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Old 10-28-10, 09:34 AM   #1
Fleetdog
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Seat Clamp Loosening

The seat clamp on my cross bike is giving me some trouble. About a month ago it loosened up at a cross practice pretty much on impact of a flying remount where I displayed particularly bad form (even by my own low standards). At the time I was sure I had stripped a bolt or the threads the bolts go into. I took the thing apart and I couldn't see any damage to any of the threads and everything threaded together smoothly so I just put it back together, tightened them down and rode it.

I had no more problems until last night. Riding the course at a local park I noticed my seat making a lot of creaking noises at the start of lap 2. By the start of lap 3 my seat was sliding front to back pretty freely in the clamp. Again, I took the clamp apart and inspected the threads. Everything looks good. The bolts screw in easily and don't seem to have any play in the connection.

Is this just something that normally vibrates loose occasionally so I need to tighten them down regularly or is this an indication that something is screwed up in the clamp and I just can't see it?
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Old 10-28-10, 09:53 AM   #2
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So what are you looking at for your next seatpost?, since this (unstated)
one is obviously not doing the job.

some : traditional 2 bolt Campag are proven, though bolt heads on top scheme
works best, easiest, with leather saddles.
I have some of the prior American Classic seatposts too..
they bored out the inside non round to be beefier to resist bending better

and Race Face has a bolt to clamp the rails,
and a separate bolt via linkage that adjusts the angle .

Some saddles dont have much clearance over the rails,
so seatposts need to have the clamping mech low profile,
RF is one in that column..

Last edited by fietsbob; 10-28-10 at 10:01 AM.
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Old 10-28-10, 01:04 PM   #3
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I'm not looking for advice on a replacement. I'm trying to figure out if this is a defect or if it's just a case of me needing to pay more attention to tightening it occasionally.
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Old 10-28-10, 01:57 PM   #4
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You wrote "I just can't see it? " .. well .. I can't see it either ..

Still no clues as to what brand and model of seat post you are talking about,
So go to a bike shop and they can see what the heck you are talking about, then.
I expect Madison has several.
Given you assume too much of the list, without sending any pictures and detailed information,
you are on your own...

Good luck.

Last edited by fietsbob; 10-28-10 at 02:18 PM.
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Old 10-28-10, 02:27 PM   #5
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Definitely, a little more information would go a long way towards letting us help you. What brand of seatpost is it? If you don't know, then a pic would be helpful.

Generally, check the torque recommendations from the seatpost mfgr and use a torque wrench to attain the right torque. I typically grease the threads before tightening, unless the mfgr specifically recommends not to. If it still loosens, get a thread locking compound such as loctite, vibratite or any of the other off brands that local hardware stores carry. If you do resort to thread locker, you should first thoroughly remove the grease that I just told you to put on.
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Old 10-28-10, 02:35 PM   #6
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If this is something that's been repeatedly re-tightened, the bolt-threads could be worn out. Replace the bolt(s) with new ones, use a little blue Loctite and torque it to the manufacturer's recommended setting. The seat-clamp bolts are typically 8mm and require A LOT of force, something around 20-25 lb*ft.
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Old 10-28-10, 02:58 PM   #7
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The seatpost uses the same style of clamp as Thompson though the post came with the bike and has no logo on it so it is likely not a Thompson.

The general consensus here seems to be that unless I grossly undertightened the bolts it would not be normal for the seat clamp bolts to just work loose. That's all the info I was looking for.
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Old 10-28-10, 03:03 PM   #8
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If it is a Thompson, or even a Thompson copy, you probably should NOT replace the bolts unless you get the identical ones from the maker of the seatpost. The Thompson bolts are not standard - the head is machined with a spherical seat to apply even tension from various angles. A standard bolt would be likely to fail prematurely.
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Old 10-28-10, 03:08 PM   #9
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OK .. less in the dark +1 on Loc Tite threadlock . the blue .

you might consider shimming around the saddle rails if that clamp is loose
and the bolts have bottomed out
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