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#16
09-22-2011, 07:47 PM
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Great input guys...thank you very much. I'll start with the carbon paste and then rough up the posts clamping area if the paste doesn't work by itself. As I mentioned, I have this exact same combination on another bike and never had this problem.
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#17
09-22-2011, 08:29 PM
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I had this problem with one of my seat posts. I tightened the crap out of it and it is staying in place now. I don't know why it's doing that. I have to assume a defect of some sort. I have no problem with my other 3 bikes. The only thing I could think of was that I was pushing back on the saddle (which I'm sure would happen through out a ride) and that is what would move it. I mean, your butt is the only thing that touches the saddle right?
PS: I don't have a big butt. I'm 6ft 1in and 175lbs. Quote:
__________________
Martin 85 Merckx 753 00 Serotta CSI 00 Tommasini Sintesi
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#18
09-22-2011, 10:16 PM
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Quote:
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#19
08-19-2018, 07:53 PM
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Had this problem, as well, with a two bolt system. I put a dab of Gorilla Glue on the contact areas of the clamp and tightened down snug. Rode 65 miles. Problem solved!
Last edited by Jeff N.; 08-20-2018 at 09:00 AM.
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#20
08-19-2018, 08:27 PM
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It sounds like a tolerance problem between the two parts.
The contact surfaces are so small I don't think carbon paste will fix it. 1. Clean all the grease off. 2. Wrap the rail with thin 2 sided tape. 3. Ride. If it doesn't slip then you can trim the tape with a scalpel so it doesn't show.
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#23
08-19-2018, 10:23 PM
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Ultra uses carbon paste in his seatposts clamps. Works great for stuff like that. Had the problem once.
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#26
08-20-2018, 08:55 AM
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"Plenty snug" may not be the torque spec. If the post is designed to fit those rails, then I think you only need some carbon paste and a torque wrench (I rarely tighten up to the max torque, but have had to do so on a Deda post to get it to hold firm).
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#27
08-20-2018, 09:04 AM
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I had this issue with a Moots post. it was fine on the road but if I rode singletrack or cyclocross with it (it's a CX bike) it would slip back. like a full centimeter during the course of a race. not acceptable.
I contacted Moots and their advice was, I kid you not: "tighten it more." I basically did what everyone else here advises. re-grease the clamping bolt(s), clean all contact points, torque to spec.
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#28
08-20-2018, 09:21 AM
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I've had this problem before... chances are the inside/outside radius of the saddle rails + clamp do not match up perfectly or as someone mentioned the clamp could have been overtightened or something.
You say you have the exact same combo on another bike with no issues but unless you bought the 2 saddles + seatposts at the exact same time they could be slightly different. I would not expect Shimano to change the seatpost without changing the model # but my experience is saddle manufacturers change stuff up subtly all the time without necessarily calling it a new saddle, and most saddles don't have a model # that could be used to differentiate a slight change anyway. The other thing is do your two bikes fit the same. It's not about your butt being big or anything but if you have a fit on one bike where you're using the forces of pedaling to push yourself back against the saddle then that bike would be more likely to cause you to see this problem. That force could easily be > 100lbs if you're strong and the fit is weird. This is one of the things that makes me fearful of ISPs... if the ISP does not have the ability to swap out the clamp parts it can be incompatible with some saddles. Trek and Specialized get this right with their side clamping posts/masts that allow you to change the "cups" to fit different rail shapes. I would still try the carbon paste but if it's really slipping bad it might not help. Last edited by benb; 08-20-2018 at 09:24 AM.
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