Replacing Shimano 105 gear cables on Cannondale Caad 12

[tunybgur]

Last year I had a gear cable break at the selector lever for the rear derailleur causing my bike to be stuck in high gear.
I had it replaced by a bike shop and decided to carry out preventative maintenance myself each year to save this happening during an event.....didn't fancy tackling a 12% grade stuck in high gear!
I have stripped out all the cables, inners and outers, and have started replacing them with Shimano optislick cables (are these ok, or are there better options?)
The problem I have is that there appears to be some PTFE tube covering some of the old inner cables, and I can't get any info on this from Cannondale, and it's not shown on their parts lists.
I know the purpose of this tubing is normally to reduce friction and can be used as a cable guide for internally routed cables.
There is a small plastic cable guide bottom bracket under the crank where the cables come through and are routed around the crank. The front derailleur cable had PTFE tubing over the inner cable where the cable went around this bracket, but the rear derailleur just had bare cable (this was the cable replaced recently).
Does anybody know what the correct protocol for using this tubing is in this area? Is it to prevent wear of the plastic bracket, or just to reduce friction? The front derailleur is original as received from Cannondale so it must have been a factory fit....is this essential for proper operation?
Hope someone can help....don't want to take it all apart again to fit a bit of tubing.

 

[Yellow Saddle]

That tubing is used wherever the cable slides over a guide of sorts. It isn't PTFE though. PTFE is extraordinary heavy and the tubing you are talking about (I'm guessing) is light and flexible. Doesn't matter, it does the same job.

 

[tunybgur]

So is this a standard fit on the inner cable around the guide, or around corners in general?
Should I fit this tubing on both cables? It was only fitted on one when i took it apart.
Does Shimano advocate using this tubing on their cables?
That's what I'm trying to find out, Cannondale doesn't show it on their parts list but they must have fitted it originally?
I'm a bit confused

 

[Yellow Saddle]

Don't be confused. Work from first principles. The purpose of those tubes is to reduce frictions around corners where normal outer cable (cable housing) cannot be fitted. Be guided by that. I can't envisage the exact scenarios you are concerned about. A photo will help.

Shimano doesn't advocate the use or non-use of those linings. It isn't up to Shimano, it is up to the frame design.

 

[tunybgur]

This is the cable guide, the front derailleur I'm happy with the tube, but the rear goes through a tight double bend and is a bit tighter to pull with the tube fitted, but without the tube over the cable will the cable wear into the plastic guide?
It wasn't fitted by the guy who last replaced the broken cable, but that might have been because of the difficulty level of fitting the tube without also slackening the front derailleur cable....tried it myself and had to replace the guide after breaking the front leg off, it's quite fragile until it's fitted in place.

 

[Yellow Saddle]

OK, I see what's going on there. No, the tube is not necessary. The RD cable won't wear through the guide. All bikes with BB guides have plastic or metal guides and wear is never an issue. Omit the tubing if it gives you hassles.

Plastic tubing in internal cable frames is there only to make cable replacement easy. Without the tubing you have to fish around to get the cable end to come out at some or other small, obscure aperture. With a tube (flared at both ends so itself doesn't go AWOL), it is just a matter of pulling out the old cable and pushing a new one in. That plastic guide of yours is smooth enough, so no need for a HDPE tube. Yup, it is made from the same stuff you buy milk in.

 

[tunybgur]

Thanks for your advice, you are obviously very well qualified to give it.
The one mystery is why the original front derailleur cable (centre guide) had plastic tubing over it as received as a new bike from Cannondale, and it's not shown in the parts list?
My theory is that it might be to protect the cable from road dirt which could create a grinding paste around the cable, it does get very wet and gritty in that area.
I think what I will do is retain the tubing over the centre derailleur which is quite exposed, not use the tubing on the rear derailleur as it increases the friction because of the tight double bend, but I will make a simple flat plastic cover over the guide and tape it in place to try and keep most of the grit out (seems like an obvious thing to do?).
My last question is whether or not to use a bit of silicon grease on the cable/plastic guide interface, or leave it dry? The optiflex cables are supposed to be PTFE coated so maybe leave it dry?
Thanks for your help

 

[Yellow Saddle]

Leave it dry. Never grease cables.
Here's another guideline. If the tubing you use has any chance of allowing water to run down the cable and collect at the bottom of a loop in the tubing, you are better off leaving it out. If both ends of the tubing are hidden in a way that you can't get drip-down, then tubing will probably work, given that you've adhered to rule one above.
Without the bike in front of me, that's really the best advice I can give.
Go ahead. You can do it.

 

[User6179]

The one mystery is why the original front derailleur cable (centre guide) had plastic tubing over it as received as a new bike from Cannondale, and it's not shown in the parts list?

The plastic tubing I have only seen when the cable goes through the BB and out a hole in the frame below the front mech, the tubing is to protect the frame as much as protect the cable as it would rub against the hole as you change gear, provided the cable is not touching anything but the guide then I don't see what use it would be.

 

[tunybgur]

I'm coming to the conclusion that it's best not to use the tubing at all and see what happens over the next year or so....I've got lots of scheduled events apart from riding to work and back every day so It will get plenty of work.
I must admit for the first few months of owning this bike I was always adjusting the shift cables, they never seemed to hold a setting.....maybe that was the soft tubing giving way?....but I was also changing the cassette quite often (needed a 32T to get up Col d'Izoard in 2017....I know, bit of a wimp)....

 

[Ming the Merciless]

Blimey sounds complicated. Think I will stick with full length external cables. Five minute job to replace cables.

 

[User6179]

Blimey sounds complicated. Think I will stick with full length external cables. Five minute job to replace cables.

The cable on my new bike goes inside the down tube then through the BB and inside the chain stay, I cant wait till it snaps and I have the pleasure of changing it.

 

[tunybgur]

I can see your point....but take a look at the latest carbon bikes...everything moulded in and flowing, even the brakes....they really are beautiful works of art.

 

[Ajax Bay]

Last year I had a gear cable break at the selector lever for the rear derailleur causing my bike to be stuck in high gear.

take a look at the latest carbon bikes...everything moulded in and flowing, even the brakes....they really are beautiful works of art.

to Cycle Chat.
Is changing a gear cable on the road an 'art' or a 'science' with internally routed cables?

 

[tunybgur]

Ha! A good question.......not something I would like to attempt mid race, hence the preventative maintenance.