Tandem Cycling - Capt' seatpost problem

I'm having a major issue with the captains seat post not staying in place!

OK, so I'm a Clyde, but still I don't have this issue on any of my other bikes. After a couple of miles it will twist a bit and then just start dropping. We've tried to tighten in - to the point of actually snapping a bolt - with no success. Short of drilling a bold hole through the tube, does anyone have any suggestions?

Try some carbon fiber assembly paste, it is kind of gritty and helped on my Trek Speed Concept when the seat post was slipping. It solved the problem. Most LBS have it.

Wayne

You might consider using a product such as Tacx Carbon Assembly Compound (http://tacx.com/en/producten/fietsgereedschappen/Carbon_pasta/index.dot) to create extra friction between the seatpost and the frame.

Are you sure that you don't have a dimensional mismatch, or a stretched collar which is allowing the clamp to bottom out at the joint and not getting tight enough. Locktight makes a sleaving compound that might work, but might make the joint a little too permanent.

What are the bike type and seatpost size you are using?

Are you sure that you don't have a dimensional mismatch, or a stretched collar which is allowing the clamp to bottom out at the joint and not getting tight enough.
This would be my suspicion as well. On one of my bikes (a Trek MTB) the factory original seatpost is just a bit on the loose side and prone to slipping. Inserting a sleeve cut from a soda can cured the problem.

You might consider using a product such as Tacx Carbon Assembly Compound (http://tacx.com/en/producten/fietsgereedschappen/Carbon_pasta/index.dot) to create extra friction between the seatpost and the frame.

This solved the problem on my carbon road bike for me.

OP, check with your LBS and see if they can, KNURL the post, the stroker seat post on our new Trek T-900 hybrid tandem was doing that and they had a way, (tool), to make a indenting gripping surface on the slick seat post, they called it "knurling" the post, FYI. Sorry photo is facing the wrong way but you can SEE the pattern the knurling tool put into the seat post, NO slippage at all now.
http://i41.servimg.com/u/f41/16/61/22/60/dscn0011.jpg

Aluminum seat posts can indent from the tight seat post clamp. You may not be able to see the indentation but if you wet your fingers and run then down the seat post you can probably feel it. If you have calipers available you could measure for an indentation. Another possibility is a seat post slightly too small. If you had this problem from the beginning then the seat post may be too small in diameter even though it is marked the correct diameter. Trying another seat post to see if it slides down would answer that question. I would not drill a hole through the tube to put a bolt in. The top of the seat tube is a high stress area and you could break or bend the seat tube causing expensive damage to your frame. The compounds mentioned above could be used if the seat post is the correct size.

If you get desperate, you can try a hose clamp or something like this:

http://www.origin-8.com/?page_id=91&short_code=Post+Saver+Seat+Clamp&cl1=SEAT+POSTS

So Im thinking if I knurl the post, add a coke can shim, coat it in carbon paste and hold it all together with an Origin8 seat clamp i should be good!

Alu beer or pop can shim works.

If you can get an aluminum can shim into the seat post it would pay to see if a larger post would work.