Seat post keeps sliding down!

rapid_donkey

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?

nicklouse

it the seat post the same size?

ilovedirt

Strange, mine sometimes does that if I put too much grease on it, but stops if i wipe it off.

MTB1997

Perhaps definetly check if the new seatpost is the right size as this may be what's causing the seatpost to fall down?

bennett_346

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.

batmo

I had this problem and replacing the clamp was the answer.

Of course, I am a bloater...

rapid_donkey

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_346

I personally rate the Hope QR seatclamps, but i got mine for £5 in halfords, not sure i'd pay the full RRP

2x10

I put a turn of electrical tape around mine, problem sorted, and Im super bloater!

The Spiderman

When I had this problem with my XTC a cheap m part bolt up clamp cured it.

The Rookie

GT QR's are really good quality!

BigAirNig

I use a HOPE QR and it holds my Thomson post fine .... never slipped ....

rapid_donkey

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...

WindyG

I would try a standard bolt clamp first rather than the QR one.

Giraffoto

rapid_donkey wrote:

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

ljs1977

Degrease the post and the bike and the clamp.

Apply carbon assembly paste to post in lieu of grease.

Report back.

.blitz

As above carbon assembly paste: http://www.wiggle.co.uk/ritchey-liquid-torque/

There's enough in that sachet for several seatposts/bars

rapid_donkey

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.

stubs

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.

Chinley Churner

+1 for assembly paste... no brainer

rapid_donkey

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_346

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.

cooldad

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.

cooldad

I see you've also put on a kilo since the first post - stay off the pies.

rapid_donkey

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?

ddraver

On a hope clamp? Yes, to be honest super duper tight

Fibre paste is your friend

bennett_346

You're doing it wrong then.

ddraver

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...

rapid_donkey

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_346

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

ddraver

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...)