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Stuck steel seatpost in Trek Aluminum Frame

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Stuck steel seatpost in Trek Aluminum Frame

Old 03-25-21, 04:29 PM
  #1  
oddjob2
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Stuck steel seatpost in Trek Aluminum Frame

New twist to an old problem, but the metals are reversed. Tapping doesnít budge the post and a pipe wrench just crushes the steel post. Canít use caustic soda, would ruin the frame. Sonít want to scorch the paint either.

Such a moron, I forgot to check before buying it.


Trek 7000
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Old 03-25-21, 04:50 PM
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What tools are at your disposal? A old Mechanic trick is to mix ATF and Acetone. Shake it up and spray it on then let it sit. Adding a bit of heat can make it penetrate better.

There's a few different methods. My fave is drilling a hole in the top of the seat post and putting a bolt inside. I then put it in a bench vice and try to twist the entire frame. If that is going no where you can use a air hammer to to hammer on the bolt and see if you can get it to budge.

Last ditch is cutting it out with a sawsall.

Good luck OP

Last edited by cbrstar; 03-25-21 at 05:22 PM.
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Old 03-25-21, 05:13 PM
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Not so sure about drilling a hole in the top of the seat tube . If the chemical/penetrant methods yield “no joy”, I’d just sacrifice the seat post and get a new one .
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Old 03-25-21, 05:26 PM
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Originally Posted by sovende View Post
Not so sure about drilling a hole in the top of the seat tube . If the chemical/penetrant methods yield ďno joyĒ, Iíd just sacrifice the seat post and get a new one .
Thanks for catching that I meant to say seat post. It's just something to help the clamp hold onto and not slip.
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Old 03-25-21, 05:43 PM
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Originally Posted by cbrstar View Post
Thanks for catching that I meant to say seat post. It's just something to help the clamp hold onto and not slip.
Was thinking that's what you meant . Even with a solid grip on the stuck seat post, I'd worry a bit about too much leverage perhaps causing some damage to the frame. I'd definitely stop short of "going medieval" and quickly move to sacrificing that seat post!
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Old 03-25-21, 05:45 PM
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Your only real choice would be an auto body shop. They would heat up the seat tube with a blow torch and then rip it out. But aluminum and steel expands at different rates so you may be in a bit of a pickle. You might also bend the frame when ripping the seatpost out. If you wanna risk it, go to the body shop. If not, ride the way it is and maybe try a different seat.
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Old 03-25-21, 05:58 PM
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Originally Posted by Moisture View Post
Your only real choice would be an auto body shop.
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Old 03-25-21, 06:46 PM
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Why the heck did someone use a steel seatpost on this aluminum bike. Was it meant to be a cruel joke for the next owner??
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Old 03-25-21, 09:27 PM
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The steel will expand less and more slowly than the aluminum. I'd go for a hair dryer on the frame and Liquid Wrench - they've worked wonders for me many times.
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Old 03-26-21, 12:13 AM
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Originally Posted by Steel Charlie View Post
The steel will expand less and more slowly than the aluminum. I'd go for a hair dryer on the frame and Liquid Wrench - they've worked wonders for me many times.
That was my first thought, also. Might have to repeat a few times, though. Patience will be rewarded - hopefully.
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Old 03-26-21, 12:52 AM
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Try to spray with wd40 and let it there for a couple of days.It is thin and maybe will do the job.
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Old 03-26-21, 06:10 AM
  #12  
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Originally Posted by coolmind View Post
Try to spray with wd40 and let it there for a couple of days.It is thin and maybe will do the job.
Or PB Blaster and same approach. Turn it upside down, remove BB and fill up the seattube with a lot PB Blaster and.......wait!

Last edited by Triplecrank92; 03-27-21 at 11:42 AM.
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Old 03-26-21, 06:23 AM
  #13  
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Originally Posted by Triplecrank92 View Post
Or PB Blaster and same approach. Turn it upside down, remove BB and fill up the downtube with a lot PB Blaster and.......wait!
And the key word there is "wait". It does you no good to spray a penetrant oil on a part and immediately start wrenching on it. It takes time, and often multiple applications of the penetrant, to work. Overnight is good, or, if it's really stuck, a couple of days, adding penetrant each day.
Patience, grasshopper.....
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Old 03-26-21, 06:32 AM
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A little tappy tappy with a hammer can help the PB creep in some... while waiting of course.
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Old 03-26-21, 07:53 AM
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Big rubber hammer or a piece of wood on the seat post and then tappy tappy hammer.
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Old 03-26-21, 08:44 AM
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Aluminum has a higher expansion ratio than steel, so heating from the outside should make the frame expand more than the post. If there is any galvanic corrosion, a penetrant and maybe a slide hammer, will be needed to break the bond. All bets are off if they forced an oversized post into the frame.
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Old 03-26-21, 12:38 PM
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Always happy to share a rare "wrenching" victory, as in this case where an over-sized steel seatpost had been pounded in back in the ~1960's.

