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Recently finished my first “frame up” custom build. Absolutely love the bike except for one issue: The seatpost keeps slipping down inside the seat tube. Frame is an ’07 LeMond Poprad made from True Temper OX Platinum steel. The seatpost is an aluminum Thomson Elite. The clamp itself is a chrome Bontrager model that came with the frameset.
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Trek/LeMond states the seatpost O.D. should fall within 27.12 – 27.20 mm. Using dial calipers, my Elite measures exactly 27.20 mm (typical Thomson precision!). Haven’t checked the I.D. of the frame yet, but there is almost no detectable slop when inserting the seatpost – seems like a perfect sliding fit.
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Each time I reset the seatpost height, I’ve progressively torqued the binder bolt a bit more. Even at a whopping 125 in-lb, the seatpost will still head south. And yes, there is plenty of gap left in both the frame’s key hole slot and clamp so they’re not bottoming out.
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Granted, I’m a few double cheeseburgers away from being a <st1>Clyde</st1> (195 lbs) and ride on some pretty rough roads. But still, my MTB hardtail sees much worse abuse and never slips. Oh yeah, as standard procedure, I did grease the seatpost with Park Polylube.
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At this point, I’m rather perplexed! One solution is to add a second clamp directly on the seatpost. This would then rest against the upper lip of the stock chrome clamp. Together, the pair of clamps should easily solve the problem I suspect.
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Does anyone make a clamp with a size 27.2 mm I.D.? If not, I was thinking of getting a seatpost shim and cutting it down to the height of the second clamp (see photo below). I know there are some real experts here, so any other easier remedies would be much appreciated as well (like maybe knurling the seatpost, using a special grease, etc.)
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TIA,
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Paul
 

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Just get a new seat post clamp and see how that works. Since you're not running a carbon post, you can clamp the sh!t out of it, and something like the Salsa, with it nice, big bolt will do the trick nicely. You're going to crush a post before crushing the seat tube, but that's pretty much a non-zero chance with the Thomson.
 

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chamois creme addict
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Try some "Carbon Assembly Paste"

I would suggest trying some of the so-called carbon assembly paste. This stuff is basically a gelatin-like goop with little plastic spheres embedded in it. Kind of like liquid sandpaper. The plastic spheres compress and increase the friction between the seatpost and seat tube.

It is sold by Tacx - Carbon Assembly Paste, Ritchey - Liquid Torque, and FSA also calls it something else. I think it is all teh same stuff. Ritchey claims a 30% reduction in torque to achieve the same level of fastening, so in your case it it should be a 30% increase in holding power.
 

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eminence grease
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azoomm said:
Wait... I thought duct tape fixes all. Maybe hair spray is the bizarro duct tape.

Either way, apply more force.
The three Prime Items to fix everything are duct tape, baling wire and galvanized drywall screws.

Pump hairspray is the 4th.
 

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Make a shim out of a pop or beer can. Cut it to 1x4 inches, round out the corners. You might have to experiment with the size. Put a light coat of grease on both sides of the shim. The trick is to get it to go down the seat tube with the seat post without it falling all the way down, or having some of the shim sticking out on top. I had this very same problem with Thomson seat posts. I stopped using them as they don't have enough setback, even with the setback model.

I learned this from an article by Lennard Zinn. If you drink pop or beer it won't cost you a cent. Worth a try.

Or buy a different seatpost. I use an Alpha Q carbon and I have to use a little force to get it down.

AH- I now see that you are using a shim. Since you don't have a carbon bike or seatpost, just clamp the cra* out of it.
 

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terry b said:
The three Prime Items to fix everything are duct tape, baling wire and galvanized drywall screws.

Pump hairspray is the 4th.
Why would you use galvanized drywall screws? They are used in interior applications and go into either wood or light gauge metal studs... what benefit does the galvanization do?

Oh... I see... it's because of that which makes it magical. Got it :thumbsup:
 

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The problem with a Salsa seatpost clamp is that you have to crank it hard - you should try a good Y-allen wrench (3, 4, 5 mm), so you can torque the bejessus out of your seatpost and your seat tube AND your seatpost clamp.

You ought to call Thompson and Lemond (made by Trek) and see what the deal is. I had a decent aluminum seatpost slip (Ritchey WCS), but it was the clamp - the bolt in the clamp was stripped. It took a lot of elbow grease to get the old clamp off and to get the new clamp on - I finally used a rubber mallet (Reynolds 853 seat tube).
 

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Two scoops of inertia.
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The rattling cobblestones notoriously take their toll on forks, seatposts and bottle cages, and Slipstream has a few tricks up its sleeve. Two weeks ago the camp held a two-day “Cobble Camp” on Roubaix’s sectors, and found that the constant jarring was causing seatpost slippage. To combat this, the mechanics have affixed metal hose clamps — the same you might purchase at a hardware store — to the base of each riders’ seatpost.

“We have them right at the collar. Yeah, it’s a pretty stock piece, but that post isn’t going to slip at all,” Hopper said.
link for pics
 

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eminence grease
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azoomm said:
Why would you use galvanized drywall screws? They are used in interior applications and go into either wood or light gauge metal studs... what benefit does the galvanization do?

Oh... I see... it's because of that which makes it magical. Got it :thumbsup:
They don't rust, so if the thing you repaired with them ends up at the bottom of the sea, it will stay repaired.
 

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Take some of the grease off untill it is just a very light coating. Also make sure the bolt and bolt head are greased so you are getting and accurate torque value and not just bolt head friction. Greasing the inside of the seat collar also can help allowing it to slide on the paint as is is clamped down.

If all else fails reef the crap out of it.
 

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Seat post slipping solution?

I'm researching the market for a seat post lock ring. Basically it would sit above the seat post clamp to keep carbon seat posts from slipping back into the frame. It would be extremely light (approx. 8 grams), but would serve the purpose as needed. They might also be convenient for people who have to remove their seat post for travel purposes. It would be an easy way to 'set' the height of your seat.

I realize that there are pastes and such out there now, but my question is do you think there's a market for this type of clamp solution?

It would be available in 27.2 and 31.6mm sizes.

Your thoughts?

Dan Dakin
www.chasebicycleproducts.com
 
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