When I first came to own my Team Mongoose 25 years ago, I could barely touch the pedals while I was sitting on the seat. The first thing I tried to do was get the seat post out. I wiggled it, sprayed WD-40 and let that soak in, but it did nothing! 25 years on and the post was still stuck in there!
Back in the day, my mate told me his dad drilled his seat post out of his Mongoose because it was stuck. I was thinking that I was just a weak kid so I'd give it another crack. I thought with the internet on my side this time I was sure to find an answer.
The first thing I tried was some ammonia. I read a few blogs and forums saying that pouring ammonia in there and letting it settle over a few days loosened up all the crud and the post would come out with a little force. I left it in there for a week. The photo above shows the ammonia sitting in the seat post tube. A week went by and it did nothing!
A good mate of mine told me he got his stuck seat post out by soaking WD-40 in the post and between each crevice for 30 minutes, then sticking that into a vice tightly, so tight that you squashed the post. Then, using the frame as leverage, spin the post from side-to-side and you would hear a grind and it would be free. So, 30 minutes soaking with WD-40 and straight in the vice, tightened it up until the seat post was almost flat, started to turn and it completely snapped off! That trick was busted.
I decided to make a shim out of a hack saw blade and try to cut it out. I wanted to find out how far the seat post was jammed in before I started trying to cut it out. I grabbed a old coat hanger, bent one end and pushed it down until it was caught on the end of the post.
I chopped off most of the seat post and left about two inches to have something to grip onto when I squashed the post out of there.
I jimmied up a handle to the hacksaw blade using gaffer tape and went to cutting. About 3 hours in I was finally getting through the post, but only at the top.
I stuck the end of a post into a vice and begun using the frame as leverage to try to spin the post free. After a quarter of a turn I heard a crack and the top of the aluminium post snapped into pieces, but the rest was stuck inside. I had nothing left of the post to grip onto and I thought that the only thing left was to pay someone to drill the seat post out. Well, that's what I thought before I jumped onto YouTube!
I stumbled on a few videos that discussed using caustic soda to dissolve the post out of the tube. The chemistry behind this was that caustic soda has a chemical reaction that dissolves the aluminium and creates hydrogen gas, but it doesn't dissolve steal, what the Mongoose frame was made of. If you fill the seat post tube with caustic soda, the aluminium dissolves and you're left with a clean seat post tube.
I covered the bike frame in glad wrap and gaffer tape. I gaffer taped a plastic cup to the top of the seat post and tried to fill all the holes. I mixed half a tub of caustic soda into some warm water. I read somewhere that warm water helped speed the reaction, but to be careful because warm water went very volatile when you add caustic soda to it. I then poured the caustic soda solution into the cup, filling it almost to the top.
Instantly the water turned white, then brown and started bubbling. A white gas, the hydrogen gas, could be seen coming out of the brew. It hissed and spat all over the place! But, 45 minutes later, the seat post couldn't be seen any more. I let it sit for another hour, then poured what was left into a plastic container. Out came a lot of dirt, crud, rust and small shards of aluminium!
I rinsed the post tube out thoroughly with water and begun scraping the inside with a metal rod. It was completely clean and free of any of the aluminium seat post! This actually worked and it was amazing to watch!
My first big success! I've vowed never to use an aluminium fluted seat post in a bike again!
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