Failing patience and hot removal, one can resort to what I found to be a last-resort:



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Old 03-26-21, 12:46 PM
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Originally Posted by dddd View Post
, one can resort to what I found to be a last-resort:
OK, I understand what the whiskey is for -- oh, wait, please tell me you didn't pour it down the seat tube!

Again, I'll share what worked for me, but in the reverse with steel frame and alloy post (so YMMV): I was able to stick the frame and post in a chest freezer for, I don't know, a couple of days, to contract all the metal. Then, pulled it out, quickly stuck post in a vise and applied heat to down tube, all while pulling on frame for all it's worth, hoping that "differential expansion" would work in my favor. Got out a post that I had hammered in there back in 1974 when I did not know better. OP's frame looks small enough to fit in some chest freezers; mine was 60cm and almost did not fit.
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Old 03-26-21, 02:34 PM
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And......wait some more!

Iíve done the same as the others & occasionally pulled, twisted, and heated the seat tube & post to help the oil seep further into the offending corroded joint while waiting (up to a week one time).

And, just to help you out with this task, Iíll follow ddddís recommendation and pour myself a small one tonight and wait with you!
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Old 03-26-21, 04:22 PM
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Originally Posted by Triplecrank92 View Post
And......wait some more!

Iíve done the same as the others & occasionally pulled, twisted, and heated the seat tube & post to help the oil seep further into the offending corroded joint while waiting (up to a week one time).

And, just to help you out with this task, Iíll follow ddddís recommendation and pour myself a small one tonight and wait with you!
I didn't realize my Friday night drinks would be so much assistance, happy to help!

But, yeah, only thing I can add is that I've seen folks pull the bottom bracket so that they can pour penetrating oil/ATF Acetone mix/whiskey down the seat tube to reach the bottom of the seatpost as well. Pour your poison on the top of the seatpost, let soak, flip around and pour in the seatpost, let soak, repeat. Intermix some brute force on the seatpost and heat gun (careful not to scorch the paint if you can help it) on the frame in between alternating penetrant applications.
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Old 03-26-21, 06:17 PM
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Your seatpost has the cheap clamp on top but for nicer seatposts with integrated clamps I've had good success taking the clamp hardware off and putting the little head in a sewer grate and twisting.
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Old 03-27-21, 09:41 AM
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I had to do this when I also bought a bike and forgot to check the seatpost. I had success using Triplecrank92ís method. PB Blaster through the bottom bracket. I kept spraying for a few days and every night Iíd hammer on the seatpost pretty hard in hopes of getting the lubricant in there. It took a few days, but it worked. Need to be patient.
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Old 03-27-21, 11:39 AM
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If the seat post is not ovalized from the wrenching.....invert the frame as others have suggested, apply a generous amount of PB and wait for it to do its job.
Then instead of trying to "pull/twist" it out using a dead-blow hammer tap it "down" to break the seal...it should move just a little and then more PB...then twist away.
It may seem to be counterintuitive but this has worked for me many times...similar to tightening a stuck bolt a tad to break the corrosion before removal.
GL, Ben
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Old 03-28-21, 08:07 PM
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Originally Posted by Triplecrank92 View Post
Or PB Blaster and same approach. Turn it upside down, remove BB and fill up the seattube with a lot PB Blaster and.......wait!
Happened to me a few years back.... PB Blaster, patience and a bench vise... Had my bike clamped in upside down, then pulled and pushed the frame (twisted) back and forth with all my might... Thought I was going to break the frame... It finally broke free!!! Whew!!! Lesson learned; grease that post!!!!😆
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Old 03-29-21, 01:40 PM
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Originally Posted by xiaoman1 View Post
If the seat post is not ovalized from the wrenching.....invert the frame as others have suggested, apply a generous amount of PB and wait for it to do its job.
Then instead of trying to "pull/twist" it out using a dead-blow hammer tap it "down" to break the seal...it should move just a little and then more PB...then twist away.
It may seem to be counterintuitive but this has worked for me many times...similar to tightening a stuck bolt a tad to break the corrosion before removal.
GL, Ben
I like Ben's method, but I would drill a hole in the seat post and insert a bolt just in case the thing broke free and dropped too low to retrieve.
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