Aluminum seatpost broken into a steel frame

Question

Similar to Aluminum seatpost stuck to a steel frame but worse, since the seatpost is broken exactly at the end of the seat tube. Image below.

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Below is a suggested fix using a quill stem as a "puller"

My seatpost is very old and thick so that the 22mm stem won't fit (I have a 1,6-1,8 cm inner diameter, the broken seatpost length is about 6-7 cm).

Any idea ??

Answer 1

I have removed a shoved-in seatpost using a length of threaded bar, and some washers and nuts. I inserted a washer and two nuts (the second as a locknut) via the bottom bracket shell, threaded the bar into those, and on the top side added a washer bearing on something (I can't remember the details but I think some wooden blocks onto the frame sufficed); screwing a nut onto the exposed bar pulled the seatpost out.

Obviously this relies on the seat tube/seatpost being a good match for a common washer size; I think mine was a good match to M12. Getting the bottom nut/washer to engage was also rather difficult, complicated by parts of the lugs intruding. My seatpost may also not have been particularly stuck.

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(Note from OP) This one is my accepted answer because was the one of my choice and kind of less expensive too, spent 1,5 euro on a 1m threaded bar and some M8 nuts and 8mm washers. Inserted the bar with the washer side inside the seat tube and with some firm and strong pulling in such a way that the washer was grabbing the seatpost bottom (like simulating an reverse hammer use). Had to work for 15 minutes but after 5 minutes I got the seatpost already exposed by 3 centimeters, maybe my one was not particularly stuck.

Answer 2

That's a challenge right there - I hope the bike wasn't being ridden at the time it failed !

Clearly the post is dead, so damage to that is okay. You want to save the frame.

1. Remove the seatpost pinch bolt. I see its loose, remove it to expose the slot. Remove the rear wheel and anything else like mudguards/fenders or rear rack that in the way. Maybe even remove the rear rim brake caliper.
2. Use a dremel or a thin-bladed cutoff wheel in a grinder to cut vertically through the seatpost slot, making a relief slot. Avoid cutting the frame as much as possible. Leave 5-10mm of uncut seatpost visible at the bottom of the slot.
3. This cutting will generate heat and aluminium dust. It may ignite penetrating oil or scorch paint. Use care.
4. Use a punch at the top of the post to slightly close the seatpost slot, effectively making the top 20mm slightly conical and pulling it away from the steel frame.
5. Use a drill to make a small divot in the seatpost at the bottom of the slot, where you left the uncut metal. Don't drill a hole - you're making a seat for a punch.
6. Use a hammer and punch/blunted nail into this divot to drive the seatpost upward. If you get movement but it stops and binds, you may need to extend the cut slot and reset your position.

Once there's an inch or so of seatpost exposed, then you can get vise grips or a plumber's spanner or a bench vise onto the stub and have a better grip.

Once its clear, you'll want to touch up the paint as there will be chips and damage. It may be worth considering a different material for your replacement seatpost for peace of mind too.

Answer 3

I can imagine two approaches.

1. Use an internal bearing extractor. This is a split cylinder that can expand to clamp against the inside wall of the seatpost, much like a quill stem clamps against the inside of the steerer tube.
2. Use a screw extractor. This is basically a big, aggressive screw that will cut its way into the seatpost.

In either instance, I'd liberally drip liquid wrench all around the seatpost to loosen it up, so that once you've got purchase on the seatpost, it comes out more easily. This assumes it's not permanently seized.

Also, you'll probably want to remove the bottom bracket before dripping liquid wrench into it.

Answer 4

I had a similar snapped seatpost on my MTB recently. The seatpost also broke off near the clamping point. After visiting various forums, I opted for an approach that I have not found anywhere.

My seatpost was aluminum; external diameter 27.2 mm, internal 21.2 mm. The bike frame is made of titanium (Airborne). My approach was to hammer a star nut, like you use in an Ahead steer tube clamp, into the remainder of the post. That requires several strong hammer blows. To prevent the post from sinking deeper into the tube, due to those blows, I first drilled a hole in the post from the side, through the open slot in the collar of the seat tube. A nail or screw in the hole will prevent the post from sinking any deeper (photo 1).

Then I placed a 1 cm high shim (28.5 mm internal) on top of the seat tube(31.7 mm external diameter), and on top of that a strong cap with an extra long screw (40 mm). I greased the screw well to ensure that it turns with little friction through the thread of the star nut at high tensile forces. The most exciting moment was of course when tightening, whether there would be movement in the pen. I had to tighten the Allen key quite a bit but then I saw the hole move up. Gradually, the hoisting movement became smoother and smoother. Each time the pen reached the height of the shim, I placed a new shim on top of the previous one. After hoisting about 6 cm I had enough grip to lash up the remainder with a pair of water pump pliers.

The pictures make the story clearer. Photos 1 and 2 were taken when the pen had already risen about 1 centimeter ; the hole to the side was at the bottom of the slot at the beginning of the operation. The last photo shows the entire set of tools and the two halves of the seat post.

