Bike shop guys have been using this technique for as long as I can remember. Good luck. I use a length of small diameter tubing — a sort of sheath — to help guide the new inner cable no problems. For the first time I changed the cable myself yesterday.
I found the cable had an internal sheath that had jammed tight onto the cable where it turns under the bottom bracket — presumably from repeated stretching and rubbing.
Because of this the sheath was moving backwards and forwards with gear changes, and the top end where it exits the frame before going to the gear levers was jamming up against the end of the normal outer cable.
As a result the end was heavily wrinkled and further jammed the inner cable. Gear changes became very hard, probably leading to the inner cable breaking yesterday. Should the inner sheath remain on the inner cable through the carbon frame? If I leave the inner sheath on the cable inside the frame, does it need to be a particular type of sheath?
As well as the problems I can see advantages of leaving this sheath in position:- reducing the sound of cable slapping the inside of the down-tube, and possibly providing a reduced friction turn at the bottom-bracket. Your email address will not be published. Notify me of follow-up comments by email. Our cycling expert editors and writers choose every product we review. We may earn an affiliate commission if you buy from one of our product links, at no extra cost to you.
Leave the cable inner in place for now. Remove any plastic ports from the frame then remove the cable outers and cable ends from the open end of the cable. Place the thin plastic pipe on to the gear cable and feed it along until it reaches the other exit in the frame.
Fit the new inner cable to the shifter and cut a new length of outer cable if required. Thread the inner cable into the first piece of outer making sure the plastic end caps are fitted. Feed the new inner into the plastic pipe that is taped through the frame. Refit the last piece of cable outer and your gears are ready to be set up and indexed. Then once it's through you can size the hose by turning the bars as far as they go while holding the hose up to the lever and finding the length where the hose can't get accidentally kinked.
Cut it at the lever end and put on the spare barb and olive that come with the brake. Once you have the system reconnected, in many cases you'll find there's no need to even re-bleed the brake. Since you're cutting the hose, usually the fluid will be essentially flush with the cut. Only a marginal amount of air gets introduced, and Shimano brake reservoirs are able to absorb it.
That air floats up to the reservoir in the lever and won't be in the system during braking. If you do want to bleed it, usually only a "gravity bleed" is all that's needed, where you skip the step of shooting oil up from the caliper and just drain it down from the cup at the lever end into the collection bag or bottle at the caliper.
Basically this is taking Shimano's written procedure and eliminating the whole first half. The concept here is that you've only introduced air in the hose, which the gravity bleed will be well able to eliminate.
As for whether it's really better for brakes to come pre-bled, it's probably kind of a concession to giving people something they can just put on their bike and ride without needing a bleed kit or the ability to use it, etc. It's not necessarily the best way of doing things. Sign up to join this community.
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