Slipping seat post totally doing my head in!

[Nautonier]

Firstly, apologies that said stem is in fact on a road bike. Ritchie WCS carbon post on a Spesh Tarmac carbon frame with carbon clamp. Didn't slip for over a year at 6nm (with no carbon paste) and now it slips down every ride by about 20 - 40mm. Here is what I have tried:

1. Using a torque wrench and tightening it up to the recommended 6.5nm.
2. Using Morgan Blue carbon paste
3. Swapping out the carbon seat clamp for an alloy one
4. Over tightening the clamp to 8nm (and also my sphincter while doing this...)
5. Cleaning off the carbon paste and making sure all surfaces are spotless

None of these work; the post slips down slowly over 20 - 40km. At the end of this mornings ride, the seat had slipped down about 45mm as well as skewed around about 25 degrees, and that was tightened up to 8nm.

Has anyone else had this problem or can suggest something else to try as I'm all out of ideas and a slipping seat post is a sure way to ruin a ride. I'm not sure I want to just keep tightening it more and more as something will eventually give and if it's the frame, that would be an expensive mistake and straight to "confessions from the f^^&kwits"...

I read some reviews on the carbon paste I purchased and it seem to work for others, but for me it has the same effect as vaseline...

 

[creaky]

Morgan blue isn't the most aggressive carbon paste out there but I have never had a problem with it. It does scratch components less.

The weird thing is nothing has change from what you've said, it just started slipping. No visible damage / cracking to the post or seat tube ?

I wouldn't tighten it more tbh. Can you borrow / swap out to another post to try for a while ?

 

[John U]

My BIL sent a very valuable frame to a shop for a build. Shop cracked frame at seat tube during build. I understand your sphincter clenching. Be careful overtightening!

 

[Nautonier]

Morgan blue isn't the most aggressive carbon paste out there but I have never had a problem with it. It does scratch components less.

The weird thing is nothing has change from what you've said, it just started slipping. No visible damage / cracking to the post or seat tube ?

I wouldn't tighten it more tbh. Can you borrow / swap out to another post to try for a while ?

There is no visible damage at all, the bike hasn't been crashed or dropped. I'd simply set up the seat post and left it for a year (and about 3500km riding), but the problems have begun since I took it on a plane recently and had to loosen off the seat post clamp and lower the seat.

I have another seat post, but I can't see why one would slip and another wouldn't.

The guys at my local spesh shop suggested using a combination of tightening 1nm over spec and using carbon paste. Can't remember if I've tried that combination yet, I think I did have it at 7.5 at one point with paste and it was actually slipping from side to side as I was riding (aka the vaseline effect).

I am missing something about how to use carbon paste? I thought it was simply a case of smearing a bit on the seat the the seat tube and tightening to spec.

 

[SF Trailboy]

I am missing something about how to use carbon paste? I thought it was simply a case of smearing a bit on the seat the the seat tube and tightening to spec.

I'd suggest applying liberally to the post all over, below the insertion point. Think back to when you where a teenager....:tape2:

 

[Flow-Rider]

I am missing something about how to use carbon paste? I thought it was simply a case of smearing a bit on the seat the the seat tube and tightening to spec.

I let the carbon paste dry out over night before installing the seat post when I have the time to waste. What I have found with some carbon posts is that they flex in the centre and collapse over time, people keep on tightening them till the frame cracks. You can also try an offset seat post clamp if you don't already have one.

 

[Nautonier]

I'd suggest applying liberally to the post all over, below the insertion point. Think back to when you where a teenager....:tape2:

Now that's taking me back

I think I may be on a one way trip to the fuckwits thread after all. Just as I got all excited about the idea of letting the carbon paste dry overnight, I noticed that my Tarmac was sitting right on front of my S-Works Enduro and the posts were in roughly the same position. Something was wrong with this 'double image' and I realised that the the clamp on the Enduro, which also has a carbon frame, was sitting at exactly 180 degrees different from the clamp on the Tarmac. In other words, the clamp bolt was at the front, where the split in the seat tube is. On the Tarmac it was at the back...

So, is it possible that these clamps are designed so that in order to work effectively, the clamp bolt always has to be aligned with the split in the seat tube? Or does this make no difference at all, the mechanism tightening evenly all the way around irrespective of where the clamp bolt is positioned? It is entirely possible that when in transit recently, the clamp on the road bike spun around 180 degrees and I didn't notice it when I was jetlaggedly putting the bike together...

