Stuck Seat Post Removal - Caustic

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  • There's a list of threads here:

    http://www.londonfgss.com/search.php?sea­rchid=4051052

    Strangely for something so common, that search took a little longer... hunt for seat post in the mechanics section.

  • Sorry for dead thread revival. I've got a carbon seat post stuck in my frame, any special advice for removing carbon seat posts differently?
    I've tried WD40 already and had a gander at Sheldons page, but dont think heat'll make a difference fro what I know of physics.

  • Sheldon's worst case method for any seatpost will work for carbon - a hacksaw blade and HTFU, 2 cuts down the length of the post (obviously cut the head off first but leave a cm or two sticking out to grab hold of). Just beware of the carbon sawdust, those nano-wotsits can play havoc with the old pipes... yours that is.

  • I recently used the "caustic soda method" on a pair of stuck Miche (alu) BB cups. Think i had the solution a bit too weak as it took a full week for them to dissolve. Works very well though as it doesn't harm the steel or (apparently) the paint. My paint on the other hand has white stain marks around where the water line was (seat stays, downtube, seattube) but i'm not sure if this is due to the frame being in water for 7days constantly or due to the caustic soda?

    Shoudda made some HTFU strength caustic mix in retrospect as Armourtex is now very tempting...

  • going to use this method, can someone please confirm for me that it wont damage my chromoly frame, bit nervous!

  • going to use this method, can someone please confirm for me that it wont damage my chromoly frame, bit nervous!

    caustic soda will not damage your Cr-Mo steel frame. However it may dull your paintwork where it comes to contact.

  • Hi all, just managed to remove a completely jammed aluminium seatpost from a steel frame using caustic soda and thought would share experience. There seems to be a reasonable amount of misinformation floating around online which might scare people off, but this is a really great way to remove a seriously stuck seatpost, and if you are careful, with no damage to the paintwork (unlike heating).

    First, saw off the top of the seatpost so that about 20mm remained sticking out. Blutack and electrical tape used to block up the remaining hole, and also bluetacked around the lip of the frame so as to keep in any solution that manages to slip down between the frame and the post (this becomes more of an issue as the post dissolves).

    Remove the BB (and just about everything else from the frame) and funnelled a solution of caustic soda (sodium hydoxide pellets) in water (~300g/L) down the seat tube. use blutack to block the chainstays and downtube. I also decided to block up the top tube and the down tube at the headtube end, because I couldn't be bothered to remove the press fits of the headset. Obviously cannot block the top tube and seat stays from the seat tube end as they are blocked by the obstinate post.

    When you dissolve the pellets in water, the solution will heat up significantly. Hot enough to burn so take care. When you tip the solution down the seat tube and it starts to react with the aluminium, everything will get hot, hydrogen gas will be released and bubble out of the bottom bracket shell. If you get close (although be careful not to be splashed by anything coming out of the top), you will hear a fizzing noise. Some solution may well bubble out too - nothing to worry about, just wash away with a bit of water and wipe any off that has ended up on paintwork. The water gets used up in the reaction so more solution will need to be added occasionally. Clear when there is none left as no more fizzing noise and the seat tube will begin to cool down.

    After a day or two, the seatpost should be almost gone. When its finished, it should be really easy to pull out the remnants of the seatpost with a pair of pliers. If it is remotely difficult, plug the hole back up and tip in some more solution and leave for a bit longer.

    Once the whole procedure is done, make sure to wash the seat tube (and possibly the headtube/seat stays really thoroughly with water - otherwise NaOH left in the frame might start to react with your new seatpost as soon as it rains! Vinegar (weak acetic acid) would also be a possibility to neutralise any remaining NaOH, then more water. Finally leaving to dry for a bit (or even better blowing through tubes with compressed air or something similar) then a good load of GT85 in the tubes to avoid rusting the insides away. Good as new for a new post.

    If any caustic soda solution gets on the paintwork and stays there for a bit, it is likely to leave a white residue. This can be removed with water and elbow grease, although I found a bit of acetone made the job a lot easier. In both cases, the paint underneath is slightly dulled but should polish up fine. Generally best to wipe off any solution that spills on to the paintwork.

