Case and point, I found an article on Cyclocross Magazine's website covering a frame modification which allows you to run a continuous piece of derailleur housing from the top tube, down to the rear derailleur. I'm game, I thought.
The modification was pretty straight forward, requiring you to drill out the cable bosses on your seat tube. You needed to open up the cable stop just enough to allow the boss to act like a guide for the housing. Yeah you could not drill out the boss and just zip tie the housing to the frame but that wouldn't look nice and stock, would it?
- 3/16" drill bit
- cordless drill
- celeste touch up paint
- small file
- housing, black Shimano SP41 pre-lubed derailleur
- ferrules, Jagwire brass 4mm
I first used the calipers to confirm the outside diameter of the housing, 4mm in measurement. Next I cut a new length of derailleur housing, basically matched the lengths of the upper and lower (at derailleur) including the new run which would be where the exposed cable run is shown in the photo to the left. This length will get you the needed 36cm of housing loop from the rear derailleur to the first lower boss on the seat stay. 36cm will get you better rear derailleur shifting on any SRAM group.
With the 3/16" drill bit I carefully drilled out the cable boss. Access to the drilling point should be made from the 'cable exit end' of the boss. Slow and steady is recommend as you do not want the bit to jump off the boss and score the carbon frame.
After both bosses on the seat stay were drilled out, I used the small file to smooth out any sharp edges the drill bit may have created. With compressed air, I cleaned out the newly drilled bosses of any aluminum chips from the drilling followed by touching up the drilled bosses with celeste colored touch up paint. Be sure to shake up the bottle of touch up paint really well along with stirring the paint with a tooth pick. This ensures that your paint is evenly mixed and looks like the Queen's Green and not blue-turquoise- a result of not mixing it well enough which I found out on the fork of my Oltre this summer.
Install the new piece of housing when the touch up paint has dried. The rear derailleur cable was practically new so I reused it. (Delta Duracote Teflon shifter cable.) Before anchoring the rear shift cable, inspect the alignment of the derailleur hanger. Some hangers will get slightly tweaked inward from cross chaining and also OEM hangers are typically softer and easier to bend than say an aftermarket one from Wheels Manufacturing. Also check your alignment of the jockey pulleys under the high and low cogs on the cassette. These are all CYA items you need to check before pinning on the first number of 'cross season.
Anchor the rear shift cable, adjust the cable tension as needed. Now I have a semi-sealed rear derailleur housing. This should keep the rear shifting smooth during those days of muck and slop at the races. Thanks Cyclocross Magazine for the idea.