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The rear calipers on my '85 245 needed changing, but otherwise the entire brake system was OK. I flushed and bled the system twice around at all four wheels using the low-tech pedal method, and got good hard pedal. But when I started the engine, expecting normal pedal drop from booster vacuum, the pedal went soft and traveled a good deal farther beneath my foot than it should. Subsequent pedalings had the same result. Whenever I release the pedal, the engine stumbles, as if there's a momentary vacuum leak. The single vacuum line between intake manifold and booster seems sound and tight on the check valve. And the one-way check valve seems to operate correctly when detached and blown through by mouth. I restarted the engine with the vacuum line detached from the check valve and my thumb over the hose opening. Releasing my thumb to open the hose stops the engine immediately. Releasing it partially causes the engine to stumble, suggesting a partial vacuum leak on pedal upstroke. I checked the FAQ for booster fault diagnosis and did the Swan test, but the pedal did not seem to rise against my foot on shutting the engine off, nor did I hear any obvious vacuum leak. Again, with the engine off, I have good hard pedal every time, so I assume the hydraulics are OK. I changed the master cylinder and flushed the whole system 18 mos. ago, and replaced the junction block last year. Any ideas out there? Thanks!!!
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