Sliding Seat Post!?
Alright, need a little advice...
My seatpost keeps sliding down no matter how hard I crank the bolt tight. I have a 07' Salsa El Mariachi with all Salsa components. My old 97' Rockhopper had a quick release that never slipped any suggestions?
It's possible that the top of the seat tube or the sp bolt mounting has been deformed enough that tightening will no longer work. Look to see if there is there is no longer a gap in the back of the frame when the bolt is tightened. Once the two sides meet all you will accomplish is further damage. Should cost nothing to have a shop look at it - hard thing to diagnose online.
If you got the bike used (doubtful with an 07) or replaced the seatpost, check the specs on your bike to make sure you have the correct size seatpost (there are many seatpost sizes). Check the slot in the frame and the clamp to make sure there isn't something stuck in there preventing it from tightening. If the bike is new, bring it back to the shop and have them look at it.
I had to shim a Thomson to fit a new Cannondale, and yes it was 27.2. The shim is a piece of beer can. Put a strip of thin aluminium inside the seat tube, hold it there while sliding the post in, clamp it down and ride.
Permanent Refugee .......
If you are using a newer style bike seatpost collar as opposed to the seat lug style of years gone by, do this.
Take the collar off the bike and take the binder bolt out of it.
Put the collar in a vise and with a fine toothed file, file away some of the collar where the two ends join. Often times the end of the collar that gets "pulled in" is too long and the result is that even though you have tightened the collar, as much as it will tighten, you haven't actually tightened it down on the post since the two ends of the collar are meeting.
I have had to do this with FSA and CAmpagnolo collars.
Always works for me.