Stuck seatpost (I've tried everything)

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  • hey, I know this thread is quite old, but I am just wondering, when you used caustic soda on your steel frame did you pour it in at the bottom bracket or how did you do it?
    I have a stuck seatpost. Tried to cut it out, but turns out it isn't hollow so I am trying to work out another way to get it out...

    Thanks,
    Catrina

  • It's an old thread, but it's an old problem and it's all still relevant.

    Adroit's post covers what you are trying to do.

    Take the BB out, and cut the seat post close-ish to the frame.
    Plug it with something that caustic soda won't dissolve, and fill the seat tube with a strong solution from the BB shell, with the frame upside down.
    After a day or so drain it out, refill and keep repeating until there is no seat post left. The problem is that the alloy will react with the caustic soda and eventually it will cease to react. There isn't enough space in the seat post to get enough solution to dissolve the alloy, and the cheaper, thicker posts take more dissolving!

  • And remember his vet bill induced advice here:-

    And be careful, do this somewhere where pets, kids and the like can't get this stuff on themselves, and keep your skin protected. It does leave nasty burns!

  • "don't ask me how I know this" thread >>>>>>>

  • Here's my story if it helps http://www.lfgss.com/thread116465.html

    Happy to take questions and happy to loan out the tool I made to anyone who can come to Deptford in SE8 to pick it up.

  • Hi all!
    Before you get into any drastic measures, try using Plusgas! I had previously used a bike stand and about 25 minutes of levering the whole bike unsuccessfully. I sprayed plusgas in around the seatpost, let it soak in for an hour, then turned the bike upside down and sprayed it in the seat tube mounting holes and left it for an hour. It then came unstuck by hand.

    I still have half a can if anyone in S London wants to try it

  • Sigh. Might be hitting you up for that plusgas shortly. Just tried to replace my seatpost clamp only to find my seatpost has seized in my frame. I have the added fun/expense of having a di2 battery in the seatpost so trying to avoid pouring caustic soda into seat tube.

  • Yeah that doesn’t sound amenable to blow-torching. I’m in Tooting Bec if you want to give the PG a go

  • 👍🏻


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  • Legend. I'll drop you a PM, could swing by Wednesday/Thursday next week if that suits.

  • Do you know if Plusgas work for aluminium stuck in steel or is it only good for steel on steel? Might need to buy a can

  • Also interested in this^

  • It's just a penetrating oil, can work for either. If it's an aluminium post properly fused into a steel frame you may end up resorting to caustic soda though

  • I've also used equal parts acetone and automatic transmission fluid mixed in a spray bottle, which works better based on my very limited sample size

  • penetrating fluid will only help if its just starting to seize, if its properly stuck it won't touch it

  • This is worth a try, otherwise caustic soda is messy but effective.


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  • I've tried PlusGas on seized alloy posts in steel frames and it's doesn't really do anything when it's actual galvanic corrosion. Used it with success on other seized things though, stuck pedals, rusted bolts etc.

  • Thanks guys, I think I'm probably into caustic soda territory but might give crack-it a go first!

  • Well here we go... thought it was about time I take one of my good bikes out for a spin, so went to retrieve it from a bike box I store it in. Being a nicer bike I not only keep it in a bike box, but even keep the bike box indoors, so didn't expect any unpleasant surpises. Anyway retrieved said bike only to notice I'd left the saddle and post in the frame, which is odd as I normally avoid this, and wouldn't you know when I went to adjust it it wouldn't budge!

    So the situation is I now have a fancy carbon post stuck in an alloy frame, and while familiar with all the usually plans of attack for alloy post in steel frames have never tackled this unholy matrimony of carbon and alloy....

    Does anyone have any ideas please? I'd quite like to save the post if possible, but if it comes to it I'll cut it if necessary. The small glimmer of hope is that the post is quite extended, so it could be worse, and for now I've left it soaking with some Plus Gas, any thoughts from the hive mind greatly appreciated.

  • I would try a slide hammer on carbon. Like the bloke in that YouTube video. Or perhaps clamping in a vice

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Stuck seatpost (I've tried everything)

Posted by Avatar for davhimself @davhimself

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