 

[ming]

Yep, off to the fuckwits...
The split in the clamp has to align with the split in the frame. If it doesn't, then the clamp has to actually slip against the frame to tighten.
This is why we can't spin the clamp around to keep the mud out of the threads.

Ming

 

[pink poodle]

^ which is also why a forward facing slit is a good idea.


You may have worn off some of the post with your year of paste free penetration, leaving it slightly under size.

 

[Nautonier]

^ which is also why a forward facing slit is a good idea.


You may have worn off some of the post with your year of paste free penetration, leaving it slightly under size.

Yes, it's something that causes me great concern in a wider context.

 

[Minlak]

With my Thomson seat post collar the carbon frames have the split of the collar at the front and the alloy frames have the split on the collar facing rearward..

 

[Fatherpaul]

Try googling it to see if you pick up some tips from the net. I found this one:
https://www.youtube.com/watch?v=GWYERtOBFI0
Tape just above the clamp as shown on the youtube clip should help.

 

[bear the bear]

Know anyone with a set of callipers to check the sizing of the post and seat tube?
If the tolerance is too great then time for a new post

 

[Nautonier]

With my Thomson seat post collar the carbon frames have the split of the collar at the front and the alloy frames have the split on the collar facing rearward..

View attachment 331704

OK, so maybe I haven't gotten it horribly wrong. The split of the collar is at the front on my Tarmac (I've now put the bolt on the clamp to the front) and on the Enduro it has 2 splits on either side (with the bolt at the front). I'd honestly never thought about seat clamp position in relation to collar split position, now I'm totally confused! I've always just installed them the same as they came from the shop new, so haven't had to assess the logic behind it. But it's very possible that my Tarmac clamp did rotate 180 degrees.

 

[Nautonier]

Know anyone with a set of callipers to check the sizing of the post and seat tube?
If the tolerance is too great then time for a new post

I could try and borrow some callipers, but I doubt that an expensive seat post used for less than a year would have become 'crushed' to the point where it has collapsed a fraction. Surely the seat clamp would accomodate a minimal reduction in diameter? The collar split isn't closing right up.

 

[Nerf Herder]

Why would you need to spin the collar around for carbon? That doesn't make sense ? I would have thought it was all mechanical with the seat clamp aligned with the expansion slot to compress the tubing... What's the material got to do with binding? To use Transition Bikes lexicon we are just binding TITs :tape2:

With bars, some manufacturers glue/bond a grit section on to the clamping area of the bar to allow the stem plate to grip a bit harder ... Might also get you back to tolerances if your post has shrunk due to un-pasted post usage :noidea:

 

[bear the bear]

I could try and borrow some callipers, but I doubt that an expensive seat post used for less than a year would have become 'crushed' to the point where it has collapsed a fraction. Surely the seat clamp would accomodate a minimal reduction in diameter? The collar split isn't closing right up.

IAOI the interface was at the limits of tolerance to start with, usage may have caused it to exceed this?!?!?!
If you can't then you will have to swap out the seat collar and post to check for the culprit.

 

[Martin.au]

Yep, off to the fuckwits...
The split in the clamp has to align with the split in the frame. If it doesn't, then the clamp has to actually slip against the frame to tighten.
This is why we can't spin the clamp around to keep the mud out of the threads.

Ming

***Goes to check my bikes***

Mind you, mine are aluminium and I suspect that the clamp on mine will still work.

 

[cokeonspecialtwodollars]

For QR clamps try a little lube on the cam mechanism, for bolt up put a little grease or anti seize on the thread this will mean that you're not adding friction of the thread to your torque, also when was your torque device last calibrated?

 

[pink poodle]

Why would you need to spin the collar around for carbon? That doesn't make sense ? I would have thought it was all mechanical with the seat clamp aligned with the expansion slot to compress the tubing... What's the material got to do with binding? To use Transition Bikes lexicon we are just binding TITs :tape2:

With bars, some manufacturers glue/bond a grit section on to the clamping area of the bar to allow the stem plate to grip a bit harder ... Might also get you back to tolerances if your post has shrunk due to un-pasted post usage :noidea:

One way or another this all comes down to friction...if the unpasted use has caused enough friction the outside diameter of the post may have been reduced.

I think the answer is to hit the post with a really rough grit sandpaper...to scuff the surface.