Rear Brakes Going Away

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?

The brake line was pinched somewhere? Thats the only thing I can think of. Glad your ok though.

definately a leak in the line somewhere

I like the other guys ideas for sure. Your rear master cylinder could have taken a shot and needs to be rebuilt. Very easy job .

Thanks for the replies. I had a look at the brake line that came off and there was no visible damage. No bulges, pinches, or bends. Also no visible leaks or loss of fluid volume. I'm gonna head out for a ride and see how it does.

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