Bicycle Mechanics - Seatpost not completely clamped down

I recently mounted a seatpost onto a Leader 725TR with grease, and it still turns a little from side to side, even if I clamped it down all the way. It might even be slowly sliding down. I used Polylube to grease it. Did I use the wrong type of grease, and would Loctite work? Thanks in advance!

just need a light wipe of grease , as a corrosion barrier, done regularly, did it stay OK when it wasn't greased so much ,
like it's dry fit,
or is this perhaps an undersized seatpost?

Sight unseen all I have is questions .

Frame and seat post both aluminum? Google on bike doesn't seem to help much.
Suggest removal of grease completely and rechecking frame ID and seat post OD.
You may need another 0.2mm of SP diameter, or even 0.4mm. You might consider
using the CF seat post lube which is designed to provide a bit of grip. DONOT use
loktite unless you want a permamount. Surface area here is huge compared with
threads and you will have a really big time removing it.

It was a little bit better without the grease, but I thought that it might eventually corrode together. What's a good CF lube? The seat post I got was from a Draft that I used to have. It's just a temporary post until I get a Thomson. Maybe the diameter of the post is a bit smaller since the Draft wasn't all that great?

Theres specialty stuff for CF , take the bike to one of the many bike shops in SF ,

they can See the situation and have better informed suggestions..

There is a stepped Tapered tool that can be inserted in the frame to see what the seat tube post Bore is.

they should also have the specialty Carbon type bike stuff to make post fit best.

I'll get it checked out. Thanks!

A seatpost should be a tight running fit into the frame before clamping. If the seatpost is small enough to drop in very freely it's probably slightly undersized though not necessarily a full size smaller. It's also possible that your frame was reamed slightly oversize, contributing to the problem. As others have noted the grease is an anti corrosion barrier, but obviously will increase the required clamping force.

Before you do anything check that your clamp can close completely. Tighten and look at both the slot and clamp ears and make sure nothing is touching and keeping the clamp from closing fully onto the post.

Here are two options to try, assuming that the next post size (+0.2mm) doesn't fit.

1- do not grease the post. Instead start by using some solvent on a rag to clean the post and inside of the seat lug area. Then carefully reach down and apply grease to the seat tube starting about 2" down. Insert the post using some twist motion to spread the grease as you go, but be careful not to go too deep and pull it back up. Now you'll have an anti corrosion barrier for most of the length, but the clamping area will be dry contact and provide better traction at lower force.

2- use medium grit lapping compound available at automotive stores as seatpost "grease" Lapping compound is abrasive grit in a grease base, so it'll provide the same protection as grease would, but the grit will provide mechanical engagement between the post and frame and greatly improve clamping traction. Lapping compound was the remedy of choice to improve clamping hold for years before carbon assembly paste existed.

The clamp is an integrated clamp, so I can't do too much about it. It can clamp down all the way, and is currently clamped down all the way. The post does slide down freely, but there is a little bit of resistance along the way. Not too much, though. It sounds as if the two steps would work. I'll try that first. Thanks.

Edit: Would a tiny shim or something at the clamp area work?

It sure sounds to me like you need to find the correct size of seat post more than anything else. Especially if you're tightening the integrated clamp until the slot is severly tapered towards the top of the frame. That taper indicates that you're actually bending the seat tube to a new shape and that is never a good thing on an aluminium frame. You could try a wrap around shim of pop can metal but you don't want to just use a little sliver of it jammed in because that'll actually strain the tubes from trying to bend to fit and at the same time will actually reduce the contact area. If a nearly full turn does not fit then your post is just one size too small. I've used the pop can trick before but it was to fit a post that was .4mm undersize.

Solution solved with a piece of metal shim, and very minimal grease on the clamp area. Thanks for all your help!

Solution solved with a piece of metal shim, and very minimal grease on the clamp area. Thanks for all your help!

Congrats on solving the problem. Be aware that if shimming worked, or was even possible, you almost certainly have the wrong post. No concern as long as it works, but if you find it creaks, that's because it isn't supported over the entire length.

I wouldn't post at all but you had mentioned considering buying a new post. Before doing so, find out the right size so it'll fit and clamp properly without special measures.

Alright. I'll get it checked out for sure. Thanks.

Alright. I'll get it checked out for sure. Thanks.

your clamp and seat tube are probably ovalized from clamping on the smaller post. can be reformed by
carefully driving a wedge in the slot in seat tube, starting at the top and pointing down the tube. i used
a large flat point screw driver. had a bike with a 27.0 post in a 27.2 seat tube.