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Plastic casing on derailleur cables under BB?

Old 03-05-14, 11:28 AM
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evrythngsgngrn
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Plastic casing on derailleur cables under BB?

Hi,

I was adjusting my front derailleur and noticed that there are two black plastic casings on the cables under the BB that I haven't seen on my other bikes. They are on the cables before the cable guide. I'm wondering what their purpose is. Should they have been over the cable going through the cable guide to protect the cable while in the guide? When adjusting the tension on the front cable, the one casing got stuck at the edge of the guide, so it seems like they're doing more harm than good where they are now.

Any thoughts (this is on a Cannondale SuperSix)?



Thanks.
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Old 03-05-14, 12:20 PM
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THey're just to reduce the cables getting gritty and slowing down your shifting. Sometimes the help guide the FD cable through the frame on carbon bikes. I would change them when I changed cables.
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Old 03-05-14, 12:40 PM
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I wouldn't worry about them if everything is shifting fine. Sometimes they probably help keep things clean, and other times grit may get caught inside the sleeves and actually degrade shifting. But I figure most of the time it's a wash.
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Old 03-05-14, 12:44 PM
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once the BB got so large , the cable guide in the top of the picture was no longer the only point of contact

so those housing liner sleeve sections were added
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Old 03-05-14, 02:42 PM
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^^^good question^^^. Would the cables rub on the frame if those lengths of tubing weren't there? If so, it's probably why they're there, but it's kind of a half fast solution and not something I'd expect to see on a Cannondale. Perhaps it's the wrong cable guide for the frame?
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Old 03-05-14, 03:01 PM
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guess the cost of molding one Custom for their own stuff is not low enough to make it worth while ../

you willing to pay another $100 just to get a custom manufactured BB guide added?
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Old 03-05-14, 04:53 PM
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I use plastic casing (typically housing liner) like that, but it should be located where the cable makes the turn under the BB. It reduces friction and prevent build up of energy drink residue on the cables.
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Old 03-05-14, 05:06 PM
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Originally Posted by Dfrost
I use plastic casing (typically housing liner) like that, but it should be located where the cable makes the turn under the BB. It reduces friction and prevent build up of energy drink residue on the cables.
This is what I was wondering, it seems odd to have it loose where it is, I could see it maybe helping by being over the cable where it goes through the cable guide and makes the turn.
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Old 03-05-14, 05:10 PM
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Originally Posted by Looigi
^^^good question^^^. Would the cables rub on the frame if those lengths of tubing weren't there? If so, it's probably why they're there, but it's kind of a half fast solution and not something I'd expect to see on a Cannondale. Perhaps it's the wrong cable guide for the frame?
It doesn't appear to rub anywhere that they would be protecting, but I'd have to check again.

Originally Posted by fietsbob
guess the cost of molding one Custom for their own stuff is not low enough to make it worth while ../

you willing to pay another $100 just to get a custom manufactured BB guide added?
The guide that is there looks to be appropriate for the BB shell. I'm just wondering if the shop the built the bike added these, or whether they were on the bike as it came in the box, and really if they should be there, or over the cable through the guide.
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Old 03-05-14, 05:42 PM
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Typically , in the bike shop, the frame comes fully assembled in Taiwan drivetrain and rear wheel are on.

there is a carton with small parts in it , pedals, , the front brake and such ..

The front wheel is zip tied along side ,seatpost and saddle is in the box .


if its a new bike , that is probably as it is when shipped .

OP is probably getting antsy waiting for the spring thaw to go out and ride it ..
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Old 03-05-14, 11:46 PM
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Originally Posted by fietsbob
OP is probably getting antsy waiting for the spring thaw to go out and ride it ..
You're right, I can only take so much of the rollers! Winter needs to end...
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Old 03-06-14, 03:06 AM
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Yes, people usually put those on bikes with no plastic cable guides under the BB shell. Not only will the plastic tubes let the cables slide smoothly at the turn under the BB, but they will also protect the paint or whatever finish that's on the BB shell from getting abraded by the cables, and on steel or aluminum bikes with steel or aluminum BB shells they also help avoid the development of corrosion in that area of the BB shell.
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Old 03-07-14, 02:56 PM
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Originally Posted by Chombi
Yes, people usually put those on bikes with no plastic cable guides under the BB shell. ...
Perhaps, but this doesn't shed any light on why they're on this bike which does have a cable guide.

There might have been an intent at some point to put them over the cables where they pass over the cable guide, but it wasn't followed through. You could shift to the large ring or cog and then without rotating the crank or wheel click the respective shifter while pulling on the cable so that it's loose then see you can slide the liners down the cable so that they pass over the guides. Don't know if there will be enough clearance in the guide for the liners but you can try it and see.
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Old 03-07-14, 03:00 PM
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If I understand what's going on in the pic of the BB, it looks like the plastic cable guide thingy might not go far enough in front of the BB to keep the cables from contacting the frame. They "extended" the reach/function of the guide by adding those plastic tubes.....
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