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Seat post keeps sliding down!

rapid_donkeyrapid_donkey Posts: 448
edited April 2013 in MTB general
I have a Giant with the standard Giant connect seat post and QR clamp.
When I bought the bike it all worked fine.
Before xmas I bent the seat post with a dodgy landing and replaced it with another new Giant connect.
When I fitted it I put grease on the shaft to prevent it getting stuck in the frame. The seat post kept sliding down, so I have wiped away all the grease on the post, as much as I can out of the frame, and do the clamp up as tight as it physically goes. My seat still drops. Today I had to stop and adjust it 3 times on a 12 mile ride.
Im no bloater at 82 kg's. Anyone got any suggestions?
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  • nicklousenicklouse Posts: 81,520 Lives Here
    it the seat post the same size?
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • ilovedirtilovedirt Posts: 5,798
    Strange, mine sometimes does that if I put too much grease on it, but stops if i wipe it off.
    Production Privee Shan

    B'Twin Triban 5
  • Perhaps definetly check if the new seatpost is the right size as this may be what's causing the seatpost to fall down?
  • bennett_346bennett_346 Posts: 5,092
    Bad QR possibly, i used to have one that came with my bike that didn't clamp the post enough despite having to use a rediculous amount of force to close the lever. Replaced it for a good clamp and it grips fine now.
  • batmobatmo Posts: 277
    I had this problem and replacing the clamp was the answer.

    Of course, I am a bloater...
    Viscount Grand Touring - in bits
    Trek ZX6500 - semi-retired
    HP Velotechnik Spirit
    Brompton M6
    Specialized Camber Comp
  • The replacement seat post is the exact same item as I bent, same length and width.
    It could be the seat clamp, just strange as it was working fine before.
    What seat clamps to people rate?
  • bennett_346bennett_346 Posts: 5,092
    I personally rate the Hope QR seatclamps, but i got mine for £5 in halfords, not sure i'd pay the full RRP :lol:
  • 2x102x10 Posts: 79
    I put a turn of electrical tape around mine, problem sorted, and Im super bloater!
  • When I had this problem with my XTC a cheap m part bolt up clamp cured it.
    2006 Giant XTC
    2010 Giant Defy Advanced
    2016 Boardman Pro 29er
    2016 Pinnacle Lithium 4
    2017 Canondale Supersix Evo
  • I use a HOPE QR and it holds my Thomson post fine .... never slipped ....
    Rocky Mountain Altitude 50 (+ upgrades.....!)
  • Quick update on this thread as its become a really annoying problem!!

    I tried to put a small amount of tape around my seat post, but it never stayed on when I fed the post back into the bike.

    I have disassembled the Giant QR clamp, fully cleaned and regreased it, still made no difference.

    As this has all only occured since I fitted the new Giant seatpost, Im hoping it is that. When the seatpost is in the frame, there is a bit of lateral movement without the seat clamp tightened.
    Im going to take the post into work tomorrow and measure it with some digital calipers.

    I really hope it is the post, otherwise could I have possibly stretched my frame with the dodgy landing that bent my original post?

    I did buy the post from an eBay seller for £15. Depending on tomorrows measurements, Im wondering if it is genuine...
  • WindyGWindyG Posts: 1,099
    I would try a standard bolt clamp first rather than the QR one.
  • GiraffotoGiraffoto Posts: 2,078
    When the seatpost is in the frame, there is a bit of lateral movement without the seat clamp tightened.
    Im going to take the post into work tomorrow and measure it with some digital calipers.

    I strongly suspect you'll find it's the wrong size. There should be zero lateral movement but smooth up-and-down movement when the clamp's not done up. Also you could have got one for less than £15 and the right size from several places - On-One and Superstar spring to mind
    Specialized Roubaix Elite 2015
    XM-057 rigid 29er
  • ljs1977ljs1977 Posts: 247
    Degrease the post and the bike and the clamp.

    Apply carbon assembly paste to post in lieu of grease.

    Report back.
  • .blitz.blitz Posts: 6,588
    As above carbon assembly paste: http://www.wiggle.co.uk/ritchey-liquid-torque/

    There's enough in that sachet for several seatposts/bars
  • It was suggested by my LBS that I try some fiber paste on the seat post, but its an option I would like to use only if it comes to it.

    So, this morning I measured the width of my seatpost with digital calipers.
    It is supposed to be 30.9. Along the length of the post, I am measuring between 30.79 to 30.81. I am guessing that could make a difference. It is 30.8 where my seat post sits in the clamp on the frame.