The setup enables to exert a high pulling force on the pen. An Allen key with 10 cm length and a metric screw treaded with 1mm/turn results in a force amplification by a factor 600!

Note : star nuts are available in a range of diameters : 18 -23 - 26 - 29 mm.

Answer 5

There's no pleasant option here but I think in lieu of very specialized tools (like a slide hammer collet that could grab it securely enough), you're limited to cutting it out.

Use a hacksaw blade clamped in vise grips and go slow.

Control the process by taking advantage of the difference in hardness between the steel frame and the aluminum post. Select a basic blade, not something super hard that you would choose to cut steel with on purpose. So avoid carbide for example. You won't hurt anything if you kiss the teeth up against the steel once you're through, but you don't want to go more than that.

Carefully put in a couple slits and you should be able to get it worked loose.

Answer 6

I don't have any tested complete solution, but here are a couple of thoughts:

1. Are you able to file a little slot in each side where the frame dips down and exposes the seatpost a bit? If so, you could then slot a long narrow piece of metal across it, maybe even the file itself, and use it like a giant flat end screwdriver to rotate (wiggle) it back and forth after applying some WD-40. Just gently wiggling it back and forth while the WD works its way in might loosen it enough to them pull it out with some needle nose vice grips or something.

Rough sketch of what I'm talking about:

2. A cross-section of the seat post and set tube across the bike would look roughly like below (blue = seat tube/ frame, grey = seat post). Is there any L=shape kind of rod or tool you could poke down past the bottom, and then pull up on the bottom of the seat post? E.g. like the green lines. You mentioned the post is stuck pretty good right now, so counter-intuitively, putting some WD on the top interface between the post and frame, and very gently tapping down on the post with a hammer might loose it enough that you could then pull it back up with this method.

3. This would be more involved, but some frames have small drain holes in the bottom side of the bottom bracket. If so, then a cross section along the bike frame would look something like this below, and I'm wondering could you find a thin rod that's still stiff enough to put up through one of those hole and tap on the bottom side of the seat post as shown below.

Personally I feel like the first option would be easiest and have the greatest likelyhood of success. I suspect the post wants some torque applied to it first to loosen it up.

Answer 7

It's possible that the post and the frame have undergone galvanic corrosion, meaning that the aluminum and the steel have chemically fused. This will make mechanical removal much more difficult and virtually impossible to do without damaging the frame.

In this case you can use a lye (sodium hydroxide) solution, to melt the aluminum. Lye can be found at stores that sell soap making supplies.

I had to do this once with an old 80s road bike. What I did was cut the seat post to the point where it looks like what you've got. Then I removed the bottom bracket and stuffed a bunch of cloth and plastic into the frame up the seat tube to plug it from the bottom.

Then I used a funnel on the top to gently pour lye solution (water and lye) into and onto the broken seat post. This slow melts the aluminum but leaves the steel in tact.

This process takes some time and patience and a bit of trial and error to find a way to keep the lye around the seat post and not have it leak out too quickly. I managed to do my bike in a few hours with a small jars worth of lye.

WARNING: Lye solution is incredibly caustic on skin and will give you chemical burns if you come in contact, even worse in the eyes, etc. So you need to wear rubber gloves and safety goggles if you want to be safe. You'll also want to avoid it coming into contact with any other aluminum components on the bike. Best to strip it down.

EDIT: A note from commenter:

Another health warning that you should note with this answer is that you'll generate H₂ gas as a byproduct – which is explosive. I imagine you don't smoke while doing bike work, but I'd personally let the reaction run to completion and then start the metalwork, rather than risking a bubble of gas e.g. collected inside the frame suddenly meeting a spark and causing mishap...

On that note, only do this outside or in a very well ventilated area.

Answer 8

Use a bolt that fits inside the seatpost

Aluminum is quite soft, so a steel bolt of suitable diameter will thread into it. You can help getting it started by filing the first few threads of the bolt a bit thinner and the edge of the seatpost to a taper.

Use a wrench to screw the bolt as far into the seatpost as it will go. After that, the tube should start spinning and hopefully the spinning action will break it loose and you can pull it out.

Note that this will not work if there is already a relief cut in the seatpost, as the bolt would then expand the tube and make it even more tight.

Answer 9

I use PB B'laster Penetrant for stuck items. Also might try heating everything up as hot as you can without stripping the paint. Heat will help break the adhesion layer between to two metals. Then use one of the techniques listed.

Answer 10

The simplest thing I would try first is just to find a pair of pliers small enough to fit in the pipe, force them open to try and "grab" the inside of the pipe, then twist/pull to see if it comes out.

If it's really stubborn and you need more grip, you can try getting a "rubber expansion plug" or "shaw plug" that's the right size to fit most of the way into the hole. As an example, here's one for pool pipes:

When the nut is twisted, it applies pressure that forces the rubber to expand out and will give you extremely good grip on the inside of the pipe. Then you just pull on this instead. Just avoid ones that use plastic nuts/bolts.

Edit

Here's another style:

Answer 11

I've already replied with three different options for handling this issue. But some of the other answers and comments have inspired another idea on how to handle this. I'm curious to hear what others think of this option. It's a bit involved so I'm posting it separately.

