Amt0571

I have this bike that I want to paint as explained on another thread. First issue is that the seatpost is extremely stuck, I presume, from galvanic corrosion between the alu seatpost and the steel frame.


I'd like to save both, the frame and the post if possible. If not possible, I'm willing to sacrifice the post.

The post, as you can see has a flat surface on top, ideal for holding it into a vise. I was thinking about putting it in a vise and using the frame as leverage. However, I'd like to know if someone with more experience feels like this is viable or I could damage the frame doing this.

Thanks!

Rolla

That can certainly be done, and is often what it comes down to. But see if using generous amounts of PB Blaster, allowing the frame to sit for a day or two between doses, will do the trick. I've also seen people lop off the seatpost above the frame and then use a hacksaw blade to saw vertically through the embedded section of seatpost until they hit the inside of the seat tube, and then crush or roll the seatpost to make it skinny, but it's a process I wouldn't want to do myself. The toughest case of a stuck post I've encountered was conquered by PB Blaster and a vice. It took soaking the post for a week prior to the vice, and the saddle was sacrificed in the process. I don't know if the flat section of that seatpost will hold it securely in the vice under the kind of torque that may be required to twist the frame.

xiaoman1 

Google "Stuck Seatpost" BikeForums...there has been a lot of discussion on this topic.
PB Blaster is a great way to soak the post and frame "before" trying to "wrench" it of with the help of a vise.
Others use a mixture of ATF with acetone....best to use the least intrusive measures before resorting to brute force....be patient.
GL, Ben

Iride01 

Have any additional mounts been added to the seat tube that might have put a screw through the seat post?

Take the saddle off and you might figure out something better to attach some thing to give you more leverage to twist with and avoid scratching the post.

Also take that bolt out of the seat tube completely and get something in between there to wedge it open more. If you get a gap opening there around the seat tube and post, then more penetrating oil will penetrate (duh). I suggest Kroil. But others work too.

Amt0571

Thanks everybody. On my other thread about painting the frame someone suggested a good idea.

Since I'm going to repaint the bike, I can afford to ruin the paint job, so I can also use a torch to get it loose.

I'll try with penetrating oil before anyway as its easier and I have lots of time to let it soak.

Will it be better to put the oil from the top of the seatpost? Or from the bottom through the bottom bracket?

SurferRosa

I'd use a shot glass full of equal parts ATF and acetone. And let it sit a week. Try freeing it, then do it all over again. Patience and penetrant usually win.

Amt0571

But where do I put it? From the top? Or through the bottom bracket?

sch

Since only a few ml of penetrant is needed for the top, any more runs down the outside, do that daily for 3-5 days.
If not loose then invert frame and pour from BB, again letting each bolus sit for a day or two an ounce or two. This way you get
penetrant a good ways into the interface.

SurferRosa

Usually the top is too tight, so through the bb. But, in this case, it looks like you could do both.

andrewclaus

Don't bother with heat. Aluminum expands more than steel.

I recently removed a tough one by deforming the post and vising it.

In recent experience, an excellent penetrant is DOT-3 brake fluid. It'll ruin your paint, but that's not a concern here.

First, though, try impact and torque on a sacrificial saddle. Hit the nose of the saddle with a mallet (safely). If the saddle trick doesn't work, try a large (14 or 18") pipe wrench. Lay the frame flat and stand on the wrench (safely). If you can get it to move at all, it'll eventually come out.

Mad Honk 

Like Surfer I use the atf- acetone mix from the bottom side. I use about four ounces so it fills the inside of the post and covers the section so it has plenty of room to fill the space between the post and seat tube. I use a four foot steel 1' X1' tube with two clamps to hold my 14" adjustable wrench over the post flats for purchase. Then pry the top tube and four foot bar apart. be sure to do this above a small bucket to catch the mix that will pour out of the tube when they split. I work them apart with the seat post just inside the bucket. Smiles, MH

Bimmer69

Long interesting read here with nuclear option ideas
​​​​​​HackBlog: The Seatpost and the Damage Done

LV2TNDM

That's a beautiful post and it would great to save. But saving it will most certainly not be possible. All depends.

Freeze-thaw cycle would be a good idea. It would be nice if you could allow an acid to work its way down through the corrosion to remove it. Since the corrosion is all oxides, it should be much more vulnerable to the effects of acid than the underlying metals. But getting it in there is the challenge.

