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Seat / seat post sagging

Old 03-07-18, 10:56 AM
  #1  
imobilinpedalus
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Seat / seat post sagging

Alright, i`ll admit it, i`m a bit on the heavy side. I am also growing tired of having to reposition the seat every now and then after it seems to slowly sag while out riding. The clamp is a quick release type but no matter how hard i tighten it it always seem to develop a sag. Is the solution i`m looking for as easy as getting a fixed bolt type clamp?
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Old 03-07-18, 11:25 AM
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Carbon Fiber assembly paste might help you.
https://www.universalcycles.com/shop...5&category=205

And/or, if your seatpost is alloy, maybe knurl the seatpost.
You can do this by hitting the post in a half dozen or so places around the post where the clamp tightens on the post.
Use a rounded or semi-pointed punch and a hammer.
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Old 03-07-18, 11:26 AM
  #3  
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IME bolts tighten harder than clamps.
Had a bike that was prone to post slip. But swapping the q/r for a (properly torqued) bolt stopped it cold.
Another option is to use something to improve grip.
Assembly paste is made for the job.
If you’ve got a gearhead friend, ask to be given a scoop of valve grinding compound.
Or try some toothpaste.
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Old 03-07-18, 11:35 AM
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Make certain that the post is the correct size and that the slot in the seat tube is not closing up when you tighten the clamp. If the slot closes up you are clamping the sides of the slot together and not clamping the post.
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Old 03-07-18, 11:35 AM
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Have you tried cleaning some of the grease off the post? Maybe there's too much on it.
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Old 03-07-18, 11:36 AM
  #6  
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you mean it's slipping down, rather than the saddle itself is sagging? (loose tension brooks-etc. , ridden wet can change shape)

I had the seat post slipping down on my Brompton folding bike, the seat post QR is part of the fold..

so I added a second QR, a band that gripped the seat post directly.. to fold the bike I just have 2 levers to open,

when I pull it up again I slide the other band clamp down & close the QR, to sit on top of the frame QR.

Is the solution i`m looking for as easy as getting a fixed bolt type clamp?
If you don't need the QR function for some reason, maybe so.. if its an MTB and you need the Seat drop for Gnarly downhills, maybe not..






.....

Last edited by fietsbob; 03-07-18 at 11:40 AM.
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Old 03-07-18, 12:24 PM
  #7  
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Originally Posted by trailangel View Post
Carbon Fiber assembly paste might help you.
https://www.universalcycles.com/shop...5&category=205

And/or, if your seatpost is alloy, maybe knurl the seatpost.
You can do this by hitting the post in a half dozen or so places around the post where the clamp tightens on the post.
Use a rounded or semi-pointed punch and a hammer.
Please don't do this. If the carbon paste doesn't work and you absolutely have to knurl your seat post, mark the area you want to knurl and tap it with the round side of a course half round file. Do it all around the post.
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Old 03-07-18, 12:30 PM
  #8  
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Clean and regrease the seatpost and inside of seat tube. Align the gap in the clamp with the gap in the seat tube.

If that fails you might try a heavy duty seatpost clamp like the Surly Constrictor. If that fails try a shim cut from a beer can.

Another option is a second seatpost clamp on the seatpost itself that keeps the post from sliding down.
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Old 03-07-18, 01:58 PM
  #9  
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Originally Posted by practical View Post
Have you tried cleaning some of the grease off the post? Maybe there's too much on it.
+1

I never grease the post. I grease down inside the seat tube, but the clamping area (top inch) remains clean and dry.
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Old 03-07-18, 02:41 PM
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My post was slipping even though I was careful to clean off stray/excess grease. It may've had to do with the seatpost being slightly bent back, by my weight (210lb) and the previous owner who was also a big guy. I just couldn't tighten it enough. So I used an old engraving tool I had lying around (the kind with a point that vibrates) and engraved knurled rings around the post in the action area. It fixed me right up.
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Old 03-07-18, 02:48 PM
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Knurling im familiar with is done on a Lathe, at a machine shop .. seatpost would be rotating and the Knurling tool pressed against it .
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Old 03-07-18, 02:53 PM
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Get a good clamp from Salsa. Don't over tighten, use a torque handle.
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Old 03-07-18, 03:05 PM
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Originally Posted by fietsbob View Post
Knurling im familiar with is done on a Lathe, at a machine shop .. seatpost would be rotating and the Knurling tool pressed against it .
If that's to me, then yeah, I know what you mean. I put the seatpost on a pole and rotated it while engraving, while using an old headtube cup of the right internal diameter as a guide. Unlike real knurling, I didn't end up with a grid of intersecting lines, but close enough.