User jpa suggests threading a bolt down into the broken off seatpost then using that to pull it out. Criggie points out in a comment that the self-threading of the bolt may give way (strip) before breaking whatever bond exists between the broken off seat post and tube. And elsewhere, Christopher Reid points out that galvanic corrosion may have chemically bonded the seatpost to some degree inside the seat tube.

So there are two challenges: break whatever bond exists between the seatpost beyond the normal friction bond that would keep a seatpost from sliding from pure gravity; and also get the seat post out of the seat tube.

My suggestion is a modification of jpa's bolt-as-extractor with some additional details to handle breaking the bond, assuming it can be broken mechanically as opposed to chemically.

1. Starting off, you've got a seat post (orange lines) stuck inside a seat tube (blue lines) like this cross-section:

2. Next, as suggested by jpa, you want to find a bolt that you don't mind destroying. I think you want a particular bolt whose shank diameter (smooth part of bolt) and minor diameter (measured between valleys of threads) is a little less than the inside diameter of the stuck seat post, and whose major diameter (measured between peaks of threads) is a little more than the inside diameter of the stuck seat post. This should allow you to thread the bolt down into the inside of the seat post. Filing the edges of the leading face of the bolt and seat post may help this. Try threading the bolt down into the seat post. If you can't get it start threading at all, abandon this method. If you can, try to estimate how much you'll be able to thread it down, and cut off the remainder of the threaded portion of the bolt. I think you probably want 1/2" to 1" threaded in, with no thread left exposed. After this step you hopefully have something like this:

If the seat post happens to start turning from the force of threading the bolt in alone, then continue applying torque to the bolt while pulling up on it with vice grips or something, and you're done. Assuming you're not that lucky...

3. Now cut the head off the bolt leaving only shank exposed:

4. Next, find another piece of tubing ideally the exact same size as the seat post, so it will slide over the bolt shank, but inside the seat tube. Depending on how much snapped off seat post was left attached to your seat, and what condition it's in, cutting the damaged end off of that might be just right. This new piece of tubing is shown in purple here:

5. Next, we'll hopefully break whatever bond is holding the seatpost in place (hopefully just a high level of friction or minor corrosion bonding). Apply a Liquid Wrench type product and gently tap on the top of this tube with a hammer so that the force is conveyed to the top of the stuck seat tube. Make sure to impact straight down so as not to dislodge the bolt, to encourage the liquid wrench to work its way down any gaps between seat post and tube. Keep a close eye on the seat post and if you see it move at all, stop and try pulling it with some vice grips on the bolt.

6. If gentle tapping and liquid wrench doesn't get the post moving, try slowly increasing hammering intensity until the post starts moving. Hopefully this will be enough to break anything short of a very thorough corrosion bond between the post and tube. Once the post starts moving, stop hammering and pull it out with vice grips. Don't start off wailing on it with the hammer because if you apply way more force that just what's required to break the bond, you might just push it way further down, making it hard to retrieve.

Caveats:

1. Hammering might loosen the bolt threading. That's why I'd recommend getting it threaded in at least 1/2". Not just one or two threads.
2. If there is a wide spread galvanic corrosion type bond, continuing this method until it breaks may do damage to the inside of the seat tube. Use your common sense in determining when to stop hammering and give up on this method. You can always retract the bolt with vice grips and try another method.
3. If you start off hammering really hard and the bond is minimal, I could imagine a scenario where the seat post dislodges and goes wizzing down the seat tube and damages something else down there, e.g. the bottom bracket. So ramp up the hammering from a very mild initial impact and watch carefully for post movement.

Answer 12

Another option is to talk to someone with a milling machine, or a big drill press/pillar drill. Do NOT try this with a hand drill

If you treat this as a bolt broken off in a hole, then the process is similar.

You'd start by fixturing the bike frame under the drill/mill spindle such that the seat tube is vertical and centered. Then you have to secure the frame against moving or spinning. This step often takes longer than the drilling

If the hole in the tube is 16mm then start with a 16mm demming twist bit and it should align well with the hole. Adjust if required. Use plenty of WD40 or a specific aluminium-cutting lubricant to protect the drill.

Then step up through 18mm, 20mm, and maybe 21mm. Either the force of the drill will overcome the corrosion and the post will move on the drill, or you'll bore out enough of the wall thickness so what's left will invert itself by poking a thin screwdriver down the sides between frame and remaining seatpost. There is a risk the stub of seatpost falls down inside the frame, which is to be avoided.

Ideally you want to avoid cutting any of the steel from the frame, but a light touch won't make any real difference. The frame will be narrowest in the top 100mm, and will be slightly wider internal diameter below that point.

When installing a new seat post, clean remaining corrosion from the bore with a wiffle stick or a light cylinder hone. Use grease or an assembly lube to keep the steel off the aluminium seatpost, or fit another metal. Anodised aluminium seat posts may be perfect for this task.

Answer 13

This article has some ideas that have and haven't been listed here. The freezing idea sounds very doable.

https://turncranks.com/aluminum-seatpost-stuck-in-steel-frame/