Alum seat post slipping

it's obviously best to have exactly the right size post for your frame.
Do you?

Ideally, the post should fit in there like a piston.

what frame do you have?

overtightening the bolt all the time could bust your frame.

Its a haro vgf v4. 27.2mm seatpost fits it fine, like a glove. Oh, btw..when I said shim I meant QR bolt/shim.

Blademun said:

Hi, I recently bought a american classic aluminum seatpost for my bike and it is slipping, Alot!

Before I greased it it would slip like a couple Cm every mile..after greasing, it will slip down all the way on the first big bump I hit. Very annoying since my bike is a small frame and with it all the way down my legs are all bunched up.

I can't tighten the seatpost bolt anymore. Its also not the original seatpost shim, which I broke awhile ago. It came off a iron horse bike I belive.

Try de-greasing it.
It might be that the post is too thin, in which case cut your losses and get the next size up. Any kind of technical fix could damage the frame or bottom bracket.

Don Shipp said:

Try de-greasing it.
It might be that the post is too thin, in which case cut your losses and get the next size up. Any kind of technical fix could damage the frame or bottom bracket.

If he is using the correct size, than trying the next size up does not wash.

Blademun said:

I can't tighten the seatpost bolt anymore. Its also not the original seatpost shim, which I broke awhile ago. It came off a iron horse bike I belive.

Well, maybe that is the problem, not the post, assuming post is correct diam for seattube?

Try a new clamp with a new post. The allen key type is more reliable: http://www.pro-bikegear.net/content/products.php?id=011617&lang=en

Also, when clamping, line up the gap in the top of the seat tube with the gap in the clamp.

boudreaux said:

If he is using the correct size, than trying the next size up does not wash.

But
If the bolt is as tight as it will go, and the post still slips, that would indicate that the post is too small
Unless
the bolt (a replacement) is the wrong sort which is why it can't be tightened any more.
I'd need to see it.

Obviously either the post is the wrong size or there is something wrong with the clamp. You should get someone who knows what they are doing to sort this out for you. Do not degrease the post. It's esential that there be some sort of barrier between the post and the frame.

Regards Jay