If you could force a plug (cork, etc.) just to the bottom of the seat post to seal it and THEN introduce solvents/acids, etc from the bottom bracket with the frame upside-down, this would better encourage these compounds to work their way down between the post & seat tube.

That said, it's the seat post that's usually sacrificed in the removal process. Usually, the saddle and seat clamp are removed so you can clamp the top of the post in a large, fixed vise. Clamp the crap out of it and go to town! You have a pivot point around which to turn the frame, with lots of leverage on the head tube.

One thing to add is this: If you CANNOT break it lose through application of various penetrants, heat, cold and force, there is the option of sawing off the top of the seat post, allowing you to hacksaw down the seat post and seat tube into the wall of the seat post. Ideally, you cut through the wall of the post, stop at the steel seat tube, and now have a slit in the post that will hopefully break it free. And if not, cut another slit 180 degrees away and now you have two separate pieces that can be removed. This would be the last-case scenario step I'd take before tossing the project into the dumpster.

Good luck! Let us know how things turn out.

PS After reading the bike mechanic hack's account, I'd suggest another approach in the leverage attack. A seat post isn't that strong or effective at resisting high, localized clamping forces. In other words, a pipe wrench would quickly crush a seat post under high leverage and/or torque. It would make sense to me to press-fit a plug into the top of the seat post before applying any high clamping forces. (this assumes, of course, you don't have a nice square/flat surface to grab under the seat clamp. Some posts have a nice flat to grab with a vise. Others do not.

sweeks

How about spraying a refrigerant into the seatpost to take advantage of the differential expansion?

LV2TNDM

Plug the bottom of the seatpost and pour in liquid nitrogen while simultaneous heating of the seat tube with torches on both sides. You'd think you'd get enough differential expansion & contraction to break it free. But again, no guarantee.

Amt0571

The idea is to heat it and let it cool repeatedly hoping that the diferent expansion of both materials breaks the corrosion that holds them together.

I have a can full of DOT 5.1 brake fluid that I use to bleed my (modern) road bike brakes. Will it work like DOT 3? it seems like a good idea.

andrewclaus

It looks like DOT 3 and 5.1 are the same glycol ether composition, different boiling points, so it should work the same.

I've never tried it on a seat post, mainly because of the paint issue. I've never had luck with any penetrants (or with thermal expansion) on a stuck seat post, only with torque and impact. But DOT 3 worked on a stuck auto suspension nut the other day, when nothing else did after hours of attempts.

Amt0571

So far I've not had good luck with the seatpost. It's stuck and refusing to move. I have not tried putting penetrating oil from the bottom bracket as I've been unable to remove the cranks because my socket doesn't fit.

I'm waiting for a new socket and hoping that attacking the problem from the other side works better.

To make matters worse, I disassembled most of the bike components and found that the 3ttt Record stem has a crack around the bolt that holds the handlebar clamp. So I now need a new stem.

Fortunately, the rest of the components are OK except for some rust. I'm not positive on the BB though, but I won't know until I can remove the cranks.

Thomas15

cut to the chase

CyclingFool95 

Aluminum post and steel frame, there's always the lye option. Be careful - read up on what the risks are (to you - it's harmless to the bike).

Murray Missile 

Nothing works on aluminum like Kroil IMO.

Amt0571

I'm leaving destructive options as a last resort in case nothing else works. I'd like to save the seatpost if possible, and I'm not in a hurry to remove it. I'm already bummed that I have to find a new stem...

curbtender

I'm guessing you are trying the upside down soak? Maybe try adding some vibration to it, like an orbital sander. I've gotten them out with a guy holding the frame down and another turning with two pipe wrenches while hitting them with a hammer. You may also want to run a hanger down the seat tube to see how much post is in there. If it's pretty deep, that lye my be your only option.

Amt0571

I'm going to try the upside down options as soon as I manage to remove the cranks. The sockets I have don't fit in the cranks and I'm looking for one that does.

I also had an idea. Since there are a couple of holes in the bottom bracket, maybe I can fit something there and hit it with a hammer hoping that it pushes the seatpost out.


I'm not sure if I will be able to fit something that is rigid enough though.

3alarmer 

...which is exactly how the process works for removal. The different expansion coefficients work to break the bonds that have formed through galvanic corrosion. Thus the recommendation to go through 2 or 3 heating and cooling cycles. It doesn't matter whether the aluminum is interior to the steel surface or exterior to it. The general idea is to get them to expand nd contract at different rates.

I often puzzle over comments I see here made by people who have not actually done something in practice. It seems like a good way to go astray.