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Dropper post and seat post collar problem

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Dropper post and seat post collar problem

Old 08-04-20, 11:51 PM
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TiHabanero
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Dropper post and seat post collar problem

Have an unusual one here. 2020 Giant Trance carbon frame with a two bolt seat post collar (seat post clamp) and the stock Giant dropper post. If both seat post collar clamp bolts are torqued to spec at 5nm the dropper post goes down, albeit with some effort, but won't come back up. If both bolts are torqued to 4nm the post goes down in the same manner, and comes back up, but not all the way back up. Falls about 1cm short of full extension. If only the bottom bolt on the seat collar is torqued to 5nm and the top bolt torqued to 1 or 2 nm then the post works perfectly. This started happening after the customer lowered the post in the frame.
My thoughts on this is the top edge of the seat post collar is putting excessive pressure in a localized area on the post when torqued to 5nm and deforming it enough to cause the problem. Does this sound reasonable?
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Old 08-05-20, 03:51 AM
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trailangel
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Hmm. Can't see the 2 bolt clamp, but is one of them a bolt for tightening a shim because the post is not the same diameter as the seat tube?
If it started happening after customer pushed the seatpost lower, I'd raise it back up and try it. Maybe it's too low and binding down in the seat tube, or if internal dropper the cable end is messed up or hitting something down in the tube.
They do say not to over tighten, but has to be tight enough.
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Old 08-05-20, 07:10 AM
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aggiegrads
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Does the clamp have a lip that is wider than the thickness of the seat tube? That could put pressure on a very thin ring directly on the post. Not likely with a carbon frame, but worth a measure.
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Old 08-06-20, 04:08 AM
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TiHabanero
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aggiegrads, that was my thought as well, and will be taking some measurements on Friday. Meanwhile I am waiting to hear from Giant. This covid thing has increased response time with the company. Ain't nothing easy in this world.
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