[sperry]

The rear sti brakes are meant to fit on a car with an r180 rear diff instead of the smaller r160 that the wrx has. This means the backing plates and rotors are all designed around a larger rear bearing. The ebrake on the sti is larger in order for it to clear the larger rear hub.

There are ways to shim the wrx ebrake to mate to the large diameter rotor, but I believe they assume you're also converting to the 5x114.3 hubs. I don't know that it's possible to get 5x100 rotors that mate to sti brembos without drilling them yourself.

To be frank the right way to convert to the sti rears is to replace the rear diff and everything down the line, including the spindles and hubs and going to 5x114.3. Which is insane when you consider the brembo rears are really no better than the fhi 2-pot rears from the '06/'07 wrx. Furthermore, I would suggest StopTech brakes up front over the sti brembos as well. The brembos are good brakes, but there's a reason why sti owners drop them for StopTechs or for the race brembos. Unless you're getting a killer deal on the sti brembos and you're already switching to sti knuckles/hubs on all 4 corners, I think you can get better brakes for cheaper by smartly upgrading just the front brakes. People that do the sti brembos up front only end up thinking they need the rears because their bias gets all screwed up not because the 2-pot wrx rears suck. The right front bbk designed to match the 2-pot rears works very well. Ask the folks that are running that setup (Im one of them... on both the race car and he svx).