Slipping seatpost

crescent

Does anyone have any top tips for stopping an aluminium seat post from slipping? I have a Trek Domane AL3 and I cannot ride any more than about 10 miles without having to adjust the seat post. I have tried roughing the seat post slightly with some sand paper but it hasn't really helped, and now just looks a bit tatty into the bargain. Clamp is torqued correctly (7Nm). Would assembly paste help? Even though it is designed for carbon.
Thanks for any advice. Cheers.

whyamihere

Assembly paste should help. There's nothing about it which means it should only be used on carbon. It's also worth measuring the seat tube on the frame and the seatpost in case one or the other is out of spec. Your bike should have a 27.2mm seatpost, and both the post and the frame should be very close to that. If the post was out of spec and measured 27.1mm for example, you're going to have problems, the same if the frame tube is too large. Replacing the seatpost is easy, if it's the frame then it would be a warranty issue.

photonic69

I had a slipping post on an old bike. It was a quick release clamp on a MTB. Nothing I did would stop it from slipping. It was so annoying as 1" up or down from my position it was fine. I believe the post was deformed at some point in the past by over-tightening. I put a new, cheap post in and it cured it. I then sold the bike.

Munsford0

My first proper road bike had a carbon post in an alu frame. That used to slip till I started using assembly paste. Now I use it on all my seat posts regardless of material or frame

crescent

Will give the paste a try. I think I may end up changing the post for cosmetic reasons at some point, it's not that badly roughed up but still looks a bit tatty.
Thanks for the suggestions. Cheers.

veronese68

Seatpost on my bike would slip when i first got it, ali post in an ali frame, tightened it a bit more, then a bit more until the bolt in the clamp snapped. Replaced the bolt and was more careful but it still slipped. Wasn't aware of assembly paste at the time. Replaced the clamp with another one, either Thompson or Salsa can't remember now as I've bought both in the past, didn't have to tighten it much and no more slipping.

sungod

as above, assembly paste

if the post is really a bit too small, you could apply one or more thin dustings of clear coat (i.e. https://www.amazon.co.uk/dp/B009G1AU3Q ) to slightly increase the size, and then use assembly paste

crescent

Good shout. I think I have some matt black spray paint kicking around, could maybe tidy up the appearance and increase the diameter slightly. Cheers.
I know I could probably just buy a new seatpost for a few quid, but I would like to fix it - its personal now 😀

de_sisti

crescent said:

Does anyone have any top tips for stopping an aluminium seat post from slipping? I.

If you're not too snobbish, one of these will work.
https://www.screwfix.com/p/easyfix-blue-zinc-plated-hose-clips-12-20mm-10-pack/22153?kpid=22153&ds_rl=1249413&gclid=CjwKCAjwscGjBhAXEiwAswQqNG3dhWjKvyYk5msGe16z7aeKDoWqUxF9M64hyti8NsJlRQVHxbbCGxoC74sQAvD_BwE&gclsrc=aw.ds

masjer

As well as most of the above suggestions.

Try cleaning the clamp bolt (check for thread damage too) and clean the threaded part of the clamp. Regrease/anti seize the bolt threads. A dry bolt imparts less clamping force than a lubed one for the same torque.
Make sure the clamp lines up with the slot in the frame.
Although it sounds counterintuitive, a lightly greased seatpost is less likely to slip (only use on a metal post/frame) and stops seizing due to corrosion, or use carbon paste.