Hydraulic brakes+air in the system?

[Mojoman]

I am busy looking at hydraulic brakes on my possible future bike, but I have read somewhere that you need to be careful when laying the bike down on its side, and turning upside down as the brakes can then get air in them,...any truth to this?

[Johan Bornman]

No

[Mojoman]

Am just checking its safe to lay the bike down in the back of my car or for when I fix a puncture. Thanks.

[kosmonooit]

Having just refitted some Shimano brakes, the documentation does warn you about this and says it can happen. However I havent ever had the problem but never say never.

I think the way it can happen is that if there is some air in your reservoir, and your bike is inverted, and the handle pumped inadvertantly, the air can enter into the system but thats just a theoretical speculation of my part as to the warning in the Shimano documentation.

[Mojoman]

Thats where I came across this, in an online Shimano manual. I thought the brakes were like a car's,..i.e a closed system, the only way to introduce air would be to have leaks in the tubing/piping/unions or in the reservoirs or at the caliper end?

[kosmonooit]

Yes they are a closed system but the reservoir might have some air still in it even after bleeding, even though there might be techniques to remove that before closing the lid. I just filled it up to the point of overflow, put the diaphragm it and caught the overflow with some tissue paper and hoped for the best. I cart my bike(s) around on their side.?