What are good ways to remove initial cable slack when replacing rear derailleur shift cable housing?

Question

I needed to change the cable and housing of a rear derailleur lately, and what I usually do to help with the initial cable slack is:

1. Install the housing end caps on the newly cut housing and strike them a few times on the bench top to seat them.
2. Route the cable and housing on the bike, put the chain to smallest cog, shift to highest gear and pinch the cable in the rear derailleur while pulling the cable by hand to remove some slack.
3. Shift gears a couple times to seat the end caps further.
4. Detach the cable, remove slack again by hand and pinch again.
5. Proceed with gears adjustment.

The thing is this time, after adjusting the gears and finishing the other maintenance tasks on the bike, when I tried shifting gears again, there was still slack. I needed to detach the cable and remove slack again twice.

For this job, regular 4mm Jagwire shift cable with plastic end caps were used. There were three housing sections (so six end caps).

I would like to know if there are good ways to help remove the initial cable slack and make sure it is all gone before calling the maintenance done. I know we can sometimes pull on the exposed cable to help seat the end caps but I already broke a grip shift doing so and I am a bit hesitant now with this technique.

Answer 1

On interrupted housings, the best practice for pre-stressing it is do the thing you're hesitant to do: pull hard on the exposed cable. The shifter always has to be in the zero-pull state when you do this, but there should be no fear of damaging anything if so. For a front derailleur with the chain on you'll have to turn the cranks manually as you do so. For a rear derailleur with the chain on you'll also need to move the cranks, but with the chain off you'll instead need to manually push the derailleur out of the way so it doesn't ram into the cassette.

It increases the chance of one-shotting the process to put a little grease inside each ferrule as a matter of habit. I do a very small amount taken by lightly dragging each ferrule against the top of a grease pot lid. This isn't critical but it does make them seat faster.

This question is different for other housing configurations. If the housing is continuous, or if it's interrupted but with the bare cable sections internal to a frame, then you don't have the ability to pull on an exposed section cable. Here the best practice becomes to use a fourth hand tool against an appropriate surface (frame, ferrule, or part of the derailleur depending on the situation) before the cable anchor is secured. This is particularly good for dropper installations when the cable head is at the control, because if you don't do it before anchoring the cable, there's little you can do afterward to keep from needing to use a lot of barrel adjuster immediately - seldom will you want to go back in to re-anchor the cable.

When using the fourth hand method to pre-stress derailleur cables, you must have a plan to do so without putting a crimp in the system where the fourth hand is squeezing the cable. You can use a surrogate piece of housing, for example.

The fourth hand method isn't perfect, but is often the only choice.