In general the rear brakes are useless on the SS. Try bleeding the line a couple of times and see if it gets any better. I NEVER use my rear brake. (Only sitting at a stop on incline/decline) Maybe you can use the driveway and see if it keeps the bike from moving. That will at least tell you if it is working at all. I locked my rear one time in a situation where I wasn't paying attention on an unfamiliar road, going too fast to find out the turn coming up was waaaay sharper than I thought. I think grabbing a handful of front brake helped bring the back up enough to lock it in that situation.
