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The last time I used my folding bike I gave it a thorough clean, and used WD-40 on the moving parts and then lubricated them again with a silicone-based lubricant spray. This is an eleven-year old Brompton model with the regular non-extended seat post.

Yesterday when I tried to use it, the seat post kept sliding down whenever I hit a bump in the road. I assume some of the WD-40 or the lubricant got on the post and now it is too slippery for the clamp to get sufficient grip on it.

What would be the best way to get rid of the slipperiness and restore the necessary friction between the seat post and the clamp? Is there a household product I can use for this, like soap or talcum powder maybe?

4 Answers 4

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This page from an Australian Brompton retailer suggests 3 options (you've probably tried the 2 first ones):

  • cleaning the seatpost and the tube with isopropyl alcohol.
  • tighten the clamp (by one quarter of a turn on the nut that is on the opposite site of the lever)
  • replacing the seatpost sleeve: Bromptons have a plastic seatpost sleeve, that is a considered to be a wearable part. If it is contaminated, replacing it may be the option. It requires special tools though, as the previous one has to be shredded to be removed — so better to see with a Brompton specialist.
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I assume you’ve tightened the seatpost clamp sufficiently? The professional way to increase friction for seatposts is by using carbon installation compound.

You could try to remove all oil/grease with some alcohol or dish washing detergent.

But keep in mind that seatposts often corrode and are hard to remove after some time if they are not installed with grease. Probably not an issue on a folding bike if the seatpost is lowered and extended regularly.

When it comes to houshold items, I guess you could try tooth paste instead of carbon installation compound. Toothpaste contains small particles and can be used to polish things. I guess this should increase friction. Any other polishing paste might also work.

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  • 1
    the seatpost in a Brompton is part of the folding "mechanism". Any solution involving paste might not work in the long run, as the seatpost is being moved each time the bike is folded/unfolded.
    – Rеnаud
    Mar 6, 2022 at 16:22
  • Tightening the knurly nut opposite the release lever by a quarter or half turn before closing the lever might do the job.
    – Carel
    Mar 6, 2022 at 16:40
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I had the exact same problem on my Brompton. When riding for long distances, the seatpost would gradually slip and move downwards. Thus, if I had the correct seat height at the start of the ride, I would no longer have it at the end of the ride.

The cause of the problem was that the quick release seatpost clamp wasn't tightened enough. The spec is 4-7 Newton meters and mine was closer to the low value than the high 7 Nm value. The torquing needs to be done with the clamp closed.

I torqued it to 7 Nm. This solved all my problems. At 7 Nm, it requires a very strong hand to close the clamp, so it's no longer as easy as it was with 4 Nm. But the seatpost doesn't slip anymore.

If you have any oil or grease on the seatpost, use isopropyl alcohol to clean it. On non-folding bikes with a permanent seatpost clamp, you would use grease on the seatpost to prevent it from jamming there forever, but on folding bikes like Brompton with a quick release clamp, there should be absolutely no grease there.

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  • Wow, 7Nm for a seatpost clamp definitely sounds high, but I guess they made them extra strong for daily use. I’d worry about the quick release lever breaking at some point (assuming it’s a normal one).
    – Michael
    Mar 7, 2022 at 6:47
  • @Michael A good measure of the force is bolt preload. Torque is dependent on bolt thread size. If you have two bolts with same preload, but different thread size, the one with larger threads has more torque.
    – juhist
    Mar 7, 2022 at 16:36
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Mine's a cheap folder and the seatpost has knurling around the end.

Likely this is because the tolerances were too sloppy and the knurl has expanded the metal enough to add grip. But as the ridges of the knurl wear off, it gets sloppier again.

I ended up shimming it with a strip of brass shim stock. One could also use aluminium from a softdrink can which is thicker.

This is probably not your answer because Bromptons are not knurled, but may be relevant for future readers.

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