kingfishr

I recently purchased a circa 2002 Colnago C40 B-stay non-hp with Geo paint, a grail bike for me. Overall the frame is in good condition, but the brake cable guides are badly corroded and I had to destroy the steel ferrules to the derailleur adjusters in order to get them out. The same on the back derailleur guide. The rear dropouts look fine. The previous owner lived in Miami, so I am hoping that the corrosion was caused by the steel ferrules against the aluminum guides and excess exposure to salt air. Better this than galvanic corrosion between the carbon fiber and the aluminum. Has anyone else ever experienced any similar corrosion and know the cause? I have cleaned it up as best possible and sent it to a paint shop for a new clear coat and whatever touchup can be done to the missing paint. But would be good to know if that will be enough,

rpenmanparker 

Good news is that ferrules that come in new cable kits these days are plastic. if you can get on top of the corrosion you already have, it shouldn't be getting any worse due to further contact with a dissimilar metal. Jagwire Pro Road for instance.

kingfishr

Thanks, good idea!

BoJaffa

That corrosion does look fairly severe for sure.. Maybe ask in the Mechanics forum as those guys have a lot of knowledge and may be of assistance to you. Nice frame by the way. I have an '01 Trek 5900 and the ferrules on the top tube show corrosion as well. Probably from sweating too much.

BillyD

Yup. Might also check out the Classic & Vintage forum, they're great at restoring bikes.

kingfishr

While they might appreciate a 10 year old CF frame, I follow the C&V forum and 99% of the content is about steel. Maybe in 50 years

Carbonfiberboy 

I had the same thing happen with my cable stops on a '99 Trek 5200. Trek replaced them twice on warranty. I live near saltwater, but it's also possible that sweat was the conductor. For sure it's dissimilar metal (galvanic) corrosion between the carbon and the aluminum. They're far apart on the galvanic table. I don't know why this doesn't happen more frequently to carbon bikes. It would help if the manufacturer would use an insulating pad or dot of resin as an insulator. Or use carbon guides, more better.

kingfishr

Well that is kind of what I am trying to understand. The cable guides are rock solid on the frame. If the galvanic corrosion had occurred between the CF and the aluminum I would expect that they would have loosened. Instead it was the steel ferrules from the brake wires that were completely stuck inside the cable guides due to the corrosion. So I am hoping the reaction was between the steel and aluminum in combination with salt air...

Did the cable stops on your Trek loosen?

3alarmer 

...my understanding of Galvanic corrosion is a little limited, but if you look at the chart above, you'll note both the positions of the various materials in terms of potential, and the direction of the anode material, which is where you'll see the evidence of corrosion. Are you certain your cable ferrules were of steel ? A lot of them are some sort of plated brass, and you can even get alloy ones now.

I think what happens in this case, is that the potential just sets up the corrosive action at whichever point you have dissimilar materials that are farthest in the direction of the anode in contact at the junction of the three. (But I own nothing similar in construction using those materials.)

So in this case, the contact between the alloy guides and the cable ferrules, which has a tendency to happen slightly anyway, might have been further accelerated by the carbon frame tubing. Plastic ferrules sound like the best solution, but a light application of an anti seize with zinc in it as the sacrificial metal would probably work too.

I think...............................maybe..........................not promising anything here.

3alarmer 

...I have no idea at all what will corrode if you eliminate the metal ferrules and just go with plastic ones.

We used to have replaceable zinc ingots on the exterior hull of my ship in the navy, which were periodically replaced by divers.
The sacrificial anodes (the zincs) slowed the corrosion of the steel hull. I'm not sure how you would do similar with a cable guide...zinc wire ties maybe ?

kingfishr

Yupp had zinc anodes on my Yamaha outboard, was wondering if there was any way to achieve the same result...
If the cable guides were properly mounted with an insulating substance between the CF, then ideally nothing should corrode.