i have some experience with this. not the actual implementation of the internal routing with full length housing, but I have experienced issues with this frame's internal routing, so i have done a bit of research on this topic over the years, but not yet implemented. my FM-057 (pretty sure it is the same frame still) has just turned 6. it lasted a couple of years with internal cable routing for the rear shifting, but it deteriorated over time, such that i ended up externally routing it. i did consider the idea you are thinking (trying to get the housing through the frame), but, at the time, i couldn't see how it could be done, and i did read at least one or two stories of people who did it (buried somewhere in the monster thread on mtbr), and i got scared off - they didnt really detail how they did it, what their issues were, but they advised against it. so i have been running external routing for at least 3 or 4 years now.
only a couple of months ago, i have become interested in this topic again, as a pretty bad rattle has suddenly developed, and i have traced it to the empty internal routing for the rear shifting, seems to be around the area near where it attaches internally around the head tube area (i.e. the front cable stop). i'd love to remove that internal routing tube to get rid of the rattle. problem with this frame is the access - with the BSA BB shell, there is no access around the BB area, the only access is in through the head tube, and while i have considered drilling out the cable stops at each end (near the head tube, and the one on the chainstay), i cannot get a good enough view (in through the headtube with the fork off) to know for sure if the internal routing tube is attached/glue/fastened somehow around the BB area, so it would be a risk to drill out the cable stops, as, if the internal routing tube IS attached around the BB area, and i drilled out the cable stops, i would end up not being able to pull out the internal routing tube, so it would end up loose in the downtube, probably rattling even more. so i gave up on the idea again.
but the rattling over the last month is starting to get to me.
your thread has prompted me to have another look at this.
there doesnt seem to be any thorough explanation anywhere online on how to perform this task on this frame.
but, this time around, i found this old thread (surprised i didn't see it before):
https://forums.mtbr.com/29er-bikes/chinese-fm056-frame-internal-cable-routing-flexes-stretches-792079.htmlthe fm-056 is the same frame as mine (and probably yours), except it has different rear dropout (i think it might be 135mm only).
it sounds the OP on that thread got some good vision of the going ons inside the frame, using an endoscope, but sadly his vids and pics dont seem to be on youtube anymore. however, i did get a few key takeouts:
- the internal routing tube is NOT attached to the frame in the BB area, so the only attachment points are at the two cable stops (i.e. at the entry/exit points, one at the front, and one on the chainstay),
- so drilling out the cable stops at each end will be enough to detach the internal routing tube from the frame.
After drilling out each end, the internal routing tube would have to be pulled out of the frame, and the only route to do this is out through the headtube. I am not sure what tool to use to get in through the headtube and grab hold of the internal routing tube, to pull it out. gonna have to think this through before drilling out. if i cant find some kind of super long nosed (and curved) pliers, i have an idea that might work: partially thread a gear cable through the tube (from the rear), do some fairly precise drilling/cutting (either with a very small drill, or some kind of dremel attachment) around the inside sides of the rear cable stop (to detach the internal tube from the frame), then drill out the front cable stop (detaching it internally), then push the gear cable the rest of the way, the objective being to get the end of gear cable to poke out through the top of the head tube. then pulling the gear cable out through the headtube would take all of the internal routing tube out with it (the head of the cable will pull on the detached-from-frame rear cable stop).
the next step would be to route the housing through the frame. this would obviously go through from the rear (as i have doubts that just pushing the cable from the front would just magically go out through the rear exit), and there would be a risk that simply pushing it through might not work, as it has to get around the bend in the BB area, and i cannot see if there are any angles in the carbon on the interior of the frame around the BB area, that a cable being pushed through would get stopped by. internal snags when pushing through housing are often gotten around by putting bends/kinks into the end of the housing before pushing it through, and failing that, pushing through a more easily bent cable (inner) might work, using gravity to help (i.e. have the frame upside down when trying to push the cable through the bend in BB area), then using the inner as a guide to thread an outer over it. there would still be a risk it wouldn't work. having said all this, perhaps this routing-of-housing step could be better done if it was combined with the previous step : attach the housing to the end of inner cable that is used to pull the internal routing tube out of the frame - not sure how to get it firmly attached though (i have tried this before using insulation tape, and it almost always does not hold).
the last step would be to get the housing out through the front exit. this would be quite hard to get it to line up perfectly and go out through that exit (as that hole is the same size as the housing), but i got some idea from one of those threads : have the end of the cable housing behind the front exit (down towards the bottle cage slightly), then push a cable inner through the housing from the rear and then get the inner to go out the end of the housing (inside the frame), the out through the exit (would be much easier to inner cable to do this than housing, as it bends easier so can be directed easier (either with gravity and/or by sticking a wire down through the headtube to try directing/manipulating it), and is thinner so will go out the exit easier), then thread another piece of (short) housing onto the cable inner that is poking out through front exit, then push that housing in through the front exit (so some of the housing is in the frame, some is still outside) then push the "main" piece of housing from the rear until it butts up against the short bit of housing (so the short bit of housing becomes a guide for the main housing), then push it some more (again, from the rear of the bike), and it will come out through the front entry/exit hole.
before the last step (i.e. before the housing is pushed out through the front entry/exit hole), it would probably be a good idea to feed some capgo noise protection onto the length of housing that will reside in the downtube. this optional step would be pretty easy (push the housing out through the headtube, then thread the noise protection tubing over it), and would virtually eliminate any risk of cable rattle.
as the rattle in my frame is bad as it is, i now feel that i have nothing to lose, so i am gonna try doing the above. as i have had some pretty tricky internal cable routing jobs over the years now, i am quite aware how difficult, time consuming and, above all, frustrating, some of the above steps are. am i also aware that there is a risk that i might not successfully complete the above described steps. eg1. i fail to pull the internal routing tubing out of the frame (but i doubt the rattle caused by loose internal routing tube would be much worse than i have now). eg2. i fail to get the housing past the BB area (in which case, i'll just continue to externally route).
anyway, hopefully you get a few ideas of how you might go about doing this task. i'll let you know how i go, but it'll probably be a month or so until i attempt it.
the reason this process is so difficult is because there is no access around the BB area. Just in case they have changed things over the years, and your frame is different to mine, the first thing you should do is remove the BB and see if there is any access (holes) inside the BB shell. If so, this process might be much easier (the less risky) on your frame than it is on mine.