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Originally Posted by climber7
(Post 12633747)
http://www.parktool.com/blog/repair-...osts-and-stems
this is what i was thinking of...from the second paragraph in the link above: "When inserting an aluminum post into a carbon frame, it is important to apply a barrier between the two surfaces. This is also true when installing a carbon post into a steel or aluminum frame. A 'galvanic reaction' occurs between the two different materials and this acts to eventually bond the post to the frame. Use a light coating of grease, anti-seize, or other lubricant to create a barrier between the two surfaces." i guess i was mistaken in the sense that carbon paste is more for friction (and maybe just for carbon on carbon??), but it seems like the important thing is to get something in there to prevent bonding. J. |
Originally Posted by JohnJ80
(Post 12634015)
That would be surprising to me. I believe a galvanic reaction requires two metals not metal and plastic.
J. My LBS told me to put a bit of grease around the top of the post to seal out water. The post itself was dry. I mostly did keep the top sealed, and didn't ride in wet conditions very often, but it didn't prevent the corrosion. |
Originally Posted by JohnJ80
(Post 12634005)
That doesn't seem right. Are you sure there is no grease or lubricant in the seat tube?
At least when I went to an AL seatpost in my carbon frame, all the slipping stopped. J. |
Hmm. Interesting. I can see some interaction between the AL and the C seatpost, but I don't think it would be galvanic. Some other kind of interaction.
J. |
i'm just posting this because i find it interesting...i realize we're way past the OP's question. from Boeing (who, i assume, know what they're talking about):
"Fiber-reinforced plastics are corrosion resistant, but plastics reinforced with carbon fibers can induce galvanic corrosion in attached aluminum structure." http://www.boeing.com/commercial/aer...7/corrosn.html you learn something new every day. |
Originally Posted by climber7
(Post 12635724)
i'm just posting this because i find it interesting...i realize we're way past the OP's question. from Boeing (who, i assume, know what they're talking about):
"Fiber-reinforced plastics are corrosion resistant, but plastics reinforced with carbon fibers can induce galvanic corrosion in attached aluminum structure." http://www.boeing.com/commercial/aer...7/corrosn.html you learn something new every day. J. |
Yup. Friend of mine had a Specialized Epic from the early/mid-90s that was carbon tubes with aluminum(?) lugs. It eventually disintegrated where the two materials met. It's very important to isolate the two materials by adding something like a layer of fiberglass between the carbon and the metal (when building a frame). I think Specialized started doing that partway through the production cycle for that bike.
I'm not sure if any of the people making carbon posts go to the trouble of adding this "passivating" layer, so it is a good idea to regularly remove and re-grease a post that is being used in an aluminum or steel frame. The problem is worse if you live near the ocean vs. inland and worse if you ride during the winter in parts of the country that use salt on the roads. This is not a problem for titanium frames as carbon and titanium are adjacent in a published galvanic series in sea water [Jones, Principles and Prevention of Corrosion]. |
pipe compound is a thread sealant with teflon. inappropriate. get off your couch and get some carbon assembly paste.
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