" where the other end of the pad would be - now getting suspicious.

All looked like cracks so I thought I would clean them up for a closer look under a magnifying glass - I used some cutting compound with no effect so got some wet and dry and the "crack" started to come off.

These are not cracks but "etch" marks on the disk. Just like as if you would do an acid etching on metal. Tough but if you persist they come off. All I can consider is that at some time the brakes were very hot and I stopped for a period with the brakes on and the outline of the pads was etched into the disk.

After sanding the marks this is how the disk looked - same spot as my original pic

Click image to enlarge

Click image to enlarge

Glad you got it sorted & updated the post.

I thought it looked strange having lvely radius cracks.

Mine leaves similar marks occasionally, normally if I've just washed the car, but they wear off eventually when using the brakes.

Russ. I'm in the shed, I'll be back in the real world in a minute.