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I had an incident recently that resulted in a damaged hydraulic hose. It was munched by the chain.

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Curiously, the brake still holds pressure and functions, though I have limited confidence in it. I'd like to trim the damage off and fit the caliper to the cut-end.

The hose is labelled "Shimano SM-BH59-JK" and while the caliper is bottom-end I would prefer to not replace the whole thing.

enter image description here

These are the spares that came with the pre-bled caliper set, so I presume its what's needed. I guess the round barrel is the Olive.

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My plan is:

  1. unbolt the ~8mm nut where the hose enters the caliper and draw it back. I expect to find the same two brass parts in the end, but that they will be secured and not reusable. The caliper will be full of Mineral Oil, hold so it doesn't leak out.

  2. Cut the hydraulic line just above(left) of the damage. Again, its got fluid in there. I will use some crossover cable-brake outer cutters.

  3. Smooth off the cut end and open up any liner. There's obviously a braided mesh in there.

  4. Move the existing nut to the good hose, above the cut.

  5. Fit the new brass olive over the hose.

  6. Insert the new brass pin in the end, and make it look like the cut-off piece in offset and layout.

  7. Insert the prepared end of hose into caliper and tighten down the original black nut.

  8. Refit caliper to mounts, align caliper, test.

Do I have everything I need? Are there any oversights or errors in this method?

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2 Answers 2

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Sounds good to me! Just a few more pointers:

  • You’re going to have to bleed the system for sure, so don’t be too worried about losing fluid.

  • Hopefully you have enough excess hose to make such a repair. That’s quite a bit cut off.

  • The insert (brass pin) is delicate. Careful when pushing it in, as it may require a bit of force — it likely won't just slip in. A bit of oil helps lubricate it as it goes in.

  • A bit of oil-soluble grease or even the brake oil applied both under the olive and on the olive helps it deform more smoothly as it gets crimped onto the hose. Use grease very sparingly as to avoid contaminating the oil too much.

  • Make note of how deep the 8mm compression nut is threaded in on the current setup, and keep that in mind when tightening. It’s a fine thread in soft cast aluminum, and you are tightening it against a soft stop (can’t feel a definitive end). It’s relatively easier to strip the threads by accident.

  • Of course, remove the caliper from the bike, and remove the pads. You might as well clean the caliper and pistons while you’re there too.

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    I'd add that that barbed brass end is difficult to get in. Have something to ream at least the first couple mm's of hose to ease the insertion. Not so harsh as to split the hose as you have little room for more trimming. Have also a hammer to encourage that pin to go fully in. When the nuts begins to thread on smoothly push the hose against the stop in the caliper (static force on the hose as you torque the nut down). I've had good luck avoiding a full bleed when trimming hose from the lever end.
    – Jeff
    Commented Jul 4, 2021 at 3:12
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Well I'm all done - some things that would be better done differently.

  • Use a quality 8mm spanner. Mine was a bit sloppy, and I've rounded off the nut that enters the caliper. It took a lot more applied force to do up, because the olive needs to be deformed.

  • Expect to do a brake bleed. I took care to work up high, above the level of the lever, and despite that the finished system is soft and bottoms out the lever. I saw no fluid leak out, no drops anywhere, just a small wet spot on the caliper.

  • Jeff's idea of reaming the end of the tube is good and you should do that. I used a small hammer to tap in the pin - it was definitely not a press fit. To hold the hose I grasped it in pliers, which marred the outer surface and caused the olive problems slipping over the outside.

  • Later - the brake turned out to be soft like jelly, so it needed a bleed. I've done that on cars before, but not on hydraulic bike brakes, and it was similar-but-different. The caliper connection for the syringe was poor, should have bought the fancy clips, and I was surprised how fluid Mineral Oil is. It runs almost like water, and will wick into things. I contaminated the rotor, but avoided the brake pads. Had to acetone clean the rotor and all was well.

Useful references:

Original olive in compressed state, as removed from caliper.

enter image description here

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    It was @Jeff who recommended reaming the end. I'll update the "press-fit" wording; I meant to just say "it may require some force to insert, as it is not purely a slip fit".
    – MaplePanda
    Commented Jul 4, 2021 at 5:03
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    There is a tool to hold the brake hose when putting the pin in: Shimano TL-BH61. Clamp it somewhere, it won't damage the brake hose. There's also a tool for tightening the flare nut: Park Tool MWF-1.
    – juhist
    Commented Jul 4, 2021 at 7:59

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