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Thread: Seat Post Trauma :(

  1. #1
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    Angry Seat Post Trauma :(

    Okay, so I got the RS Reverb for my birthday. Very pleased with it, however the LBS 'sensibly' (NOT) put grease on it even though the manual says NO grease. Anyway, the post dropped (during riding) as in it's main position - I know it's designed to drop! So I have tightened and stayed inside 6NM torque. I also took the grease off!! Grrrrr...Too tight and the seat post won't work, if not tight enough then it will slip down. I have tried friction paste but it slipped v slightly yesterday but was better.

    I took it back to the LBS and they have reapplied some friction paste and set it up to the correct torque. BUT they say that a creak I have is caused by post and frame not quite matching up absolutely exactly. This all sounds very odd, can it be right? Surely the 30.9 reverb seat post for the price will fit my aluminium frame properly. There is some movement isn't there due to the fact that the post is essentially two tubes.

    ...any experts out there...any ideas about what I can do? Apart from sell my dropper post

    Can't stand creaks, can't stand em!!

  2. #2
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    My assumption from your post is that the whole Reverb is slipping down your seat tube. Then, when you tighten the seatpost clamp to stop the Reverb from slipping, the bit of the Reverb that is supposed to slide, won't.

    If that is correct, then it implies that the seat tube clamp force required to stop the Reverb as a whole from slipping is deforming the outer Reverb tube and clamping the sliding part. I'm not doubting you at all, but when you think about all the bending forces that the Reverb has to undergo during use as your weight heaves about on the saddle, I'm astonished that the outer part of the Reverb isn't stiff enough to prevent it "clamping" onto the sliding part. I'm thinking that there must be a manufacturing error.

    Even if your seat tube is a bit oversized, and so requiring extra torque on the seat clamp bolt, most of that extra torque will be applied to deform the seat tube so that it clamps the Reverb, it will not be going into deforming the Reverb. The clamping forces required just to stop the Reverb from moving is the same whether your seat tube is a good fit or not. The extra force on the seat clamp bolt just makes up for seat tube oversize.

    So its the Reverb that's at fault!

    One last idea. Try wrapping cling film around your Reverb body, not too much obviously. That is not a tried and tested soultion, I'm just thinking "ultra-thin shim".

    Second "last idea". Your seat tube is not cracked is it?
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  3. #3
    Senior Member MTBLeague's Avatar
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    Is there any info on a "breaking in" period, sound like the force to hold it on the bike is obviously too much for it to slide up and down freely, could an incorrectly installed internal seal be causing this, it does seem wrong, would agree with steve from an engineers viewpoint.

  4. #4
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    Unhappy

    Sounds like my frame is not at fault then, phew!

    Nothing is mis-shapen, the reverb is brand new and certainly cannot see any cracks. Basically to recap if the seat post clamps too hard to the post then the up and down motion is restricted, and the clamp must not be torqued over 6NM. At this torque my post does not move properly, it sticks - so I suppose Steve you're right - the post could be at fault. I am being forced to tighten to less than 6NM to ensure the dropper moves freely.

    Here is SRAM's reply to the original problem:

    Hi Dom,
    Thanks for your email. If you're having trouble with holding the seatpost in the frame, remember to put some sort of friction paste in the frame, then torque the binder bolt as low as you can without having the post slip. Maximum torque is 6.7 Nm. If it's the bolts that hold the saddle on that you're having trouble with, make sure you're alternating between bolts as you tighten. torque to between 8-10 Nm. I would recommend servicing the post once a year.
    Thanks,

    Nate Newton
    SRAM USA Dealer Service
    www.sram.com/service
    www.worldbicyclerelief.org


    I have tightened the saddle bolts at the top. They seem fine. I am just bemused about creak between seat post and frame and as you say, the post is held by that main clamp. Seat posts don't require o ring style clamps all the way down the seat tube do they?!

  5. #5
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    Will inspect the seat tube later. I flipping hope it's not! Gulp!!

  6. #6
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    I'm answering my own questions here! I have just re read the SRAM email. He states quite clearly max torque is 6.7 NM, therefore implying that post can be clamped up to that amount...well when I clamp at 5NM, it does not work properly, and I have tried 6 too...therefore as you say seat post needs to go back I think. A max torque surely doesn't mean, flap about until you find a torque that works!!?!?

  7. #7
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    Wdll at least the reply was informative on SRAM's part! Could be the LBS's fault for applying grease originally?
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  8. #8
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    Yeah but they've taken the grease all off now and I have also checked it's gone and we have the friction paste on now too. Perhaps have to see how it goes tomorrow.

  9. #9
    Senior Member Tazzedx's Avatar
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    Have to agree with Steve. It's also worth remembering that a creak heard from around the seat post area is not always the seatpost. It can come from a number of locations around the bike as sounds travel through the tubing. This can be noise from the BB, cranks , pedals, seat post, and even the handlebars and stem.

    Though in this case it does seem as if it is from the Seatpost. Good luck.
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  10. #10
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    Unhappy

    Okay, reporting back. I have news:

    Firstly no cracks in my frame - used my night light and all looks well. In fact nice and clean, looks as good as when new. Looked up and down seat tube and where welding is, no bad signs

    Secondly, used my torque wrench set to 5NM, on that torque it tightens up the post really well, no creaks!! Just fitting snug, as you'd expect but the dropper does not work, it gets stuck, and that's at a whole NM less than max torque. At a lower torque, as in loosing the clamp bolt from the 5NM setting, the dropper works again as it should but the creak (ill fitting post) becomes apparent - so no doubt it will slip down at some point, a creak just means movement doesn't it as the end of the day, all sound is caused by vibration. So I think Steve is right, the flipping post aint working properly. I mean, correct me if I'm wrong but 6NM is not a lot is it??!!? I'm pretty sure my torque wrench is okay!!

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