I have tried with carbon paste and w/o. I am only tightening to 6nm which is what the collar says. Seatpost is a Thomson and frame is an Aspero.
by marlborolane
I have tried with carbon paste and w/o. I am only tightening to 6nm which is what the collar says. Seatpost is a Thomson and frame is an Aspero.
by marlborolane
23 Comments
Have you checked the diameter of the seat tube and the seat post?
Try laying a thick coat of carbon paste and make sure it’s close to the collar.
Get in touch with Cervelo and alert them to the problem. Ask if they’ve got recommendations for posts. They may just tell you to take it to a dealer. But it’s worth asking in case there is a known issue.
The Salsa Lip lock is a taller clamp which I’ve used when posts have moved on me.
Do you trust your torque wrench.
Then there’s the old Paris-Roubaix trick of putting another clamp above the seat collar.
Did you clean the grease out of the frame?
Why don’t you have the original seat post in it?
Just tighten it more
Had the same issue with a steel frame. Frame was on the upper spec limit and no seatpost did fit. Bought a shim and a smaller seatpost. Fixed it for me.
Carbon paste
Ah, good ol’ Cervelo Famously known for tight manufacturing tolerances…
If carbon paste doesn’t cut it, a round of tape (exp. Gorilla tape) will increase the diameter of the post enough to get enough friction. A cleanup afterwards is difficult, but it will stay in place.
They make these wacky double clamp seat collars if you can’t find another solution.
https://www.amazon.com/KCNC-SC-13-Seatpost-31-8mm-27-2mm/dp/B00FOFPK7O
Are you pushing maximum density? I don’t mean are fat, just maybe you’re very well built with muscle. I’m 6’4″ and weigh 21 stone all muscle, and I have problems with seat posts. In my case though I’m riding steel or Aluminium frames so no problem with going a bit tighter. Wondering if maybe you could dip the seat post into something to add a permanent shim. An oxidising process or maybe Aluminium blacking to bond a layer. That extra micron thick layer could give grip.
Confirmed your torque wrench is in spec? I’ve taken sand paper and roughed the clamping area of the seatpost up a bit with success.
Thomson sells 27.4. That is how I solved this issue in the past. Might still have the post if interested. How long do you need it to be?
a taller clamp is probably the best option. annoying though, those are nice seat posts
Which type of carbon paste did you use?
I think if the fit is already pretty snug, the grit in the gritty types tends to get scraped off on assembly. But I recently got some Motorex carbon paste and it is a clear, sort of gel-like substance that is supposed to provide grip without grit — bonus that it doesn’t scratch the surface finish.
Fixed a similar situation on an old steel bike by scuffing up the alu seatpost with rough sanding paper around the clamping area. While all the usual tricks failed, that’s what solved the problem for good.
Where is the slit in the seat tube in relation to the bolt in the clamp?
I had this issue on an old MTB and turning the clamp around so the bolt was spanning the slit rather than being opposite it helped.
Had this problem on my old bike, a thin layer of friction tape wrapped around the seatpost where it sits inside the frame (in combination with friction paste) solved the issue.
Can you try roughening the seatpost with 80 grit sandpaper? Only in the clamping zone.
It’s possible to have a combination where the seatpost is slightly under-sized and the frame slightly over-sized, and it can make it difficult to stop slipping with just friction paste.
It could be as little as 0.05 mm out of spec, so nominally both the frame and seatpost are correct size. You can measure it if you have a good digital caliper that is accurate to 0.01 mm.
If so, you could try slipping a good old beer can shim between the post and the frame. Or you could get one of those double-clamp seat collars, but I personally don’t like them because they look so bulky.
Time to buy a new bike
I don’t have a particular solution with regards to getting the grip beyond the double collar method that others have mentioned. That actually seems to be the best solution in your case.
The only other solutions I can suggest trying are either (one or both):
1) Use a different brand of carbon gripper paste. The data might be hard to find, but different brands have different granule sizes. If you can find a smaller granular size of the gripping material, it might not wipe off as easily during insertion.
2) Using a rough grit sandpaper, lightly sand the clamping area of the seatpost, moving AROUND the circumference of the seatpost. Don’t stroke up and down along the shaft like you’re beating meat. The idea is to score the clamping surface enough to create some grip for the seat tube to grab on to, and prevent the seatpost from sliding down. Additionally, these little valleys created by the sanding may hold the carbon gripper paste granules in place better, giving them a little valley to sit into. Make sure gripper paste fully covers any exposed aluminum though, as the exposed aluminum can weld to the carbon seat tube via galvanic corrosion without a layer of grease.
I did want to comment though: I noticed you have an Áspero, as do I, and I want to warn about continually tightening to the max torque load that’s specified on the collar as 6Nm. It’s very common for the threads in the collar to get pulled completely out with the bolt over time. I had loosened and tightened mine about a dozen times since ownership (I’m original owner), always using a torque wrench and tightening to 6Nm. I’d heard many stories about other Áspero owners stripping out this collar thread in the Áspero owners group on Facebook, so I was ultra cautious about it.
Last year, around this time, I took the seatpost out to clean out the frame completely, as mud and grime managed to collect inside, and I had stripped all components off the frame to install Ride Wrap and to run new cable lines. However, upon re-tightening the seatpost clamp, I noticed the bolt thread was extending much further past the thru hole on previous attempts, and I was only around 4-5Nm at that point. It felt like the thread was already beginning to strip.
I managed to get it up to 6Nm, but left it alone and ordered a spare, just in case. At that point, it wasn’t a question of IF it would strip, but rather, WHEN.
I made another adjustment of seatpost height at the beginning of this year when installing a new saddle, so another loosen / tighten cycle. The bolt extended even further past the thru hole, but was still able to make it to 6Nm.
And then 2 days ago I had taken out the seatpost to do a cleaning so that I could apply some RideWrap on it to attach a saddle bag, and as I tightened the clamp bolt, at 4.5Nm, I heard a very loud SNAP. It honestly sounded like carbon had cracked, it was so loud. I looked at the bolt in the collar, and there it was: A pile of aluminum pulled out around the bolt shank. Collar completely loose.
Thankfully, I had the spare backup, and as soon as I put it on, I went online to purchase another one. However, I noticed all the new photos of the part show it with a silver (stainless) bolt rather than the black bolt on both of my units.
So, out of curiousity, I contacted Cervelo via their contact form to ask them if perhaps there might have been an update/improvement on the part to increase durability.
Unexpectedly, two things came of the discussion:
1) The tech suggested that the 6Nm is only a MAXIMUM load, and to tighten to a lower torque if possible. Use carbon paste to maintain grip at lower torque. He recommended tightening to 5Nm instead, and going on a light ride to see if it slips. If it slips, increase torque gradually until the slipping stops, without exceeding 6Nm.
2) He asked me for a copy of my purchase invoice and address, and popped another replacement collar in the mail for me.
He never did answer if there was a change in the part, but I may be able to see it once I receive it.
People can say what they want about Cervelo, but after-sales support like this solidifies the brand in my mind.
What torque are you setting the screw to? Are the threads in the clamp damaged? Is that an aluminum shaving I see near the screw?