Last edited by rseeker; 03-07-18 at 03:10 PM.
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Old 03-07-18, 03:40 PM
  #14  
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It`s a full susp MTB. I reposition the seat post every single time i switch bikes (due to climatic conditions) and using a quick release is therefore very practical. This could be as many as 10 times during a winter season and this being my backup bike it usually hangs up in the ceiling to get it out of the way. Thinking back it always used to slide like that. Not that much but enough to be annoying. It`s an old black Bontrager seat post and come to think of it the post surface may be too smooth to stay in place. I don`t know why people mention grease but i never treat that area with anything. Never. Maybe i could try sanding the seat post with a coarse grit or something to get the paint off?! So about that assembly paste, does it set or not? Heck, maybe lava soap would work, hahaha.
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Old 03-07-18, 10:53 PM
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Dropper seat posts Hold the Base steady, and the remote lever on the bar released the saddle to drop..
considered getting one?

'back in the day' they had a simple spring.. one end clamped the seat post, the bottom end was the frame , QR for the post..






..

Last edited by fietsbob; 03-07-18 at 10:56 PM.
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Old 03-08-18, 12:50 AM
  #16  
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What about getting a seat post that is properly sized to the seat tube?
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Old 03-08-18, 08:36 AM
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Originally Posted by leob1 View Post
Please don't do this. If the carbon paste doesn't work and you absolutely have to knurl your seat post, mark the area you want to knurl and tap it with the round side of a course half round file. Do it all around the post.
Your way for you please... makes you feel better, right.
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Old 03-08-18, 10:08 AM
  #18  
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Originally Posted by fietsbob View Post
Knurling im familiar with is done on a Lathe, at a machine shop .. seatpost would be rotating and the Knurling tool pressed against it .
Exactly. Knurling increases the diameter of the work piece slightly by displacing material as the knurling tool is forced against it. It's similar to rolling threads onto a spoke, where the threads have a diameter greater than the spoke blank. "Shot-peening" has a similar though smaller effect. Some good explanations and illustrations here: https://www.reed-machinery.com/pdf/kn...ata-master.pdf
Steve
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Old 03-08-18, 02:23 PM
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Ok - KNURLING - it is. KNURLING KNURLED KNURL. I have an aluminum seat post. Say i have this tool. Think it could work?

https://www.ridgid.com/th/en/close-q...tubing-cutters
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Old 03-08-18, 02:34 PM
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Old 03-08-18, 03:31 PM
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Yup, did that.. just didn't produce a video..
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Old 03-08-18, 03:41 PM
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Originally Posted by imobilinpedalus View Post
Ok - KNURLING - it is. KNURLING KNURLED KNURL. I have an aluminum seat post. Say i have this tool. Think it could work?

https://www.ridgid.com/th/en/close-q...tubing-cutters

you dont want to cut it off? Knurling leaves a diamond pattern , but when the point in the center of the diamond wears off it's a little smaller than it started off..


perhaps the seat post is smaller than the reamed inside of the frame? echoing 'road fan'..

to fix that get another seat post 0.2mm larger, then * using an adjustable reamer, shave out just enough

so the new seat post just slips in, and stop cutting..

I did this on a frame with a 27.0 seat tube to take 27.2 seatposts.. * (borrowed the tool the bike shop had, in the winter when it was quiet)
it is 0.1mm of difference radially, from tube wall..


have the new seat post in hand, of course..





Last edited by fietsbob; 03-08-18 at 03:45 PM.
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Old 03-09-18, 10:37 AM
  #23  
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Find a collar of some sort to put on the seat post so it can't go down any lower. A quick fix might be a hose clamp laying in your tool box. https://www.grainger.com/product/29N...180309163628:s

The link is just an example. You'll have to determine the correct size.
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