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Swapping hydraulic brake hoses from one lever to another?

I have (potentially foolishly) decided to try and replace the Shimano front disc brake caliper on my commuting bike as the original stopped working satisfactorily about 9 months in and LBS where I bought has been unsuccessful in fixing it. This and excuses given have led me to shop elsewhere!

Anyhow, I now have a BR-MT400 caliper to fit, which is one up from the one its replacing. I've bought a bleed kit and Shimano fluid and one weekend soon (or long lunch-break ;-) ) plan to fit it. While doing this I hope to switch round cables so that front is left, rear is right as this is my preferred set up. Also after fitting wider bars the cable to the front brake is on the limit of its reach but would be fine if set up continental style with the lever on the same side as the caliper.

My question is will it be possible to do this without having to replace all the fluid in the rear brake? I imagine some fluid loss is inevitable (e.g. from the lever) but if I remove the lever first and detach the hose with it held vertically I assume most of the fluid will stay in the brake hose and rear brake? The rear brake still works fine after 3 years with no servicing. Any tips on how to swap the brak hoses over and minimising fluid loss would be welcome.

I am expecting to have to replace all of the fluid in the front brake and have two bottles of fluid, enough for each brake apparently.


  • reaperactualreaperactual Posts: 892
    edited September 2020
    No matter how careful you are consider this as a messy job (especially the first time) and you will lose a small amount of fluid. The small amount of fluid lost could be enough to effect final braking performance.

    What you are intending to do is straightforward enough. The biggest mistake you would be likely to make is contaminating rotors and/or pads.

    Best advise is to remove the whole braking system, remove pads and proceed with all tasks away from the bike.

    Shimano recommend replacing all hose fittings (olives and inserts) whenever disconnecting hoses. You can do it without this step but keep an eye out for any leaks at connections over the next few weeks.

    I definitely recommend a full bleed with bleed block for both brakes afterwards, this will give the best results and be the safest option. You have a bleed kit, make use of it.

    Clean all components and your hands thoroughly to get rid of any fluid before re-fitting pads and fitting everything back to the bike.

    Beware your calipers may not have a bleed nipple pre-fitted so you will need one of these or make sure your bleed kit has the relevant adaptor to do a full (caliper up) bleed, especially on the rear seeing as the fluid is 3 years old.

  • mully79mully79 Posts: 283
    Epic bleed solutions did a good write up on how to shorten hoses on pre-bled shimano brakes. Obviously read it until clear and cut out the shortening hose bits.
    if it all goes pear shape resort to the bleed kit " plan b."
  • Thanks for the advice, still sounds pretty daunting but have to give it a go as bought parts and tools now
  • Daunting the first time but easily doable with a little care and taking your time.

    The second time with more confidence it's child's play! 😎👍
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