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Is there a way to temporarily plug and seal hydraulic disc brake hoses as well as hydraulic dropper post hoses, before installing them or removing them from a frame? The idea is to keep things tidy and prevent caustic DOT fluid from leaking into the frame (or onto the outside of the frame) while fishing internally routed hoses through the frame. I've just started to learn how to work on hydraulics, and I'm surprised I haven't found any rubber expanding pressure plugs (or similar items) like this.

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Normally you would route the hydraulic line before filling up the system and thus the line will be dry and clean. Once routed through the frame people rarely remove and reuse them, so your problem is not very common.

If for some reason you have a hydraulic line that you have previously used (on another bike perhaps?) or a hydraulic brake that came pre-assembled and pre-filled (apparently shimano do this sometimes) and you need to route the line that has hydraulic fluid in it, I would recommoned the following:

Empty the hydraulic line completely. There is no need to try and preserve the fluid in the line, it will need bleeding anyway. Once the line is empty, wipe the ends with isopropyl alcohol and tape them with electical tape. That will make sure you don't drip brake fluid inside the frame. After routing remove the tape, assemble the brakes and bleed as usual.

If I ever need to remove the hydraulic lines from the frame I tend to replace them with new ones.

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  • '... it will need bleeding anyway'? I disagree. The line is closed on one side and if you plug it on the other side (some manufacturers ,e.g. Magura supply plastic plugs with their brakes) and handle the line carefully, a full bleed does not have to be necessary. It depends on the frame of course, but I installed several brakes and never needed to do a full bleed. Commented Mar 11 at 14:57
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    I applaud your skill. I have tried that a few times, but always introduced an air bubble at the point where I had to unplug the line and connect it to the caliper/lever. It is possible to get away with partial bleed after that, but I tend to default to a full bleed given that hydraulic fluid is cheap and you only need a few cc of it per bled. Commented Mar 11 at 15:45
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Some internal cable routing kits will include a rubber sleeve to slip the end of the hose into and that sleeve is attached at the end to the line that gets dragged through your frame so that could work as a plug if the hose fits into the sleeve really tightly. Alternately some cable routing kits include a metal piece that screws into the end of the hose which would plug the hose. You would just need to cut that little bit of expanded hose off once you get the cable routed through your frame. I will admit I have never had to route cables internally, but I will be doing it for the first time next week and the routing kit I bought from Amazon includes both of the "plugs" I mentioned. The kit I purchased on Amazon was $17.00 and the brand was Coonium but I think it's also sold under the Risk brand since the magnet has Risk branding on it's side.

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