Seat post slipping...

I'm having lots of problems with my seat post slipping. We thought we had it resolved, and I just checked it after several rides, and the *$%^ thing has moved again. Basically, over 40 miles or so, I lose .5 cm in height. We're replaced the clamp to the one the mechanics recommend. They've measured the tube and the post, and both are the appropriate size. Most recently, we put carbon paste on the post, and that seemed to help (until now). My LBS is at a loss. It's a 2006 Trek 520 with the stock seatpost.

Any ideas??

CA

I have a black piece of electrical tape where the seat post meets the seat tube. It goes around the entire circumference of the seat tube. I had slippage issues until I tried this trick. It seems too easy of a fix and like it would never work, but it sure has for me. For about 1000 miles now. Good luck and let us know if it works for you.

PS - It's also a nice way to mark that perfect seat height.

Sadly, I'm already there. The seat post was slipping so much that I marked the height with electrical tape all around. Now, I know it's slipping when the tape starts to bunch up:rolleyes::cool:

Thanks for the suggestion, though:)

CA

There was a techncial article on the velo news web site a while back about this. Apparently, you're not alone. One of the pro teams solved the problem by going to the hardware store and buying a hose clamp. You might want to try searching Leonard Zinn's archives. If I remember right (and the caffeine has not kicked in yet this AM), it was in spring, around the time of Paris-Roubaix.

I had this problem but not on a seat post, but a piece of equipment I was trying to qualify. You can get a set of feeler gages if you are feeling (haha I made a funny) like you need to find the exact gap, or you can go with Teflon tape. Find where you want the seat to be and mark that spot (that will be inside of the tube spot) then wrap up and down about 1/2 inch on either side of the spot with Teflon tape. It sounds like you have a gap and Teflon tape, while slick, will often fill the gap as it is thin. I find electrical tape might be too thick. It also might be that the tube is opening a little while you ride due to the stresses on the bike, which your bike shop should ask Trek about. Did you look for any (I'm sure you have) damage to the tube like a vertical crack? These sometimes are invisible and when you apply force to the seat and stir it around, it will open up (this happened to my first Gary Fisher I had, I guess it got mushed in transit). In that case I returned the bike and got a new one, but you can't do that here. Hope you figure it out. That sucks. My new GF does it once in a while but it is because I haven't cranked the clamp down.

I have the same problem on my commuter, a Trek 7200 fx, but I've decided to replace the seatpost as it has a suspension, which I really hate (it feels like it's eating all my energy on hills!!!). While I'm at it I'll replace the quick release with a regular bolt. Hopefully that will solve the problem, otherwise I'll have to look for Teflon tape.......

I haven't had this problem, but I would think a hose clamp would be a great idea- the usual seatpost clamps really only apply pressure at the bolt or lever side, while hose clamp applies force rather evenly all the way around.

ah...

is the hose clamp supposed to replace the seatpost clamp? Or is it supposed to go above it, preventing the seatpost from slipping into the tube?

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Originally Posted by OakLeaf

ah...

is the hose clamp supposed to replace the seatpost clamp? Or is it supposed to go above it, preventing the seatpost from slipping into the down tube?

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Above. See ( http://www.velonews.com/article/74577 ). There is a picture about 3/4 of the way down the article. ( http://www.velonews.com/photo/74584 )

I'm not sure how they used it, but my mechanical instinct says the replacing the seatpost clamp would be stronger. The clamp would create a 1/2 in grasping all the way around to bear the weight and hose clamps have a greater adjustability range, which I think is the main advantage. Granted, the seat tube acts like a seatpost clamp essentially since it's a notched cylinder- you get more force near the notch holding the post than on the other side of the tube. If you put the hose clamp on the post which still using a not quite snug enough post clamp, you're letting the edge of the hose clamp touching the edge of the seat tube bear all of the weight, which I'd be a bit hesitant about. Maybe if you had a second clamp of the thickness of a seatpost clamp it would be ok, but hose clamps are thin with lots of holes and I think it'd eventually buckle under the force (or at least have the potential too).

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Originally Posted by Thorn

Above. See ( http://www.velonews.com/article/74577 ). There is a picture about 3/4 of the way down the article. ( http://www.velonews.com/photo/74584 )

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That is priceless. A $5000? bicycle requiring a 50 cent, non carbon fiber, hose clamp? I'm sure it works. I've successfully used a hose clamp to "patch" a broken rack (still works). :p