After four years I decided to raise the aluminum Thompson seatpost on my steel Vaya. I had, for some foolish reason, believed that the finish and machining on the seat post would prevent it from seizing and I was very wrong. It is utterly stuck.

I understand that a strong lye solution will dissolve aluminum while leaving the steel totally unaffected and plan to remove the bottom bracket and protect the paint with tape and a plastic sheet while dropping the lye solution down between the post and tube like penetrating oil. Goggles and gloves will be worn.

Does this sound like a reasonable plan? How long is the process likely to take? How sensitive is the paint (powder coat?)?

Any advice is appreciated.

And I have a tub of anti-seize ready if I'm lucky enough to need it for a new post.

Very FAQ... A plethora of past posts on that topic, I wont repeat them, look them up in the archived posts ..

Mea culpa. Should have checked. I have added a few questions to an earlier post.


This issue is causing me stress. I don't want to bugger it up.

First do the reasonable things. Remove the bottom bracket, flip the bike upside down, and spray an entire can of PB blaster down into the seat tube. (Tape up any holes at the end of the seatpost.)

Let it sit there a week, refill if necessary. Come in EVERY DAY and give the seatpost many many tap taps from a hammer. All of the way around the seatpost from every angle. I bet if you let it sit there and do that long enough it'll come off.

When you're ready to take the post off, you can either drill a hole all of the way through it and stick something in there to twist while you're lifting, or you can just grab the post with a vice and twist the whole frame.

Come back and report then.

Start gentle, when that doesn't work then think about using lye.

The lye won't work like penetrating oil. You have to get a large amount in there and dissolve the post all at once from the inside out.

The lye method truly is a last resort solution (no pun intended). I try everything else first (including the hacksaw approach).

.
...PB Blaster is OK as a penetrant, but what I use now is a 50/50 mix of acetone (paint aisle) and ATF (auto parts aisle).

It's just better enough for stuff like this that it's worth mixing up and using.


The only other tip I have is to find someone with a large bench vise firmly attached to a solid post or workbench that is in turn bolted to the wall or floor. Remove your wheels, replace with either bare hubs or axles double nutted into the dropouts/fork ends.

Find at least one other person to help, and once you've affixed the end of the post in the vise in such a way that you have clearance to turn the whole frame, one guy pushes on the frame to twist it on the post, the other pulls on the frame in the direction away from the vise.

I have done 50 or 60 stuck posts for people at the bike co-op using this method, with only two or three failures. It's hard work, but well worth it if you can avoid the lye thing.

Yes this topic has been covered several times in the past, my only addition to the above is with the bike upended I use an old saddle that you can find anywhere & clamp that as hard as possible in the vice to destroy it, (it may save you the seat post) then proceed

Kroil.

Kroil is so effective, it'll even works its way out of its own sealed container. I have an unopened container with an oil ring around the bottom.

I chickened out and paid an experienced mechanic to do it. Well worth it. I really didn't want to mangle the frame and had a bad feeling...

Toronto, huh? I just happened to be standing in Malcolm Munro's shop a few days ago when he was showing somebody a corroded seat post he had extricated from a frame. That wasn't you, was it?

I can run but I can't hide. Yes. It was me. And it was a nice Thomson post. Broke my heart!


And describing Malcom as a 'mechanic' doesn't paint an accurate picture. What a remarkable place and talented, eccentric guy. I'm glad I discovered him.

Well, I was standing between you and Malcolm when he showed you the post. It was the first time meeting the guy. I was there with a guy I'm helping with a project and we were there to pick up a battery bracket Malcolm is fabricating for it.

This is the shop we're talking about: Biseagal | Our History