Question about plastic tubing at bottom bracket

[Fivethumbs]

I have seen plastic tube/sleeve that the derailleur cable is run through around the bottom bracket to prevent the cable from contacting the bare metal of the bottom bracket. Does anyone know what the tubing is called?

[dgauthier]

It's just a length of shift cable housing.

No less a builder than Richard Sachs has said that the housing is unnecessary, except that customers have conniption fits over the idea of shift cable rubbing directly against the bottom bracket.

[Steve in SLO]

Brake cable lining.
If I get a blank stare at the bike shop, I usually go with "You know, the plastic tubing that goes inside the cable housing". That gets it every time.

[oldpotatoe]

I have seen plastic tube/sleeve that the derailleur cable is run through around the bottom bracket to prevent the cable from contacting the bare metal of the bottom bracket. Does anyone know what the tubing is called?

Teflon cable housing. Actually the liner in most der or brake housing, w/o the outer part. See a decent LBS, they should have it.

At same decent bike shop, you may consider having them retrofit a more normal, bolted on, plastic cable guide. Much better idea for index shifting systems like STI/ERGO. The liner gets filled with crud and then the cable doesn't move inside it. I have done the retrofit, drill/tap a hole, thing many times.

[khjr]

At same decent bike shop, you may consider having them retrofit a more normal, bolted on, plastic cable guide. Much better idea for index shifting systems like STI/ERGO.

I've thought about mounting a guide on my bike, not so much to prevent rust (my entire frame is chrome plated beneath the paint), but with the thought that it might improve shifting.

That said, I've figured that the cables are MORE likely to drag on plastic guide, impairing index shifting, since they can get a better bite (thus friction) in the softer plastic material than they would on the metal bottom bracket shell. On my bike, the cable paths beneath the bottom bracket seem pretty smooth...

Thoughts?

[oldpotatoe]

I've thought about mounting a guide on my bike, not so much to prevent rust (my entire frame is chrome plated beneath the paint), but with the thought that it might improve shifting.

That said, I've figured that the cables are MORE likely to drag on plastic guide, impairing index shifting, since they can get a better bite (thus friction) in the softer plastic material than they would on the metal bottom bracket shell. On my bike, the cable paths beneath the bottom bracket seem pretty smooth...

Thoughts?

Generally, metal inner wires on metal BB shells make for far worse shifting(index/click type) than a plastic guide. Campagnolo used to make a metal BB guide which made for really crummy shifting and replacing this with a plastic one made a big difference. The plastic guides are pretty hard, don't seem to get grooved by an inner wire. Campagnolo now makes a nice one with w real long channel for the FD, which ensures the cable won't rub on the BB shell or frame.

[khjr]

Campagnolo used to make a metal BB guide which made for really crummy shifting and replacing this with a plastic one made a big difference.

Exactly the insight I was looking for!

[roydyates]

My winter beater is an early 80s Simoncini with a Cinelli BB that has two metal guides stuck (brazed I guess?) to the bottom bracket. Right now my derailer cables run through these metal guides. Are you saying I'm supposed to have some sort of pastic tubing insert in there? alternatively, are you suggesting grinding off (or removing some other way) the metal guide and replacing with a modern plastic one? As it happens, this bike has downtube friction shifting right now, so it seems to work OK for the moment, but I have pondered switching to STI so I'm curious.

[Fivethumbs]

Thanks for the replies. I found the stuff after searching for "housing liner".

[khjr]

My winter beater is an early 80s Simoncini with a Cinelli BB that has two metal guides stuck (brazed I guess?) to the bottom bracket. Right now my derailer cables run through these metal guides. Are you saying I'm supposed to have some sort of pastic tubing insert in there? alternatively, are you suggesting grinding off (or removing some other way) the metal guide and replacing with a modern plastic one? As it happens, this bike has downtube friction shifting right now, so it seems to work OK for the moment, but I have pondered switching to STI so I'm curious.

No. I agree with one of the other posters that the plastic tubes can be more trouble than they're worth. Also, if the bottom bracket guides on your beater are similar to those on my Tommasini (like two semicircular loops brazed onto the shell), then you'll likely find that there is insufficient room for the tubing to fit through the guides anyway.

Regarding removal of the guides – I’d be loathe to do that, especially on a classic bike (perceived as a beater or not). Based on the recommendations above, I’m thinking of modifying the backside of the plastic guide block to sit over the existing guides on my bottom bracket so that I can give this a try without ruining the frame.

[oldpotatoe]

My winter beater is an early 80s Simoncini with a Cinelli BB that has two metal guides stuck (brazed I guess?) to the bottom bracket. Right now my derailer cables run through these metal guides. Are you saying I'm supposed to have some sort of pastic tubing insert in there? alternatively, are you suggesting grinding off (or removing some other way) the metal guide and replacing with a modern plastic one? As it happens, this bike has downtube friction shifting right now, so it seems to work OK for the moment, but I have pondered switching to STI so I'm curious.

Yes, exactly. Remove the guides if they are in the way, drill, then tap a hole, add the plastic guide. You need to decide if you wish to do this surgery to the frame BB shell. Friction generally doesn't care but the precision of index shifting does.

[Tom Matchak]

Some earlier posts have advised that adding a plastic cable guide under the BB requires drilling a new hole AND tapping it to accept the anchor bolt. If you use the right style of cable guide, there's no need to tap this hole, which would be prone to stripping with only a couple of threads.

Shimano makes a cable guide model SP-18-T, which is shown in the linked photo. This requires only a 5/16" hole in the BB shell. It doesn't show in the photo, but there's a short conical protrusion on the underside, in line with the screw, which fits into the 5/16" hole. As the screw drives into the guide, this protrusion expands and locks the unit into the hole.

http://www.flickr.com/photos/34156114@N05/3429237676/

The second hole shown in the guide isn't used for mounting. I always drill a second hole, aligned with this empty hole in the guide, as a low-point drain for the frame.

IME this particular Shimano guide isn't always easy to find, as most places are quick to offer the other style (in dark brown plastic) that attaches via a M5 bolt in a tapped hole. But, if you ask for it by the model number, they're out there.

[roydyates]

No. I agree with one of the other posters that the plastic tubes can be more trouble than they're worth. Also, if the bottom bracket guides on your beater are similar to those on my Tommasini (like two semicircular loops brazed onto the shell), then you'll likely find that there is insufficient room for the tubing to fit through the guides anyway.

Regarding removal of the guides – I’d be loathe to do that, especially on a classic bike (perceived as a beater or not). Based on the recommendations above, I’m thinking of modifying the backside of the plastic guide block to sit over the existing guides on my bottom bracket so that I can give this a try without ruining the frame.

It sounds like we have the same guide bracket. If you ever figure out how to overfit a plastic guide, please send in some photos. Thanks!