leting the system drain completly is a ballache. you will need a pressure bleed kit to refill it properly.

i found this out after 3 unsuccessful (2-man) bleeding attempts. i left all 4 calipers off for a week to drain

wether letting its drain compared to just putting in new liquid and pushing out the old is better is questionable.

i imagine a drained system would have a thin layer of old fluid around all the pipes and parts etc. so when you add new fluid there is no "pushing effect" on this old fluid. and some would be left in.

on the flipside doing it the other way would possibly negate the said previous problem. however you may also have sections of the brake system that have larger pockets of old fluid sat in them that may not be emptied as well as by a complete drain.

or im talking crap, which im sure ill be called up on below

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