Slipping seatpost
 

New seatpost. An aluminum polished dropper post. Going into an aluminum bike.

Both 30.9, double checked with calipers.

First install, used light grease on the post as normal. It slid down a bit while riding. I tightened it as hard as I was comfortable with cranking, Most likely way over torque. It still lost a little elevation throughout the rest of the ride.

I revisited the installation and cleaned up the post and reinstalled with fiber grip. Again, I coupled that with serious ham fisting.

Same result, it’s slightly sliding down.

This hasn’t drastically affected my rides because all good stuff is done with the dropper down. Still irritates me that it’s slipping.

So I’m thinking about whatever my third attempt will be. It’s always a hassle due to the internal routes dropper cable.

I don’t have room on the frame for a standard 2 bolt seat collar.

I have noticed that the surface of this new seatpost is just a lot more polished than my old one. I think that’s the problem. I’m considering scratching it up with course grit sandpaper. I don’t love the idea that this would remove material. If it didn’t work it could make the problem
worse.

I did discover a double clamp that would fit, one side goes directly onto the post, and the other over the frame. Seems viable, but a little bit bulky. Obviously installed with plenty of fiber grip.

Anything else I should try while I wait for the new clamp to arrive?

install it completely dry, including removing the gunk from inside the seat tube.
report back

I would try a thin shim strip. Current soda cans are really thin.

try a double-bolted and wider seatpost clamp?

So I don’t have the room between the top of my seat tube and where I have the first weld to fit a wide clamp. That was my first idea.

Ive been eyeing this thing

https://cimg2.ibsrv.net/gimg/bikefor...c5bb774bda.png

It would clamp the post and the frame. Seems like a nuclear option.

Salsa Post-lock:
https://www.salsacycles.com/cdn/shop...867&width=1100
This is a rack mount that attaches to your seatpost. But you can use it to stop your post from sliding down.

Haven't personally tried it, but I have heard of valve grinding compound being used for a slipping seatpost. It is available in various grits at most auto stores.

Instead of sanding you could texture the surface by making hundreds of small divots with a sharp centre punch.

I could see that for a standard seatpost. I’m not going to hit my brand dropper with a hammer.

If it's a round seat post you can add some texture by rolling it on a flat surface while pushing down on a wood rasp to do the rolling. Target the area that will be under the seat clamp with a little bit more each way up and down.

Basically you're doing sort of a DIY knurled texture with the rasp, which has teeth & not fine cutting edges as would a file. May not need much to effect a more solid clamping, but you can always do more if a little isn't quite enough.

For my geometry and riding style, the 175mm dropper I got was more than enough.

I wonder if I should have gotten the 225. If I hubbed it all the way down to the collar, then used the tool free adjustment option to reduce it down to about 210mm, it would probably be the right height with nowhere to slip. I wonder if that’s what they expect people to do.

Could be.

Does it look 'used' yet?

Maybe you can return it in exchange for a different size?

If nothing else I'd let the vendor know what it's doing that maybe it shouldn't be doing.

That 'tool-free adjustment' collar thing looks a lot like the tripod leg adjusters I'm more familiar with. There may be an element under the collar that's designed to add 'stiction' when the ring's tightened. If the element's not quite right you won't get enough friction to hold the inner shaft tight.

Never over-tighten a dropper post. It will interfere with the dropping. One trick I read somewhere is to put a condom on the seatpost, and then stick that in the seat tube. Ideally, it should not be a used one, and it should not be lubricated.

Also look at the asymmetrical designed Campagnolo brand seatpost clamps. Might be worth a shot as well.

Use an automatic punch with the spring dialled back? Although I like spclark knurling idea.

Loctite 641?

We have used this without any damage, 120 for serious and 220, it's just usually silicon carbide or aluminum oxide in a petroleum grease.

I received a reply from PNW several days ago. Their suggestion was to avoid carbon paste since it can sand through anodized surface and lead to corrosion causing a stuck seatpost. This is contrary to the advice in the FAQ of their own website. Their suggestion was that if the new weird seatpost clamp doesn't work out then I can contact them for an exchange. The idea being that standard black might be a teeny bit grippier than the silver I have.

I took out the post again and replaced the clamp with the weird red one pictured earlier in this thread. It fits perfectly and essentially doubles or more than doubles the clamping surface area. That is extremely encouraging but it doesn't seem as heavy duty as the OEM Canfield clamp I had. I don't take drops with my seat up, it hopefully won't matter. Despite manufacturers advice, I did reinstall it with a small bit of carbon paste.

I truly hope that's the end of it. I hope it'll be a year or two before I have the post off again.

Show us a good close up picture of your current setup.

When you have everything all tight, is the gap between the clamp all the way closed. Or if there is a gap in your seat tube, is that all the way closed by the time you are finished tightening your clamp. If either, then you need to figure out why that gap isn't there. Once the gap is closed, the clamp can't get make the seat tube any tighter on the seat post.

It's also possible that if the bolt you are tightening is a shoulder bolt, then other things that are wrong, might have the nut bottoming out on the shoulder before the clamp is fully tight. Similar can happen with other types of bolts and fastener designs.

I once over torqued the seat post clamp while on a ride and the tightening screw broke in two. Not having a spare with me, I walked to a nearby farmers house and managed to 'borrow' a stainless steel hose clamp that worked until I had to bring my bike in for a new drive train. I didn't ask for it to be replaced with a real seat post collar, but he did it anyway.

Are we being ribbed here?

For your pleasure.

All those years following the Dead around with the 1962 VW Bus with the split windshield really paid off.

I have this. Unless I am mistaken, it is a conventional seat post clamp that attaches to the seat tube, which is why it has that lip at the top.

From the horse's mouth:
https://www.salsacycles.com/products/post-lock