gjanssen

I'm putting together a 1991 Eddy Merckx Corsa Max and have encountered a snag -- the frame is supposed to have the rear brake cable routed through the top tube, but I have been unable to get a cable through the top tube. When I put a cable (just the cable) in through the hole/port near the head tube, it almost immediately runs into some type of obstruction and will go no further. When I do the same from the exit hole/port near the seat tube, I can push about 2 inches of cable in before it also meets an obstruction. Has anyone else encountered this? Any idea what's going on? I assume there is a small guide tube in there for the cable and the frame has been recently repainted (not by me), so maybe some paint found its way in there? Any suggestions as to how it might be fixed?

Duragrouch

Does sound puzzling. I don't have specific knowledge. However, a borescope may help, used to be an optical device that allowed viewing through narrow tube, expensive. But these days, there are electronic borescopes, much less expensive, with a tiny camera and light on the end of a tube or (usually) flexible gooseneck, that might allow you to look inside. Depends if the gooseneck is small enough to fit into your openings. Harbor Freight may be cheapest for this, if not cheap on amazon.

Also, you may try probing with a slightly bent spoke or piece of hanger wire, at different positions at the obstruction, see if you feel a path through.

Also, search online and on youtube, using your thread title here as search terms.

Andrew R Stewart 

My solution is to just run the casing outside the tube. Andy

rm -rf

Was there a brake cable installed when you got the bike, and did it work? Or is this just a frame?
From this 1991 bike image, it looks like there's brake housing stops at the frame sockets?
So just the wire runs internally? Or is it a continuous length of brake housing from lever to rear brake?




Carbon frame routing
My old Orbea had an internal routed rear brake cable. There's no internal tube (as I assumed it would have)! I pulled out the brake wire so I could trim the brake housing a little. Oh, it won't go back together!
There's a socket at each end of the top tube for the brake housing -- only the internal wire cable goes through the frame. The LBS fixed it quickly: the front frame socket was near the head tube. They routed a thin plastic tube in from the back socket and fed it out the front socket, with excess plastic tube on both ends. Now I could push the brake wire into that tube, and either trim the tube or pull it right out.
The correct method is to disconnect the brake wire from the rear brake, then feed new thin tubing over the wire until the tubing appears at the front of the frame. Now the wire can be pulled out, leaving the tubing in place. This is stock plastic tubing that comes in a bulk roll.

Here's my 2014 post with details and photos. Warnings for Internally routed brake cables

veganbikes

So cable is easy to bend housing is harder to bend. You generally want to use housing first and then cables because the cable will just bend and fray and hit stuff housing is going to have a tougher time with that

grumpus

Try a gear cable instead, if that goes in persist with the brake cable. When it comes up against the obstruction give it a gentle wiggle to see if you can get it in. Try putting a small bend near the end of the cable and twisting it gently as you push it in. I hope there wasn't a plastic liner in there that has been distorted in the paint/powdercoat oven.

mpetry912 

the time honored way to do this is get a piece of monofilament fishing line and feed it into one end of the internal tube, then put a vacuum cleaner hose up to the other end and the suction will dry it through. Then tie the fishing line to a cable and pull the cable thru from front to rear, with the front piece of housing on the cable. Then take the cable and use that to feed in rear piece of housing.

or some variation on that technique will get it there

/markp

grumpus

That's applicable if there's no obstruction, and you just need to guide the cable casing. This seems to be a bare cable run internally that won't thread in past the recess for the casing.

delbiker1 

Internal cabling can be a frustrating task. My Orbea Avant was quite difficult the first time, not too bad the second time, the third time, after learning to pull the slick lube tubing through the frame with the old cable. It was pretty simple. It allowed the cable to easily pass through. I now have a Shimano internal cabling tool that I do not use.

gjanssen

Yes, getting a look via a borescope is a great idea, but as you say, not sure if I can find one that will fit into the roughly 2cm opening where the top tube intersects with the seat tube, especially at the angle it needs to be to get in there via the seat tube -- tight fit! I'll look around to see what I can find -- thanks for the suggestion.

