Wednesday 14 October 2015

Removing an Aluminum Seatpost From a Steel Framed Bicycle: The Hardest DIY Repair You Will Ever Do!

This is a bike repair situation that you will hopefully never find yourself in...removing an aluminum or alloy seatpost from an old steel framed bicycle.  The steel and aluminum form a chemical bond over time (that cannot be loosened with penetrating oil), which makes the removal or adjustment of the seatpost nearly impossible.  Somehow, I have found myself in this situation twice, and both times I have needed to put in a huge amount of effort to remove the post.  Mostly as a result of my pure determination, I am 2/2 for getting these posts out, so I wanted to share what I found to be effective, and what was a waste of time.  I'll start with the least extreme approaches first (which in some cases may be enough) and finish with the most extreme (when there is no hope left, you try this).

Start With These: Not Extreme Approaches

Twisting With the Seat

The simplest approach is just to loosen the seat post binder bolt, and then twist the post using the seat.  You will likely have to twist very hard, so temporarily installing an older seat is advisable.  Don't be surprised if the post doesn't move.
Use a screwdriver to open the seatpost collar more

Using a Vice  

To get more leverage, you can put the top of the post in a vice.  This will give you a lot more leverage on the post, and can be very effective.  Unfortunately in my experience, the top of the post has just separated from the tube section of the post, making twisting impossible.

Using a Pipe Wrench

At this point, it becomes very difficult to salvage the old post.  Using a pipe wrench directly on the tube section of the post will give you a lot of leverage, but it will likely wreck the post.  This will be the last thing you can try to remove the post before having to move on the more extreme measures.  Hopefully for you, it a successful removal with this method HERE  

When All Else Has Failed: The Most Extreme Approaches

Hacksaw Blade Trick

In both of my aluminum seatpost removal experiences, I have needed to use this approach.  Once you have decided to pursue this method of removal, there is no going're all in.  
The first thing you need to do is cut the post horizontally (about an inch from the top of the seat tube) to allow you access into the hollow opening of the seatpost.

At this point, you now need to start cutting vertical groves in the seatpost.  The aim is to make 2 vertical cuts 90 degrees apart down the length of the post.  A few notes on this approach.  Making the vertical cuts takes a lot of time and patience.  You need a good hacksaw blade and you need to make sure you cut all the way through the post.

It should look like this

Once these cuts are complete, you should then be able to remove a quarter section of the post (I usually try hitting it with a screwdriver to break it free).  Pliers or vice grips can then be used to first squeeze (crush), and then remove the remaining three quarters of the post.

This approach worked for me in my first seatpost removal, but proved ineffective in my second (the post was really long and the blade couldn't reach the bottom).   I then had to move to the most extreme method of removal..chemically dissolving the post.

Chemically Dissolving the Post (Using LYE)

This really is the last resort.  If this doesn't work for you, then your post is never coming out.
Start by removing as many (if not all) of the components from the frame, and put protective covering on the paint (unless you are planning on re-painting too).  You then need to put some kind of a plug at the bottom of the seat tube so the chemical will not just run out the bottom bracket.

So, to start things off, you first need to get yourself some 100% lye crystals.  Most stores don't carry them, and online purchasing can be tricky, but I was able to locate them at Home Hardware (Link to product here).

Be very careful with this stuff

The way this works is that the lye will dissolve the aluminum (the seatpost), but will not damage the steel (the frame).  

So here is where it gets a bit dangerous.  Lye is very toxic stuff, and the chemical reaction it makes is also very toxic.  It is recommended that you wear chemical proof gloves and a respirator at all times.  If any gets on your skin, go rinse it off right away.

To start the process, dissolve some of the lye crystals in water (maybe around 2:1 water to crystals ratio).  You are now ready to start dissolving the post.  

Carefully fill the seat tube with the lye and water solution (if sealed well, it will fill quite fast).  As soon as the solution hits the aluminum, it should start making a hissing noise.  Soon after, white gas (actually Hydrogen gas) will start coming out of the tube.  The liquid inside the tube will probably start bubbling soon after.

Now, you just need to let the lye do its work.  The post will start bubbling and hissing quite violently, and you will see the aluminum bubbling out as a grey goo.  Let the post bubble away for maybe 30-60 minutes and then go back and top up the tube with fresh lye/water.

After a couple hours of this, the post should be ready to remove.  I literally took a pair of pliers and pulled it out like a tissue out of the was that easy.
Right is before, left is after
So, there ends my adventure for removing this seatpost.  As I said at the beginning of this seatpost (oh wait blog post), hopefully you never actually have to do this....but if you do, I'm hoping this was of help.


  1. Thanks for sharing the seatpost repairing story. I am also looking to upgrade my bike hope it will help me a lot in repairing seatpost.

  2. This can be really a hassle, especially when the steel frame is fully rusted out