Carbon frame and alu seat post. Alu post is well corroded.

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  • Carbon frame and alu seat post. Alu post is well corroded.
  • medlow
    Member

    I started to strip down my carbon gravel bike to migrate the parts to a new frame.
    The seatpost was stuck in pretty well.. I eventually got it out to find the alu seat post has corroded which was the cause of the stuckness. The post when cleaned up has large areas of aluminium crumbled away.

    I was surprised at this considering its not been in that long and I’m a fair weather rider mostly.

    I have new carbon post ready to be fitted to my new alu frame which is the same material pair in close proximity to each other. The seatpost is already a tight fit and carbon paste makes it too tight..

    Will white lithium grease be a good substitute for a carbon post in an aluminium frame? I’m concerned about this corrosion now I have experienced it in person. If I suffer post slip then I may rethink but it should be good yeah? Will I die?

    timba
    Member

    You can get smooth CF paste, I use Motorex Carbon Grease, which will address corrosion and sizing problems

    paton
    Member

    At about 6:20 in

    medlow
    Member

    Yeah that post he showed, had the same powdery corrosion as my alu one.. I suspect that inside my carbon frame I have the same.
    Interesting stuff.

    It’s obvious that regular inspection is needed. I have never suffered this issue before in 15years so was very surprised. But then never owned anything carbon until 2years ago.
    I’ll slap loads of lithium on my new post and frame and inspect regularly.

    patagonian
    Member

    I was under the impression that you never put grease on carbon………..

    Premier Icon deadkenny
    Subscriber

    Carbon assembly paste is designed for carbon. It’s grease like stuff with small particles that provide friction. Never had an issue getting an ali post in a carbon frame using the stuff and the paste means you don’t need to clamp as tight.

    As for the corrosion, it’s galvanic reaction between two dissimilar materials. Carbon assembly paste helps reduce it, but I’ve found it can still happen. Just that with the paste the seatpost didn’t bond to the frame as severely as it did originally without the stuff where it took a hell of a lot of effort, tools, vice and swearing to remove it.

    Also a few post manufacturers recommend using the paste for ali frames also. There are differences between types of ali which can still result in a reaction, plus the paste help reduce the clamping force required.

    Premier Icon Jon Taylor
    Subscriber

    I have this same issue on my MTB; alu dropper and carbon frame.

    The fit is too snug for a carbon grip compound, the particles make it jam on the way in!

    these are the replies I had last time it got a bit stuck after not being moved enough

    Anti-seize for alu seatpost in carbon

    5 months on, I hadn’t moved it and it got pretty stuck again…

    medlow
    Member

    Yeah.. jon, same here, my new frame and post are really snug, too snug that carbon paste with lumpy bits make it too tight..!
    I’ve lubed it up proper with lithium grease as that’s all I have in my box.. let’s see what happens.
    Either it slips, it still corrodes or works just fine.
    Probs I’ll add a seatpost removal as a regular job to be sure..

    Premier Icon Poopscoop
    Subscriber

    timba

    Member
    You can get smooth CF paste, I use Motorex Carbon Grease, which will address corrosion and sizing problems

    This is absolutely the stuff to buy if you have a carbon frame or parts.

    I bought the paste with the grit in and it scratches the hell out of stuff and is no good on tight fits.

    The Motorex solves both issues and it will last you for ages once bought.👍

    Premier Icon Poopscoop
    Subscriber

    ^^ The packaging is different (the graphics on the tub etc) but the description sounds right.👍

    Basically like a thick, clear “glue” and not gritty at all.

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