I've also probed each hole/port with a spoke with similar results. Even applying a bit of pressure was of no help. It's a frustrating mystery, and I'll keep searching, as suggested.

gjanssen

Right -- that is exactly the problem, thanks for clarifying for me. I am not asking about to thread a rear brake cable or cable with housing through the top tube of a frame; I know how to do that. What I am currently dealing with is as you say, a steel frame that quite likely has a tube (probably brass or stainless?) that runs internally from one hole to the other for the cable (and just the cable) to run from one to the other (see photo of Merckx posted above -- not my bike, but the internal cable threading is the same). Threading the cable in from the front hole results in the cable stopping 2 inches in, as though it has hit a wall. The same thing happens from the rear after about 4 inches. As you point out, it's obstruction that's the problem. I have no idea what it is, or how to fix it, and was wondering if anyone else has ever encountered a similar problem. I should also add, the frame appears free of rust and corrosion.

gjanssen

Right, that works great when there's not an obstruction of some sort. Frustratingly, no air will make it from one hole to another on my frame -- I don't have an air compressor at home, but I have tried to shoot air from one of those cans of compressed air made for cleaning keyboards into each hole, with similar results each time: the air just shot back out the hole I put it in. Whatever is obstructing things is airtight, or nearly so.

Duragrouch

That says a lot. But big difference between completely blocked, and a small hole for a cable. Put your lips on one hole, good seal, and blow into it; If it's totally obstructed, you'll know it, no air can go in. If you can blow air into it, then put your finger at the other end and see if you feel air. If you can, that trick with the vacuum and light monofilament line may work, to pull air through a small hole in the obstruction.

Why would they put an obstruction in the tube? Perhaps a long cylinder with a hole at the correct angle across it to guide the cable thru? Maybe to keep the inner cable from rattling in the inside of the top tube, making noise?

gjanssen

Ah, yes, trying to blow through it was actually one of the first things I did. No air went in, as you say. That why I tried the compressed air next, to see if a little increase in air pressure might jar something loose, but no luck (the seal was not perfect, but nearly so). So it really does seem as though it is totally obstructed.

You asked (rhetorically): "Why would they put an obstruction in the tube?" Who is the "they" here? The folks in the Merckx factory in 1991? I suppose they may have put something in there to prevent the rattling, but I have no idea what was factory spec on early 1990s Merckx frames. Maybe some expert on Merckx arcana can chime in and let us know (fingers crossed). As has been suggested in this thread, maybe there was a plastic sleeve in the guide tube (to prevent rattling) that has been melted for some reason and is now jamming things up. I really have no idea, which makes it tough to fix. This is a 33 year-old frame of whose provenance is unknown to me, save the person I bought it from (and who repainted it). It appears to be corrosion free, inside and out, has no visible damage from crashes, shipping, whatever else. All seemed well until I went mount the rear brake and . . . hmmmmm I appreciate your suggestions and will keep at it (and am definitely open to to more!).

Duragrouch

Repainted frame (I know, not you):

Antiques Roadshow: "Well, it would have been worth a lot more if you hadn't refinished it."

And yes, by "they", I meant at the Merckx factory.

grumpus

Ah, that's not good - seems like maybe some paint got in the hole, in which case you need to clear it. A 2 mm drill in a 2 inch hole when you can't see what you're doing is just asking for disaster, so your best bet might be a 5.5(?) mm drill to knock the bottom out of the insert, and run the cable casing through the frame. Before resorting to that you could try poking it with a red hot stainless spoke, which just might find the hole and soften the paint. Final options would be to have the whole insert replaced by a frame builder, or just run the cable externally.

Crankycrank

Cut an old piece of brake cable about 4-6" long on put it in an electric drill. Use the cable to bore through the obstruction. Don't get super aggressive and pull the cable out once or twice to see if there is any sign of what causing the obstruction on the cable end. Be patient if nescessary and just let the drill spin and do the work without too much force.