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hi volvo sages- bench bleeding a new master cylinder or bleeding it installed on the firewall required the step with the little hoses and fittings and pushed fresh fluid back in the resevoirs on top of the master cylinder long before the advent of abs systems. i remember doing this on master cylinder replacements in70s and 80s dodges and fords. you have to make sure that air bubbles come out of the hoses into the resevoirs. when you get a steady stream pumping back into the resevoirs , without air bubbles , then the cylinder dual piston is bled. i then saw mechanics do another step which is in some instruction sheets. quickly disconnect and remove the fittings and plastic hoses from the cylinder outlets and quickly hand tighten the brake lines to the cylinder. have a partner slowly depress the brake pedal.fluid will squirt out of the loose fittings with air like it is spitting. have a rag ready to deflect the fluid. tighten the fittings and wipe . the pedal may be on the floor. make sure the fittings are tightened. let the pedal up. make sure the resevoirs remain filled. this should remove any air from the lines out of the cylinder. the pedal should be normal now. the fluid will appear to spit out of the loose fittings as it displaces the air. i usually can do this in one operation. if the pedal is spongy or low, repeat this last step. remember basic laws of physics. heavier fluid will displace air if the air has a path to escape. regards oldduke
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