cables rubbing underside of bottom bracket
 

On my newer road bike, there's a plastic piece that runs in between the cables and the bottom bracket of the bike (the underside of the bike) to prevent cables running up against the steel when shifting. I just saw an older Nishiki with the cables housed internally, w/no apparent padding in between the steel and the cable. Is the Nishiki missing something, or is that the way it's supposed to be? If so, doesn't the cable rubbing (when shifting) wear away at the steel? Anything that can be added to reduce said wear? Thanks in advance.

There are a bunch of schemes for routing the cables past the bottom bracket. Most modern bikes use a plastic guide that sits underneath the BB tube. A lot of older bikes would use a guide that clamped onto the downtube and routed the derailleur cables over the top of the BB tube. There are some bikes that have grooves designed right into the BB tube itself and the cables just sit in these grooves. I'm pretty sure that's the way Rivendell does it with some of their bikes.

In the end, the important thing to remember is that it is very important to make sure there is some lubrication that makes the cable slide easily around the bends. When cables get sticky on their way around the BB, then you will have shifting problems. This is a common problem and is addressed by Sheldon Brown in his oft quoted article on "Autoshifting".

Thanks for your reply.

http://superwombat.cdmaforums.com/im...i/IMG_1424.JPG

Looks okay on mine... 1986-87.

Yeah, it does. And that's what the Nishiki looked like. I guess there's something inside the bracket to guide the cables/protect the steel from their friction?

I found that a couple of pieces of PTFE tubing help to lower the friction of the cables where they run under the bottom bracket (see pic)

- Wil

Under normal circumstances it would probably take hundreds of years for the gear cable to “saw” its way through the bottom bracket shell. However do not grease the cables at this point as grit from the road will mix with the grease and form a grinding paste that will cause it to wear more rapidly.

Wil's idea of the tubing is good. Also rubbing some parafin wax (also called canning wax) on the cables will help with the friction and attract little dirt.

Thanks for all the help--the plastic tubing seems like a great idea.

So how often do you shift? Personally, I've never seen one of those plastic cable guides wear through so I suppose the steel bottom bracket shell would be even more durable. Now that I think about it - how much weight could I save by eliminating the plastic guide?

Yes, I had said earlier to lubricate this point, but Dave is absolutely correct in what he says. He certainly knows a lot more about this than I do. The key is to keep this area clean and then no lube will be needed. If your cable gets sticky and causes shifting problems, the real solution is to clean things up and, if needed, replace the cable. A better thing to use than grease would be a light oil like TriFlow or something like ExtraDry, if you must lubricate.

So, Dave, are you trying to say that using a derailleur cable would be the hard to break out of jail? ;)

Yes, to get out of jail you need a brake (break) cable. ;)

Hehe. I'm a little behind. I meant, of course, "the hard way to break out of jail". I guess sawing through a cell bar with a derailleur cable would take forever, but, of course, if you were using a "break" cable it would be much, much easier :D :D :D