Persistent Problem...

[I_paint]

It seems that my carbon seatpost is slipping through the seatpost clamp. I'm riding a Cervelo Soloist Team. This has been happening for awhile now, as I ride the seatpost gradually slides through the clamp, no matter how much i tighten it. I recently ordered a seatpost shim from Cervelo, which solved the problem, for a little while. After my ride today I noticed that the flanges on the seatpost shim were bent upward, apparently the seatpost is now sliding through the clamp a bit, and sucking the shim along with it! (It didnt slide as much, and might not slide any further, but still...) This is getting to be really annoying, since nearly every ride the seatpost slides a few millimeters, even a centimeter sometimes, and I'm constantly thinking "WTF why is my seat feeling low again?" Should I try using something like Locktite, or some other threadlocker?

 

[bikecoach]

When cadel evans was riding for T-Mobile he had the exact same problem. To solve it he used some lock-tight on his seat post.
Another method which has been used is getting a sports drink powder and mixing it with water to make a thick sticky syrup. Paste a bit of this along your seat post and once it dries your seat should stay put.

 

[graphixgeek]

I know with Cannondales with carbon seatposts, they sell this lube for them that increases the friction between the seatpost and the frame to stop the slippage. This lube goes against the usual recommendation of NOT lubing the seatpost in any way. It is possible to crank down on a carbon seatpost and crack it (doesn't sound pretty either). Maybe you need to clean the seatpost and inside the seat tube. Good luck!

 

[capwater]

I know with Cannondales with carbon seatposts, they sell this lube for them that increases the friction between the seatpost and the frame to stop the slippage. This lube goes against the usual recommendation of NOT lubing the seatpost in any way. It is possible to crank down on a carbon seatpost and crack it (doesn't sound pretty either). Maybe you need to clean the seatpost and inside the seat tube. Good luck!

Lots of people realize that you don't lube a carbon seatpost, but if it is a replacement then you had best get the grease out of the inside of the seat tube.

 

[Unbelievably]

I suggest that you clean both surfaces with isopropanal.
Use a scotch-brite pad on the seat post around its circumference.
This will remove the sheen that IMO is causing the slippage.
Wipe down with the isopropanal again and reinstall with your desired hight.
You might want to apply an auto wax to the exposed scratch marks.

You want to keep the surfaces dry and free of contaminants.
This means no lubes, thread-locks or gatoraid...

P.S.
perhaps you may have overtightened the clamp,
compressing the post...

 

[I_paint]

I suggest that you clean both surfaces with isopropanal.
Use a scotch-brite pad on the seat post around its circumference.
This will remove the sheen that IMO is causing the slippage.
Wipe down with the isopropanal again and reinstall with your desired hight.
You might want to apply an auto wax to the exposed scratch marks.

You want to keep the surfaces dry and free of contaminants.
This means no lubes, thread-locks or gatoraid...

I got the bike used (somebody traded it in at a LBS), so I dont know what the previous owner did to it. I took the seatpost out today, and there is a thin film of something slippery, probably grease. I had noticed it when I put the shim in, but that seemed to fix things for a little while so I sort of forgot about it. Makes sense though.

P.S.perhaps you may have overtightened the clamp,
compressing the post...

I hope not, that would be a disaster. It doesnt look compressed, or cracked, but the slippage has scraped off some of the clear coat where the clamp puts the most pressure on it. I've been careful not to torque it ridiculously tight, since it shouldn't need to be torqued super tight anyway.

 

[Albert 50]

When cadel evans was riding for T-Mobile he had the exact same problem. To solve it he used some lock-tight on his seat post.
Another method which has been used is getting a sports drink powder and mixing it with water to make a thick sticky syrup. Paste a bit of this along your seat post and once it dries your seat should stay put.

You're having a lend of us....surely.

I would have no doubt the method described would work till the gunk got wet & softened. Also if this flawed suggestion was used on an alum frame the salts & sugars which are in all sport drinks would cause severe corrosion

 

[gclark8]

Problem solved: http://www.cyclingforums.com/t361070.html

 

[I_paint]

Cleaned everyting, seat tube, shim, seatpost... and the problem persists. What gives??

 

[gclark8]

Cleaned everyting, seat tube, shim, seatpost... and the problem persists. What gives??

like I said in my previous post:

One leading CF frame maker supplies a little aluminium sleeve for the CF steerer tube and a 2 pack of epoxy, the same method will fix the sliding seat post problem....

Epoxy a 50mm sleeve of Al tubing inside the seatpost where it is to be clamped.

 

[I_paint]

like I said in my previous post: Epoxy a 50mm sleeve of Al tubing inside the seatpost where it is to be clamped.

You mean inside the seat-tube, or on the seat post?

What kind of aluminum tubing are you talking about here? Something I can cut out of a beer can, or something I'd need to get at a hardware store? I'm not sure I like the sound of using epoxy, since thats a rather more permanent alteration to the bike. But if it works....

 

[kleng]

After my ride today I noticed that the flanges on the seatpost shim were bent upward, apparently the seatpost is now sliding through the clamp a bit, and sucking the shim along with it! (It didnt slide as much, and might not slide any further, but still...)?

The fact the seat post is sucking down the shim means the seat tube is a problem, as there must be a tight bond between the post and the shim, otherwise the post would slide down the shim.

I hope there isn't a crack in the seat tube, that expands allowing the shim to move down even though the clamp is appears tightly done up.

How are the threads of the seat post clamp, have they been stripped at all, any small amount of play under stress (your weight on the saddle) might cause them to open a little bit.

 

[gclark8]

You mean inside the seat-tube, or on the seat post?

What kind of aluminum tubing are you talking about here?

Something I can cut out of a beer can, or something I'd need to get at a hardware store?

I'm not sure I like the sound of using epoxy, since thats a rather more permanent alteration to the bike. But if it works....

First:
fit the seat post to the frame,
measure how much of it goes inside the seat tube,
remove the seat post from the frame,
measure the ID of the seat post, (the one in my hand is 22mm),
buy some suitable Al tubing, the OD just under the seat posts ID and wall thickness of at least .8mm, this may be some old 22.4 Al flat bars you can cut up.
Cut off a 50-60mm length, see if it is a friction fit in the seat post, you may have to sandpaper a bit here,
mix up the epoxy,
slide the sleeve coated in epoxy up the seat post so one end of it is about 20mm above the clamping ring,
allow 24 hours to set,
refit the seatpost,
clamp up as a normal Al seat post.

 

[kleng]

I can't believe Cervelo don't have an answer to this problem, their reknown for the their frame engineering and attention to detail, if the shim doesn't work I would go back to them for a solution. Its just strange we need to revert to these home remedies to get things to work as they are supposed to in the first place.

 

[fauxpas]

I don't believe this. One of my fears when I returned to cycling was that at 110kg (242lbs) , the 'seat-to-post', or 'post-to-seat tube' may cause some issue. But they haven't. My last bike was supplied with alloy seatpost. No issue. I bought a carbon seatpost, no issue... and that's not overtightening anything. That's at standard or lower than standard tightness.

If it is a cervelo issue, I could only see it as an issue for them if they made the seat tube out of such strong stuff, the clamp cannot apply appropriate pressure...

If weight is not an issue, you could drop a tube around the same thickness as the seat post, down the seat tube all the way, only allowing the actual seatpost enough inserting to be at the correct height. You would need to drill some holes in the tube you drop in to aid future removal...