sapporoguy

I'm working on my son's '80s-vintage carbon-fiber Kestrel 4000. See photos below.
Cabling is internally routed. The cable housing is embedded inside, so only the cable itself is replaceable.
The front-derailleur cable has broken internally. The break is about 10" from the top hole, and 1" from the bottom hole. The broken cable is stuck where it makes a bend in the bottom-bracket area. I have tried to push it through with a stiff cable; no dice. I've tried to grab a strand from the bottom with a tiny needle-nose; no dice.
I can see the cable housing through the bottom-bracket opening, but I'm loath to try to cut it open there.
Any ideas of how to extract a cable that's broken internally this way?
Is there a Kestrel 4000 forum somewhere?
Thanks!
The bike:

The cable holes bottom and top. The cable is broken inside, in between. The break ends just shy of the bottom hole.

The view up the BB hole into the downtube. The curved brownish thing is the cable housing embedded in the resin.

Lombard

Aren't internally routed cables fun - NOT!!

Are you sure the housings are inside the frame? Most internally routed cables have housings that end at the frame openings and it's just bare cable inside the frame.

sapporoguy

Yep, positive! The housing is inside, encased in resin.

Andrew R Stewart 

I might not use the term "housing" as that implies a metal reinforced tunnel. I suspect your frame uses a plastic tube (think aquarium filtering tubing). These bikes were designed early on in the "modern" era of internal routing and weren't too nice a method. It sounds like the cable has rusted tight in the tunnel and the tunnel is bonded into the carbon skin. When you grow tired or trying the near impossible consider going to exposed cables and housings. Some cable housing stops will be needed but could well be easier to make or find then surgery in a frame never intended to be able to be fixed. Andy

sapporoguy

Ah, that helps! Eyeballing the casing, I couldn’t tell whether there was metal in there. If it’s plastic, I wonder if I couldn’t carefully cut away a bit, perhaps with a dremel or Exacto knife and expose the cable enough to pull it out.

Andrew R Stewart 

It might be possible to bypass the embedded tunnels with fresh ones and still have them internal. Unsure how tight up to the cable entry/exit ports the plastic tunnels are. Unsure how much clearance between the ID of the shell area and the BB axle is.

People have used a vacuum cleaner to draw through a frame a length of thread and then attach an inner cable to that to pull the cable through. Sometimes sliding cable liner into and through the frame is possible. Good luck. Andy

Kontact 

Dowse the hole from both ends with PB Blaster or some other enzyme bolt loosener and let soak for a few days. Then try pushing it out with a brake cable.

You could also try getting some oxalic acid in there to eat the rust. Active ingredient in Barkeeper's Friend.

Finally, if it has a plastic lining, you could put a syringe of circuit board etching acid or some other acid that eats steel into the liner. Most acids don't effect plastic. Neutralize and push the remains out.

There is probably an electrolytic way of corroding away the cable using a car battery. Dunno. Science!

Lombard

At this point, I would bite the bullet and take it to a bike shop.

Kontact 

What's a bike shop going to do? I am a shop mechanic, and we don't keep a bunch of acids or carbon repair stuff on hand.

In case anyone doesn't know, the Kestrel 4000 is essentially the first frame of this kind. It is truly monocoque - they made it in one piece, in one mold, all at the same time. It doesn't have access ports under the BB. The inside is full of air bladders.

That cable is stuck because the bottom of the loop is a closed low point - like the brake cable on a mixte rear brake. The only practical solution is go make enough of the rust go away to get it moving again.


BTW, it might be worth an email to Kestrel. There might still be some corporate knowledge about this sort of failure.

smd4

As a former bike shop wrench, I like finding solutions to weird bike problems. But my gut's telling me that frame may be a goner. Unless you go the exposed-cable route.

sapporoguy

I should have done this first! I just sent them a message via their website and will report back.

sapporoguy

You’re probably right. If I can’t find a non-invasive solution, I’ll first get in through the BB hole and cut open a bit of that plastic housing and try to expose some of the stuck cable.

Darth Lefty 

Any chance of blowing it out with compressed air? Maybe with something like computer cleaner canned air instead of a compressor, it has the little tube and a smaller flow rate that won't endanger anything. Actually that tube itself might help push it out if you had a roll of it.

I happen to know one of the original Kestrel engineers through work. He's one of the three "real aerospace engineers" in the old magazine ad. But he was not a day-to-day guy assembling bikes and I am sure he would have no special idea how to fish out the cable that anyone here hasn't already suggested

sapporoguy

Yep, tried both air from my compressor and one of those computer-cleaner cans. I think part of the problem is that it’s embedded in a “U” shape where the housing curves from the down tube up to the exit in the seat tube. So pushing on one end makes it bind, rather than push out, I think.

sapporoguy

Here are two more pix to give a better idea of the place where the cable is stuck internally.
Bottom bracket with bike upside down, showing access hole and opening into the downtube:

Looking into downtube at the cable housing. The crumpled plastic is the bladder around which the fiber was wound, I think, and yes that's a Christmas-tree light in there. And spelled derailleur wrong.

Kontact 

I wasn't aware of the tunnel in the bottom of the BB. Come to think of it, I've never worked on a 4000, just the 200 and later series bikes. They were rare back in the day.

Given that the housing just acts as a liner rather than having stops, there is a stronger possibility of drilling out the old ones for replacement. But the problem area is how it gets around the BB shell. So you might want to stick to methods of getting the cable unstuck, first.

rccardr 

Would be tempted to spray copious amounts of PB Blaster into both ends and allow to soak overnight.
Then use a length of THIN hanger wire (the white coated stuff) to push the cable up from the BB and out the downtube port.
Don’t think you’ll be able to push it out through the curve in the bottom even though it may be closer.
I’d be pretty agressive about it, too.

icemilkcoffee 

Is there a way you can hook that housing and just yank it out?

sapporoguy

it’s embedded in the resin, so yanking would probably damage the frame.

ShannonM

If enquiries to Kestrel don't bear fruit, maybe an email to Craig Calfee might be worth a shot? Dude's probably seen every carbon bike ever made by now, and he's been doing repairs on carbon frames for many, many years. He might have seen this problem.

If there is a way to save this frame, this frame should be saved. Whatever you do, don't throw it away... even as wall art, it's worth preserving. It's one of the most significant bicycles of all time, and there aren't many of them left.

--Shannon

_ForceD_

I think I’d continue trying to push it out. But instead of using and old braided cable, maybe a steel wire of the appropriate thickness would work better.

Dan

dedhed

Piano wire

Lombard

Or a guitar string?