Doug,
As always, I agree with most if not all of what you say. In this particu lar case though; there are a few things that will prevent the typical pr oblems that can accompany top cable guides. Placement and then brazing m ore than just the bottom of the guide to the BB shell is one good practi ce. The other is don't use any other than Campag. guides; all others I'v e seen are inferior to Campag. bits. Proper prep of the bb surface AND t he cable guide surface are critical to good results.
As far as painting them goes; I've found that the application of the pri mer is the critical stage. If not done properly, the metallic coats and top coats have no chance to get in there with candy colors. Regular colo rs respond better as well when the primer goes on correctly.
Since top cable guides are part of the original specification of a numbe r of vintage bikes; it's best to know how to deal with them when it's ne cessary for those who require it. It can be done to where they do work p roperly and last forever and the paint is perfect as well. I only mentio n this so that people don't feel that they should change them over when it's not appreciate to do so.
Brian Baylis
La Mesa, CA
Takes practice, but it can be done.
The real problem with top of the bb cable guides is that, even if they a re properly brazed on, they can eventually pull off. The corner of the fro nt derailleur guide is particularly subject to this problem. It is a natur al stress riser with all the force of the cable pull concentrated on one po int. This is the primary reason framebuilders stopped offering them sometime in the early 80's I think. As a painter, I have a little box with these braze-ons I have kept that have come off of a variety of frames. I coul d see when they were off that the brazing was complete. So it is not an i ssue of brazing quality but of faulty design. A lot of tension can be put on the cable if the derailleur isn't inclined to move. I've also seen a lot of
bent ones from strong cable pull. My guess is that about 5% have failed .
A customer is going to demand a redo which might involve a repaint and reassembly - which can be several days of lost work. I switch all top mounted guides on my frames if they came in for a repaint. Fortunately there were only a few I did that way in the 70's. I was influenced by m y 69 and later Hetchins (that used under bb guides) and I really liked the cl ean lines of a cable going underneath. As already mentioned, it is impossib le to get paint properly between the top mounted boss and the tube and if i t is a candy color, that looks really awful.
Doug Fattic, not wanting to do free work because of a faulty design in Niles, Michigan, USA
On 10/20/08 8:37 AM, "classicrendezvous-request@bikelist.org"
<classicrendezvous-request@bikelist.org> wrote:
> Date: Sun, 19 Oct 2008 22:59:23 -0400
> From: marcus.e.helman@gm.com
>
> Why did framebuilders start running cables under the bottom bracket?
It
> seems to offer no advantage. I have one bike with the cables run on t
op
> of the BB, and one with the cables running underneath. There is no
> difference in shifting that I can tell. Maybe it's just esthetics.
> Personally, I prefer the more traditional top of BB treatment.
>
>
> Wondering,
> Marcus Helman
> Detroit, MI