stuck bike seat post

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  #1  
Old 05-10-09, 08:53 PM
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stuck bike seat post

I acquired an old Peugeot mountain bike that had sat out in the wet weather for a long time. I lubed the various mechanisms and did a little repair and adjusting and got it working pretty good. Problem now is that I can't move the seat post up, it's stuck hard. I tried strong penetrating oil (PB blaster), let it soak, still doesn't budge. Tried twisting with a pair of channel locks, still won't budge.

I was considering heating the frame with a propane torch and then trying to move the post, but I was reading somewhere that if the post or the frame is aluminum, the heat just makes it worse. I'm not sure whether the frame or the post is aluminum, would anybody have an educated guess?

Also, apparently if the frame or the post is aluminum, apparently ammonia is supposed to break the bond somehow, and I haven't tried that yet either.

Anybody have more suggestions or perhaps a sure-fire method that should get the thing unstuck without damaging anything?
 
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Old 05-11-09, 04:06 AM
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A magnet will tell you if it is AL or steel. A little heat will help as it will expand and contract. Doing that many times will weaken the bond. If the seat post is hollow you can drizzle a bit of oil inside and then flip the bike so that oil starts to soak in around the post from below. Tap it down a bit to loosen it up. create a slide hammer or clamp something onto it where you can use a hammer to drive it out. Can of freon to cool the post while you heat the frame. Again, never too hot.

Bud
 
  #3  
Old 05-12-09, 08:32 AM
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Originally Posted by Bud9051 View Post
A magnet will tell you if it is AL or steel. A little heat will help as it will expand and contract. Doing that many times will weaken the bond. If the seat post is hollow you can drizzle a bit of oil inside and then flip the bike so that oil starts to soak in around the post from below. Tap it down a bit to loosen it up. create a slide hammer or clamp something onto it where you can use a hammer to drive it out. Can of freon to cool the post while you heat the frame. Again, never too hot.
With the magnet I was able to discover the seat post was aluminum, and frame is steel. I finally got the post out, but it was a tremendous struggle as it was stuck solid in the tube. Penetrating oil didn't seem to help, as it's good for steel on steel but not for AL on steel. I heated then cooled the tube several times with propane torch but I don't really think that helped too much either, maybe even made the aluminum post inside expand more. I was lucky to finally get it to budge at all. I lifted the bike into a bench vise and clamped the vise onto the post and twisted and tugged and pulled from every way I could with every ounce of strength I had. Eventually the post broke off. I ended up having to sawzall the inside remnant of the post into slits and then pull out the chunks with locking pliers. The seat post was longer than I had assumed, and was down stuck in the post quite a ways.
When I buy an new seat post and install it, what's a proper lubricant/grease or other substance I should use on the inside of the seat tube or the outside of the post to prevent it from sticking like this again? Regular old axle grease? Anti-sieze compound? Something else?
 
  #4  
Old 05-12-09, 10:21 AM
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We never did anything special other than a light spray lubricant.

My guess would be we were more worried about getting the seat post to stay put rather than not corroding in place.

Bud
 
  #5  
Old 05-12-09, 10:26 AM
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Yep....just a light spray type....
You should pull it out once in a while, like when you lube the chain and cables.
 
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Old 05-12-09, 11:22 AM
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Thanks for the update. I'm just glad you have the resourcefullness to figure out someway to make it work. Those types of projects can be really annoying. Something that sounds simple and should take 5 minutes ends up eating several hours of your day.
 
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Old 05-12-09, 12:37 PM
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Originally Posted by Bud9051 View Post
We never did anything special other than a light spray lubricant. My guess would be we were more worried about getting the seat post to stay put rather than not corroding in place.
Yeah, but if the clamp is holding like it should, shouldn't that prevent the post from slipping down, even if the post was super greased?
 
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Old 05-12-09, 12:42 PM
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Originally Posted by Pilot Dane View Post
Those types of projects can be really annoying. Something that sounds simple and should take 5 minutes ends up eating several hours of your day.
Yes exactly that project was one royal pain in the a.. ! Messed with it for four hours. I thought at first it'd probably come right up if I squirted a little penetrating oil on it. But no. No way.
 
  #9  
Old 05-12-09, 01:19 PM
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Aluminum posts always held better than steel, but the final assembly test was to clobber the nose of the seat sideways quite hard to make sure the seat clamp and post were tight. You can lube it if you are nervous. If it won't tighten properly, (don't kill it) just clean off the grease and start over. At least it will come out this time.

Bud
PS when things go wrong like this it is called turning a project into a career and I have had many careers.
 
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