Pressure bleeding brakes, nothing comes out of the rear bleeders

[Epic2112]

My M3 has been in storage for about 6 years. During that time it sat unattended, unfortunately, so there are a number of items that need freshening up. Everything seems to work fine, but the brakes definitely don't feel as solid as I remember them to be. Today's agenda is checking them over. The pads look fine, so I've started bleeding them with a pressure bleeder. When I crack the bleeders on the rear calipers nothing comes out. This is the case for both sides. The bleeder is at about 15psi, and the front calipers bled normally.

I'm thinking something is clearly wrong with the rears, and maybe a line got clogged somewhere (and maybe that's what was making the brakes feel the way they did), but I've never heard of a brake line getting clogged. Any thoughts or suggestions? I also wanted to rule out the ABS system, if this could somehow be related to that.

Thanks for the help!

[Dave @nz]

Hi
It has been years since I last used a pressure bleeder ,are you pumping the pedal while bleeding if not that may be worth a try just incase there is some sort of valve in the rear system.
Short of that remove the nipple and check it for rust blockage may just require a drill running through it.
Good on you for getting the M3 back into action.

[mtony]

I would try spreading the inner brake pad away from the disc with the bleeder open and see what happens. If you get some fluid out that way, I would then try an old fashioned pump the brake pedal bleed with the engine running to see if you get fluid through that way.

[Epic2112]

It's just me, so I wasn't pumping the brakes while bleeding. I did close the valve and pump the pedal a few times. After that I was able to get one of the rears to bleed, but still nothing from the other. It's not the bleeder screw, I unscrewed it almost completely just to rule that out. If the screw was the problem fluid would have come out of the hole when I unscrewed it. I'll have to try again when I have a helper, and also try pushing on the pad. Hopefully one of those will do the trick. In the mean time the car stops OK...