Stuck steel seatpost in Trek Aluminum Frame
03-25-21, 04:29 PM
#1
Still learning
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Stuck steel seatpost in Trek Aluminum Frame
New twist to an old problem, but the metals are reversed. Tapping doesn’t budge the post and a pipe wrench just crushes the steel post. Can’t use caustic soda, would ruin the frame. Son’t want to scorch the paint either.
Such a moron, I forgot to check before buying it.
Trek 7000
Such a moron, I forgot to check before buying it.
Trek 7000
03-25-21, 04:50 PM
#2
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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
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.
03-25-21, 05:13 PM
#3
Senior Member
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 
.
. If the chemical/penetrant methods yield “no joy”, I’d just sacrifice the seat post and get a new one .
03-25-21, 05:26 PM
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Thanks for catching that I meant to say seat post. It's just something to help the clamp hold onto and not slip.
03-25-21, 05:43 PM
#5
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. 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!
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.
03-25-21, 05:58 PM
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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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03-26-21, 12:13 AM
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That was my first thought, also. Might have to repeat a few times, though. Patience will be rewarded - hopefully.
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03-26-21, 06:10 AM
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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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03-26-21, 06:23 AM
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Patience, grasshopper.....
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.
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:
Failing patience and hot removal, one can resort to what I found to be a last-resort:
03-26-21, 12:46 PM
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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.
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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03-26-21, 02:34 PM
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And......wait some more!
I’ve 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, I’ll follow dddd’s recommendation and pour myself a small one tonight and wait with you!
I’ve 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, I’ll follow dddd’s recommendation and pour myself a small one tonight and wait with you!
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03-26-21, 04:22 PM
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And......wait some more!
I’ve 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, I’ll follow dddd’s recommendation and pour myself a small one tonight and wait with you!
I’ve 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, I’ll follow dddd’s recommendation and pour myself a small one tonight and wait with you!
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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03-26-21, 06:17 PM
#21
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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.
03-27-21, 09:41 AM
#22
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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 Triplecrank92’s method. PB Blaster through the bottom bracket. I kept spraying for a few days and every night I’d 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.
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
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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03-28-21, 08:07 PM
#24
Recovering Bikeaholic
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!!!!😆
03-29-21, 01:40 PM
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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
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