    I have now ordered another Giant Connect seatpost but from a Giant dealer this time. It was still only £20.
    I went for the Giant one as it comes in 375mm length, instead of getting a 400mm and cutting it down.
    However, if the new seatpost also measures short on width, I will be sending it back and getting an aftermarket post.
  • stubsstubs Posts: 5,001
    Did you measure the frame internal diameter sometimes they can be reamed oversize by mistake. I would just make a shim out of a coke can.
    Fig rolls: proof that god loves cyclists and that she wants us to do another lap
  • +1 for assembly paste... no brainer
  • Another update on this thread.

    I recently bought a 3rd seatpost, a Giant connect SL: http://www.fulfordcycles.com/giant-conn ... 3311-p.asp which still slipped down, so I also replaced the Giant QR clamp with one of these Hope clamps: http://www.evanscycles.com/products/hop ... tch__plid_ and with no grease on the post and everything done up, it is still slipping.

    With the Hope clamp done up reasonably tight, it slips. With it done up ridiculously tight (on the verge of not being able to close it), it does just about stop the seat post from slipping down. However, where the clamp sits on the frame of the bike and is pinched together when you close it, it has taken the lacquer and paint off the frame and its down to bare metal after 1 ride.

    Does anyone else have to do up their seat clamp stupidly tight?

    Final thing to do now is buy some of that Ritchey liquid torque paste and see if it makes a difference. I have left this option to last as every time I ride the bike, I usually take the seat out for it to fit in the car.

    I weighed myself with all my riding kit and a full camelbak today and Im 83kg, cant see why this might be happening.
  • bennett_346bennett_346 Posts: 5,092
    Something is the wrong size. There is no other reason i can think why it would do that. I've got a hope seat clamp and it barely requires any force to keep the seat up even with a greased post.

    I am guessing that whatever caused you to bend your old seatpost has also malformed the seat tube slightly and either the clamp doesn't fit properly or the post doesn't make enough surface area contact to be held up.
  • cooldadcooldad Posts: 32,601
    Something like this^^^^^^^^^^^^^^^^^
    I am chunkyish and have never had that problem on any bike, ever.
    And I can close the QR with a finger, with the post greased.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • cooldadcooldad Posts: 32,601
    I see you've also put on a kilo since the first post - stay off the pies.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • Whilst staring at the bike and wondering what else it could be, I had an idea.
    I have spun the clamp 180 degrees, so the cutout slot in the clamp is inline with the slot in the bike frame.
    With a little grease under the clamp and on the seatpost, Ive just been out for a quick 30 minute ride and with the clamp up reasonably tight it hasnt slipped. Will have to wait until I hit more gnarly stuff to see if its sorted.
    Anyone else run their QR clamp slot inline with the bikes?
  • ddraverddraver Posts: 22,590
    On a hope clamp? Yes, to be honest super duper tight

    Fibre paste is your friend
    We're in danger of confusing passion with incompetence
    - @ddraver
  • bennett_346bennett_346 Posts: 5,092
    You're doing it wrong then.
  • ddraverddraver Posts: 22,590
    Are nt really too many ways to do it bennet...

    As good as Hope's stuff can be, Hope QR's are not the best...
    We're in danger of confusing passion with incompetence
    - @ddraver
  • Having just typed 'Giant Trance X' into google images, and filtering only the large pictures, all the pictures I can clearly see actually show the split in the seat clamp facing rearwards, lining up with the split in the frame. Have I been running it backwards?
    Some example pictures:

    http://www.bigbike-magazine.com/media/g ... nced-2.jpg

    http://www.flickr.com/photos/egf/3280580289/

    http://farm4.static.flickr.com/3129/258 ... 0045_b.jpg

    http://www.paulscycles.co.uk/smsimg/4/m ... ancex3.jpg

    I can see how it could make a difference. The clamp pinches together exactly where frame is split for such movement.
  • bennett_346bennett_346 Posts: 5,092
    ddraver wrote:
    Are nt really too many ways to do it bennet...

    As good as Hope's stuff can be, Hope QR's are not the best...
    What? I don't think you've read/understood what i've said.

    Go back and try again :wink:
  • ddraverddraver Posts: 22,590
    I repeat - there are nt too many ways to do it ( well I ve seen some on the internet, but I always come back to the traditional methods myself...)
    We're in danger of confusing passion with incompetence
    - @ddraver
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