Had my first crack at bleeding brakes yesterday after many years riding. I don't have a bike stand, but thought it would be a good idea to hang the bike off the washing line and stand on a chair so the bubbles would go up to the levers. Slowly tightened the bleed port whilst keeping pressure on the syringe, only to have the bleed hose come off the syringe and shoot mineral oil all over the dining chair I was standing on. At least it wasn't Dot fluid, thanks Shimano.
Also, don't tell my wife.
I hate to tell you that the best way to bleed Shimano had little to do with orientation of the bike.
Push out the old fluid into the cup, empty the cup, top up with some fresh fluid about 1/4 of the way, pull oil back into syringe and then push back into cup a few times to get the big bubbles.
Now here is the important bit. Close the bleed valve on the caliper and do short flicks of the lever lots, you should see lots of little bubbles rising into the cup. These are small bubble trapped near the master piston and the reservoir. When the bubbles stop, prime the brakes by pulling on the lever until the brake is pressurised.
Finally open the caliper valve and force oil into and out of the cup one last time and check for bubbles, then close the caliper valve, remove cup and replace bleed screw.
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