I want to swap the handlebars for a different pair. I have hydraulic brakes. When i remove the master cylinders from the old handlebars is it necessary to keep them upright, or keep them above the brake callipers? Is there anything else I should be wary of during this procedure?

  • 1
    On road levers, the master cylinders are inside the shifters for sure. I was under the impression that this is true with MTB levers. I assume you mean removing the brake levers, rather than just the master cylinder, correct?
    – Weiwen Ng
    Commented Sep 20, 2021 at 18:25
  • @WeiwenNg yes you're right - almost all bike brakes have one master or input cylinder which is built into the brake lever, along with generally two slave cylinders inside the caliper.
    – Criggie
    Commented Sep 20, 2021 at 23:48

1 Answer 1


There should be no problem turning your master cylinders upside down for a short time.

I've found that the worst thing that happens is that it might take a bit of pumping action after you right the master cylinders to get them working as expected again but generally even that is not needed.

If there is air in the system it can require bleeding but you'd already be having issues with the brakes if that were the case.

  • This is true though some designs like shimano's mtb, trap air in the reservoir which can leak into the system when upsidedown. It takes a while to come out again (pumping) but should be bled out in an ideal world.
    – Noise
    Commented Sep 20, 2021 at 19:07

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