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Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Mon Aug 06, 2018 11:23 pm
by iamoutside
Please see the picture attached.

I was installing my front gear cable and forgot to insert the small black plastic tubing that the cable goes through when it exists the pre-drilled internal cable hole above the bottom bracket in the frame on its way to connect to the front derailleur. When I did that I tested the front derailleur shifting on the bike stand and the cable started sawing right away into the carbon fibre frame because i forgot about the little tube to protect the cable from rubing into the frame.

I installed the plastic tubing after this happened and now the tube is getting cut as it hugs against the frame tightly when connected to the front derailleur. So I tried to use much thicker plastic tubing and its still getting wedged inbetween the slit that was caused by the cable sawing into the frame and I am worried the plastic tube will get cut open and the cable will continue to saw into the downtube.

I am wondering if I can sand the sharp edges down so the hole can be smooth again? The frame is carbon fibre. Would it be safe to do so?

Any thoughts?

Thanks

Re: Gear cable sawed through internal cable hole

Posted: Tue Aug 07, 2018 12:03 am
by DamonRinard
Good idea. I'd do it.

Re: Gear cable sawed through internal cable hole

Posted: Tue Aug 07, 2018 12:03 am
by Weenie

Re: Gear cable sawed through internal cable hole

Posted: Tue Aug 07, 2018 12:47 am
by iamoutside
DamonRinard wrote:
Tue Aug 07, 2018 12:03 am
Good idea. I'd do it.
Is it safe to do so on a carbon fibre frame? Any special sand paper or tool?

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 12:55 am
by alcatraz
I would use a dremel.

How about other front derailleurs? Do they have this problem?

Are you sure the cable routing under the bb is correct. Sometimes the cable guide there can be turned around by mistake.

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 1:02 am
by iamoutside
alcatraz wrote:
Tue Aug 07, 2018 12:55 am
I would use a dremel.

How about other front derailleurs? Do they have this problem?

Are you sure the cable routing under the bb is correct. Sometimes the cable guide there can be turned around by mistake.
Hi,

This is my only bike, not sure what you mean by other front derailleurs. I am on a Cervelo S2. The cable routing for the gears runs inside the downtube and out these holes (front derailleur cable exit is just below the front derailleur, same as picture. Rear exit is on the end of the chainstay) The hole in question is where the cable exits out of the end of the downtube.

Thanks I'll look into a dremel. Do you know what speed and grit should be used on carbon fibre?

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 1:11 am
by alcatraz
No cable guide under the crank? Maybe your cable guide is broken inside the frame. I haven't wired cervelos but if you don't have an external guide under the crank you will need some kinds of stiff wire channels to support those kind of bends.

I think you will be limited to the grinding stone bits because I'm guessing there arent any sandpaper based bits small enough for that hole.

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 3:34 am
by kkibbler
That looks wrong. The slit looks like it was cut by the cable under tension from the front, resulting in a sharp cable bend up to the FD arm.

I don’t know this exact bike but dollars to donuts the cable should be routed through a guide under the BB.

Or is this frame meant for electronic groupsets?

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 8:02 am
by sennder
kkibbler wrote:
Tue Aug 07, 2018 3:34 am
That looks wrong. The slit looks like it was cut by the cable under tension from the front, resulting in a sharp cable bend up to the FD arm.

I don’t know this exact bike but dollars to donuts the cable should be routed through a guide under the BB.

Or is this frame meant for electronic groupsets?
It would seem that Cervelo S3 (and several other) frames have routing with cable rub anticipated. There is a cable guide under the BB, but the FD cable goes through the rear end of the BB shell (or rather just behind the BB shell) rather than going between the two chainstays behind the BB shell. This seems to be the exit hole of that route.

This is a thread about a similar issue on an S2. Is the hole big enough to fit full shifter housing through? That might be the best option.

--Sennder

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 8:24 am
by Stitchking
iamoutside wrote:
alcatraz wrote:
Tue Aug 07, 2018 12:55 am
I would use a dremel.

How about other front derailleurs? Do they have this problem?

Are you sure the cable routing under the bb is correct. Sometimes the cable guide there can be turned around by mistake.
Hi,

This is my only bike, not sure what you mean by other front derailleurs. I am on a Cervelo S2. The cable routing for the gears runs inside the downtube and out these holes (front derailleur cable exit is just below the front derailleur, same as picture. Rear exit is on the end of the chainstay) The hole in question is where the cable exits out of the end of the downtube.

Thanks I'll look into a dremel. Do you know what speed and grit should be used on carbon fibre?
Please stop working on your bike!!! The cable goes out of the frame under the bb then re-enters behind the bb and up! You are going to destory that frame

Take it to someone who knows what they're doing

Sent from my SM-G935F using Tapatalk


Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 8:30 am
by Stitchking
This is what the cable should look like exiting and the blue line shows correct cable pathImageImage

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Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 1:15 pm
by NiFTY
WHat stitchking said. Get someone else to cable your bike. leave the minuscule carbon rub mark alone. It isn't the problem.

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 1:52 pm
by ms6073
Deleted.

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 10:00 pm
by Stitchking
As an aside you may want to take your bike into your lbs and make sure the integrity of the junction between the downtube and the toptube is still ok. you may have totally cooked your frame. the way the cable is routed in your photo will saw your downtube in half.

Re: Gear cable sawed through internal cable hole Carbon Fiber Frame

Posted: Tue Aug 07, 2018 10:00 pm
by Weenie