the 280mm and 300mm disks use the same calipers (sort of)and pads, but the bracket mounting the calipers is longer for the bigger disks. The bracket IS NOT available separately from the caliper either from volvo or the oem manufacturer - i have tried both routes.

the only option to use these disks is to buy a set of the calipers.

if you order them from volvo, they will charge a refundable deposit against return of the old ones, but you just keep quiet and pay the deposit, then dont return the old calipers - if you say what you are planning to do they may not take your order.

part numbers 8602344 and 8602345 (sided parts)

the deposit in the UK is about £60 each, and the price for the calipers is about £120 each - so not a cheap option.

the aftermarket big disks use different disks (usually directional), multi-pot calipers and custom mounting brackets - the classic example is the AP Racing 4 pot kit with 325mm disks at about £1400 - these brakes are amazing but expensive.

volvo made/make their own big disk kit - 320mm directional disks, single pot calipers and special pads - this kit costs £1000, but braking is a world apart from the standard 850 / 70 brakes. you need 17" alloys for anything bigger than the 302mm disks though.

i fitted the volvo 320mm kit and am amazed by the brakes every time i drive this car. down side is that disks are £300 per side replacement, calipers £250 per side, but pads are only £65. i wish i could find the oem manufacturer for this kit because i would like to see if i could get the disks cheaper.

hope this helps some...