You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
I’ve a length of Jagwire CEX outer which is brake cable. I need new shifter outer… will I die or have other problems if I use brake outer for shifter? Is there a genuine difference or is brake outer just tougher so there’s no problem?
By hose, I assume you mean outer.
It's a larger internal diameter which may affect indexing accuracy.
Brake outer is wider and wound like a coil so it resists compression. As long as the ferrules aren't too big to fit at either end, you'll probably be fine. I suppose there's more room for crud so it's maybe not a long term solution though.
IIRC, cex is spiral wound brake housing so it will compress slightly and throw the indexing out. Gear cable is made with longitudinal wire strand to avoid this.
Hmm ok, good reasons I guess.
What onzadog said!
Yeah as above... I actually tried this in an emergency when my gear cable snapped and mashed the outer with no spare. Works initially but needed to constantly adjust tension due to compression and good indexing was pretty much impossible. Might work on 9 speed setups where indexing easier but on 12 speed impossible
Buuuuuut Shimano do wound gear outer as opposed to longitudinal wire so may well work
Brake cable housing are wound so that they don't split under heavy load. Brake cable outer will work in an emergency as a gear cable, but may be difficult to index. Gear cable outers have longitudinal strands to avoid compression. They can burst under heavy load so should never be used as a brake cable outer.
Only the cheaper Shimano gear outer cables are spiral wound, the quality items have longitudinal strands to resist compression. A minuscule amount of compression can affect shifting on “modern” systems. Brake outers are usually 5mm external diameter and gear outers 4mm so compatibility with shifters, mechs and cable stops may also be an issue.
Hope this helps.
Buuuuuut Shimano do wound gear outer as opposed to longitudinal wire so may well work
I don't think I've ever seen spiral wound gear outer.
I'm kinda wondering how well compressionless brake outer would work.
IRC, cex is spiral wound brake housing so it will compress slightly and throw the indexing out. Gear cable is made with longitudinal wire strand to avoid this
This.
I don’t think I’ve ever seen spiral wound gear outer.
I didn't think it was a thing either, but I've definitely repaired friends' bikes (BSO's not "real" bikes) with spiral wound gear outers.
But then wehn I google OT-SIS40 the part that comes up is the cheaper of the complete Shimano shift cable kits (i.e. the one with unsealed ends and sp40 rather than sp41 (which IIRC was just whether they have grease pre-applied in the outer).

[edit crossed post]
what thols2 said.
Although using gear outer for braking does actually provide a firmer lever, and thus more power, so I have used that in the past. I'd not recommend it to others though...
I worked on a Giant Sportif bike a decade ago and all the cables at the front end were 5mm brake hose to the first stop. A funny shaped bike but it all seemed to work.