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How would I externally route the rear gear cabling on a Trek Allant 7.4?

It's had problems down shifting ever since I had the shifters replaced that can't seem to be repaired (Internal Cabling Problem?)

I'd like to convert it to an mid drive e-bike if I can get it to shift properly and afaik the motor I'm looking at can't be used along with cabling under the bottom bracket.

There's a cable entry point on the side of the down tube from the shifter, internal (no housing) cable lines under the bottom bracket, and an exit around the back of the chainstay.

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Assuming you have no cable stops on the outside of the frame, you'll need to use full housing all the way from shifter to derailleur. Simply run it alongside the top tube and down the right seat stay, and secure the housing to the frame with cable ties.

Its not the prettiest solution, but you're strapping on a motor, battery, controller, and wiring on anyway so looks are already going to suffer.

If cable ties aren't your thing, there used to be brackets for the top tube which would hold a rear brake cable on 80s style road bikes, or you could buy pairs of clamp-on cable stops of suitable size.

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  • Thanks! Is there a general guideline for how much slack I should have around the back between the dropouts and the derailleur and at the front from the handlebars to the top tube? Are there any tricks to good installation with zipties? I want the outer cable to be secure & not slip back or forth along its length, but also I don't want to cause resistance on the inner cable.
    – Scottmeup
    Mar 21, 2021 at 1:22
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    @Scottmeup not really - "slack enough but not too much" would be a guideline for the loop at the rear mech. At the bars, the outer should be long enough to not bind up when the wheel is at full lock on either side.
    – Criggie
    Mar 21, 2021 at 4:11
  • @Scottmeup for zip ties, you're not likely to crush the outer before the tie snaps. I guess you could find some fancy zip ties with nylon supports to hold the cable, or I'd just lay a thin strip of double-sided foam tape around the top tube, just wider than the cable tie. And then I'd lay the zip tie on top of that so it has some padding for the paint and resistance to sliding and abrasion of the paint.
    – Criggie
    Mar 21, 2021 at 4:13
  • Thank you. Is this the complete list of required parts for the cabling (excluding clamps): 1x Gear cable housing, 1x Inner gear cable, 1x Ferrule, 1x Cable end? I'm not sure about all of the part names. The shifter + derailleur are Shimano, so apart from the inner cable are the rest of the cabling parts a generic fit or do I need to look for specific diameter parts?
    – Scottmeup
    Mar 22, 2021 at 10:11
  • Two ferrules possibly - depends if the derailleur and shifter end need them, or not. Gear cable is fairly generic - your biggest option is choosing a colour, black is common but others exist.
    – Criggie
    Mar 22, 2021 at 10:21

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