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I would like to transport my MTB on an airliner's cargo hold. What are the requirements concerning hydraulic brakes, do they need to be flushed?

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  • You have two possible issues -- the pressure changes and the possibility that the bike will be turned on end or upside-down. Aug 13, 2019 at 1:43

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Tires on planes are a problem because they are pressurized above sea level atmospheric pressure. The pressure on a commercial airliner drops below that at sea level, so the pressure difference increases which can exceed the pressure the tire can handle.

Hydraulic brake fluid is not pressurized above sea level atmospheric pressure and the brake system is designed to withstand high internal pressure when the levers are squeezed anyway.

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  • What about the corrosiveness of the hydraulic fluid, is that not a concern for the carrier?
    – Vectorizer
    Aug 13, 2019 at 9:51
  • That would only be a problem for systems that use DOT 5.1 like SRAM. Shimano uses mineral oil. Brake fluid is not a great substance but it's no worse than the contents of many common batteries. Aug 13, 2019 at 10:00
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    We should clarify that some airlines think the tires are a problem, even though they are not. According to Jobst Brandt, Air France required his tires remain inflated to reduce the likelihood of passengers claiming damage to their rims (ref: yarchive.net/bike/air_transport.html)
    – Paul H
    Aug 14, 2019 at 0:38
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I flew with my MTB last year - no need to drain the hydraulics.

One thing you should do is get a couple of pad spacers to insert in the calipers whilst the wheels are out.

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I've heard of airlines requesting that you deflate your tires, but I've never heard of people draining the hydraulic fluid from their brakes.

Two friends of mine recently flew from the US Pacific Northwest to US Southwest for a week-long mountain bike trip. They flew with their bikes as checked luggage. By their accounts, they did not need to deflate their tubeless tires (thankfully), their fork or shock, and they did not have to drain the fluid from their hydraulic brakes.

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