Friend bought a bike and the seatpost is seized in the frame – its a trek 2.3 road bike from a few years ago. Looks like it could be a carbon post.

Even the bike shop says the post is seized, but is this possible for carbon in alloy

Yes carbon can undergo ‘galvanic’ corrosion 🙁

I think I read somewhere that if the incorrect grease is used the resin in the carbon can swell, which would then make it pretty difficult to remove.
I’m not a materials specialist though so it could be rubbish.
Someone will be along soon to set us straight.

do wear a mask when cutting it out and work outdoors if possible.

galvanic corrosion – aluminium and graphite (ie carbon fibres) are quite a way apart in the galvanic series with the aluminium being the one that will corrode. Epoxy resins can swell but epoxy is pretty resistance to mode chemicals – some lubricants and cleaning solvents can have nasty ingredients in though. I suspect it is corrosion.

Probably going to have to be a case of carefully cut the seat post out.

Use water a lubricant and to keep dust down and don’t cut all the way through the post to avoid scratching the inside of the aluminium frame (as this can cause failure later on). Use a new fine pitch hacksaw blade and leave as much above the clamp as possible to use for squeezing/flexing the post inwards when the cut it almost though.

Very possible. My alloy post bonded solid into carbon frame. Hell of an effort to get it out and almost was going to cut it out. Tried all kinds of stuff, though I lacked a big vice to put the post in and rotate the frame as one trick is (not sure it’s wise with a carbon frame anyway).

What seemed to work best was soaking in some snowboard/ski base cleaner. Basically a citric acid fluid. I then started getting tiny movement with a lot of twisting force, and just kept trying to rotate it. Took hours, a lot of squealing noise and a hell of a lot of effort and swearing.

Now I don’t leave the post in the frame apart from riding. Also, coat the post surface with carbon assembly paste. It helps protect against this and also reduces the torque required when clamping carbon.

And yes, in my case the alloy corroded. Surface of the post was very corroded. Frame was good.

Yep, carbon post in my winter bike is seized solid. No grease or inappropriate substances, just seized. Ought to sort it really.

Salt spray from the road will have caused it at a guess.

I had one like this recently – Easton carbon post completely seized in an alloy frame. It took quite a lot of brute force to get it out, so much that I’ve now made a special hydraulic stuck seatpost removal gadget 😉

There’s a carbon fibre freeing spray called something like Carbomove, sorry can’t remember exactly. I had the same issue with a carbon post in an alloy frame, used loads of the stuff, soaked overnight and the post came out with a bit of pulling. Cleaned the inside of the seat tube with an appropriate stiff brush and is now fine. The issue was the alloy not the carbon.

This stuff – worth a try before you destroy a carbon seat post unnecessarily and worked for me.

I recently had this on my CX bike. Boiling water poured over the frame sorted it in the end after a few days of soaking it with WD40.

Thermal shock could work well (the hot water trick above). The aluminium will conduct well and expand quickly.

Doh, I thought You’d be safe with a carbon post.

What about carbon post carbon frame?

so much that I’ve now made a special hydraulic stuck seatpost removal gadget

See,that right there is what I like about Ben’s posts.

If in doubt ,make a gadget 🙂

D0NK – Member
Doh, I thought You’d be safe with a carbon post.

What about carbon post carbon frame?
Should be okay, same/similar material.

Still use carbon paste however. Less torque required to clamp enough to stop it slipping, so less likely to over torque and crush the stuff.

lots of WD40 then hot water on the frame will expand the seat tube and eventually free it up. Fit an old saddle and give it some abuse. Worked for my carbon post in steel frame.

It’s not galvanic – there is no chemical bonding, it is however frame corrosion that causes minute imperfections in the surface of the seat tube that increase friction, nothing serious, but annoying.

Aluminium oxide takes up more space than aluminium so as the oxidation builds up, the gap is filled and the post seizes in the tube or vice-versa.

With a carbon post in a carbon frame, do up the pinch bolt with a torque wrench then undo it by hand and be amazed at the force required to achieve the recommended torque.

See,that right there is what I like about Ben’s posts.

If in doubt ,make a gadget

There’s a corollary – even if it takes longer to make the gadget than the job itself takes, still make the gadget 😀