Your brake lever assembly incorporates a reservoir, the lever and the master cylinder driven by that lever. The reservoirs on many modern brakes have a rubber diaphragm that sits on top of the fluid to isolate air from it. The diaphragm allows expansion/contraction of the fluid volume without air contact when the brakes are operated and when they heat up, cool down and when the pads wear. With these designs, if your brakes are properly bled, there is no air in the system and you can turn the bike upside down without air bubbles 'rising' to the caliper. Some fluid may run back to the lever under gravity though (and this partially retract the pads) so you should always pump the levers a few times once the bike is right way up to readjust the pad position. If you do get air this way then your entire system needs to be bled and filled correctly. An intermediate solution is to store your bike vertically on one of those hook thingies. If you adjust it right, you can keep the levers above the calipers while still raising the front axle above the fork crown so that oil in the fork can run up to the wiper seal and foam rings. Sent from my SM-G935F using Tapatalk
