The quick (and fun) way to free a stuck seatpost...

tango_down Posts: 87
edited February 2013 in Workshop
My tale of woe and redemption begins with several days of pulling, twisting, swearing, sawing, hammering and generally abusing my seatpost. It was stuck. I tried filling the seat tube with vinegar, I tried litres of WD-40, I tried voodoo. Nothing.

Enter our hero, caustic soda (sodium hydroxide). After days of hard work, a £1.70 bottle of white powder did the job for me in about two hours. Note that this will only work for an aluminium post in a steel frame.

Saw the seat post off, leaving about an inch above the clamp. Remove the bottom bracket and anything else aluminium from the bike. Seal up the bottom of the seat tube with a big wad of blu-tac and seal the bottle holder holes too. Test it with water to make sure everything's properly water-tight.

Mix up some caustic soda with water. Go for half and half by volume (this is seriously bloody strong, WEAR EYE PROTECTION and rubber gloves). Do it in small volumes: say 200ml of water to about the same amount of CS. The best receptacle is a plastic measuring jug (it'll ruin a glass one).

Work outside. This is going to be messy. Dribble your solution over the seat post and watch in awe as it begins to bubble and steam, and your bike turns into a miniature volcano.

You'll treat the caustic soda with more respect after seeing this bit.

Keep at it. Fill the tube with CS; it'll bubble up and come out, so you need to keep topping it up. I'd already hacked at the seat post extensively, so it had lots of cuts in it. I think these helped provide more surface area for the CS to attack.

With the CS at this (fairly insane) concentration, the whole process doesn't take long. Your seat post will submit pretty rapidly. The photo shows what happened after two hours of this treatment.

Once you've had your fantastic moment of victory, turn the hose on your bike. Wash it down with loads and loads of water to make sure the CS is well diluted. Rinse out the seat tube repeatedly. Try to think of a responsible way to dispose of all the black aluminium hydrate solution that's spilled out.

Go to the Classified --> Road Parts forum, buy a new seat post, and you're all set.

This was a hugely entertaining way to spend my Saturday afternoon.