I have an 06 YZ250 and race motocross. Had a real big tumble that ended up with me in an ambulance, but apparently no serious injuries. I was riding morning practice and went a** over teakettle on the 100 ft table. Once I recovered enough to do some playriding I jumped on the bike and discovered I had no rear brakes. Got home, tried to bleed the brakes and got nothing. I pumped and pumped and got a little fluid to piddle out, but never got enough pressure to actually move the pads. I took it in to the shop and vacuum bled the brakes. Seemed to fix the problem, but after about 15 min of riding the brakes went away again. Took it home, tried bleeding the brakes again and nothing. I just put a new stainless steel brake line on (old one was stock) and the brakes bled right up, no problem. Good feel at the pedal, but I haven't ridden it yet. Gonna go out tomorrow and play in the snow a bit to see how it works. My question is, why would changing the brake line fix this problem? My thinking was that fluid was bypassing the piston in the master cylinder but it seems like just swapping out the brake line fixed it. Anyone seen something similar before or have any thoughts?