I have a new Shimano shift lever that has the inner cable already attached. My question is; can I just remove the old lever, withdraw the inner cable and feed the new cable down the housing to save dismantling the new lever to swap the cables over? Or am I better off using the new housing and replacing the whole lot at once, or do I take the new shifter apart and attach the existing cable? The cable housing is internally routed, although it goes behind the battery so looks easy enough to access if it get's stuck.
My problem with taking the shifter apart is that the manual mentions a self tapping screw that goes into the plastic and I don't want to risk over tightening or it not screwing up again... (or is that a non issue??)
Cable has to be detached from the rear mech and withdrawn through the outer.using the existing outer is fine assuming it's not damaged, bent, dirty or frayed at the ends. You could reuse the inner but it will need retreading. Easier just to use the new inner that's already installed as the soldered end makes passing it through the outer easier.
In future, cable replacement will require that plastic screw to be removed but it's a decades old tried and tested non issue.
I'd use the new cable. It should just slide into the existing outer. If you used the old cable you'd still have to rethread it and that will be trickier as the end will likely be a bit chewed.
When you do need to change a cable it isn't a big deal. Unscrew the plug, put the shifter in top gear, push the old one out, thread the new one in.
Thank you 🙂