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This is a fairly common problem on the older 240 series. First, remove pressure from the bleeder, remove the bleed nipple, and use paper clip or fine wire to clean any rust/gunk/debris out of the bleeder hole. Reinstall the nipple, put a heavy duty wire tie around the master cylinder and reservoir, and set up your bleeder for about 25 psi. Then open the bleeder and have someone step on the brake - HARD - but not all the way to the floor (put a piece of 2x4 under the pedal so that it doesn't get bottomed). Often in addition to the caliper getting gunked up, the proportioning valve gets clogged as well. Once you get it flowing, the pressure bleeder will work fine without the pedal. Be sure to flush a lot of fluid through - good idea to drive for a week or two and flush again - you will probably get more crud out when you do.
CAUTION - if you use enough pedal pressure to force the blockage through, there is a good chance that the blocking valve will move. If your system has not been flushed every two years since new (I don't think that I have ever seen one that has had this kind of care), there is a good chance that the blocking valve seals will be damaged by corrosion and that it will start leaking - solution is to replace the blocking valve with new. To check for leakage, remove the brake warning switch (plastic piece svrewed into the top of the blocking valve assy) and look for any evidence of brake fluid - it should be clean and dry inside.
****Any leakage here can bleed down both sides of the dual system and result in total brake faulure with no warning light!!!****
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