    As others have mentioned, definitely work covering up to do this job as pretty nasty burns if contact with skin. Goggles and gloves are a must, and probably best to avoid shorts and flip flops. Tip a load of vinegar into the waste solution to neutralise it, dilute it plenty and then tip down the sink. Leave any solids in fresh water in a bucket for a few hours and then throw in the bin. If you treat the whole procedure with a sensible amount of respect, there is absolutely nothing to be afraid of regarding the chemicals you are using.

    Hopefully this rambling post might be of use to somebody, or at least provide further evidence that this is a really simple and reliable way to remove a seatpost, costs considerably less that giving it to your LBS, doesn't require a new paint job afterwards and no risk of damaging the frame.

    Clearly, don't use on an aluminium frame or that will disappear along with your seatpost.

    If anybody has any questions or needs further encouragement, don't hesitate with a PM.

  • I ended up with a hard, white crystalline substance (sodium aluminate, presumably) blocking my seattube after I used caustic soda. I dissolved this with ammonia solution (just experimenting), although I think it may have been the water that dissolved it...

  • Caustic soda FTW. Hot, saturated solution and a hose to stop the frame burning.

    https://dl.dropboxusercontent.com/u/2633­837/seatpost/IMG_0737.JPG

    Will show the whole story once my account lets me start threads

  • Got a frame soaking right now. Also have a couple of small burns on my arms. Seem to be going away pretty quickly though. Hopefully the same is true for the seatpost.

  • Boom!


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  • marsive dredge here.

    went caustic on a super stuck seatpost, few days later and seatpost is gone so all good...the next issue however is I think the residue/byproduct is stuck at the bottom of the seattube?

    when i unwrapped the bottle cage mounts there is clear and hard white stuff filling the bolt holes and seattube. from the top i can see greyish mass, any ideas?

    frame is noticably heavy so there is a pretty decent amount down there.

    attempts to pour water on it to make it react haven't worked..

    i think i will try some cola tonight as that may do a nice acid alkali reaction?

    edit. just noticed @lae mentions a similar thing being dissolved with amonia so that can be the next option

  • Can you get at the blockage via the bottom bracket shell? If so you could use a bent coat hanger or something similar to clear the residue...

  • couldnt get the bb out before unfortunately, that is a different problem for a different day.

    in the end i got a hammer and a long bit of threaded bar with an edge cut into it and hammered through, it was just residue and dissolved once it had broken up. was fucking hard though, really had to hit it to get through!

    all good now. never going to fuck around trying to cut seatposts out ever again.

    the thing i found (in case anyone is reading) is,

    seal up the entire tube, works faster than having it open.

    mix it up really strong, 1 caustic to 2 water otherwise you will be there for ages

    used about 750g of caustic

  • Chemistry/stupidity in action...


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  • I have tried everything, in this order

    Spring the seat post every day with WD40. Did not work

    Drilling a hole through the seat post, putting a metal bar through it and twisting it. Did not work

    Sawing through the post and down into the frame. Did not work

    This means there only one thing left to do. Caustic Soda I realise how frustrating this process can be, so I will make a little video and document the process.

  • could try a better penetrating fluid like plus gas.

    could try heat as well.

    feeding it with diesel is another way and hitting it with a mallet a couple times each day until it moves apparently gets it but takes time

  • I've used a drill bit once it's cut always works

  • Trying caustic as the last resort. We'll see.


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  • I had a triumph today - the seatpost on my current restoration was completely seized, tried heating and lubricating but no joy. Removed the saddle, sawed the seatpost in two and tried hammering the post downwards to at least try freeing it up, but still no dice even after giving it some serious beans with a rubber mallet. Resorted to taking the wheels off, turning the frame upside down and gently dropping the bike - seatpost first - against the floor. After a couple of slams, the post finally budged slightly, but still only slightly. Gave it another go but it went all the way down flush with the top of the seat tube. Cue the next dilemma of getting the post out of the seat tube whilst having no pulling purchase

    Almost gave up and as I was packing up I glanced at an old quill stem! Luckily it just about fitted inside the seatpost and I tightened it up, put my frame in a workstand and after much twisting the little fucker came out!!!


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  • Pic attached to show the importance of cutting down a post before you install it first time round - after 20 years in there it had basically become part of the frame

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Stuck Seat Post Removal - Caustic

Posted by Avatar for wolfenger @wolfenger

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