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2021 Domane gen3 - seatmast/seatpost slipping

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2021 Domane gen3 - seatmast/seatpost slipping

Old 02-09-24, 07:22 PM
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2021 Domane gen3 - seatmast/seatpost slipping

I have an issue with a gen3 domane, the seatmast slips to the bottom, tightness of the nut doesn't matter. I've read there is a service bulletin about it, but i built this up from a frame, so I no easy access. Anyone have the actual service bulletin talking about correcting this. I believe it involves sanding some paint on the inside that was too smooth allowing the mast to move.

Already tried carbon grit paste (or whatever the name is) and no luck. Now I have to figure out how to get the mast up enough to undo the hex nut. ugh.
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Old 02-09-24, 09:10 PM
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I do not ever remember the Gen 3 having that issue, I know the Gen 4 had that issue. You will probably need to call a Trek shop and ask them as I am not sure they post that stuff online
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Old 02-09-24, 11:11 PM
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gen4 has a similar issue in effect, if completely different in mechanism. The fun part on the 3 is that its all internal, so if it slips down the only way to remove the pressure is to unscrew it from the back through a slot. The mast can go far enough to block you from unscrewing.

There are a bunch of references to the issue on different sites and a reference to "fix" from trek.

I will try to stop at the trek dealer tomorrow, but they go through mechanics left and right. hopefully they have someone who actually knows. I just hate taking their time to be honest. \
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Old 02-10-24, 05:33 AM
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Yeah they donít post (no pun intended) these things online. The fixes to the Madone 2019 seatpost slipping was an open secret between Trek and LBSes (cut off the washers on the bolts) and they issued an advisory about the Isospeed seatpost loosening horizontally which only went to dealers.
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Old 02-10-24, 07:09 AM
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Had the same thing happen to my gen3. Local shop went back and fourth with different Trek recommended fixes. Carbon paste, slight over torque, replaced post. Would still slip down. Sometimes subtle so I would mark the bolt location.
Trek just swapped the frame for a gen4. Haven't ridden it yet because NE WEATHER.
BRING TO YOUR SHOP. Have them contact Trek. And repeat until everything tried.
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Old 02-10-24, 07:01 PM
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This is a NOS frame and not purchased directly through my local dealer. Understanding that, I may not be able to get warranty or trek direct assistance and need actual help on how to solve.

I was unable to get over there today, will try again next week, but again they will not help for free and would rather find the solution outside of going there.
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Old 02-10-24, 08:23 PM
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Even over tightening the allen bolt will not push enough to wedge the block tight enough. Creating a steel "bevel" washer that was just thick enough to cup the ball (after cleaning everything inside) with some carbon paste is one way to go at it. Another is to put heat shrink around the other "flat" piece & trim it so the screw holes are exposed is another possible method.

Have you tried an entirely new seat post with new hardware? How far is the seat post going into the seat tube?

To get the seat back up in order to bring the allen bolt back in view will require some blunt hits from a hefty dead blow... put an expendable seat on prior to using the dead blow. The frame will need to be held firmly in place, as any give will reduce the impact effectivity.
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Old 02-10-24, 08:49 PM
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Tough situation if no warrantee help.
What shop owner/mechanic and I hypothesized was the internal seat tube was wider at the lower points,but narrower up near top. So if it slipped just a drop, you lost your torque, and it slipped further. For us, with trek guiding us, a replacement post and carbon paste didn't help.
They didn't suggest wrapping anything around the wedge, but that is what I would have tried, maybe some kind of rubber or shrink wrap.
You didn't get this from a trek dealer? Even if it was leftovers, original owners should get frame warrantee.
I wish you luck.
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Old 02-10-24, 09:15 PM
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I had the problem with my Gen 3 SL6. Paste and the wedge mechanism must be clean and well lubed to reduce friction in it so the torque provides the pressure. Paste alone did not work. I did have to use a rubber hammer to re expose the bolt once.
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Old 02-10-24, 10:32 PM
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Originally Posted by Troul
...Have you tried an entirely new seat post ...
Originally Posted by scot
This is a NOS frame and not purchased directly through my local dealer. Understanding that, I may not be able to get warranty or trek direct assistance and need actual help on how to solve.
I was unable to get over there today, will try again next week, but again they will not help for free and would rather find the solution outside of going there.

I know it is slightly different with the Domane Gen 3, but I had an issue with the Bontrager RSL seatpost on my CheckPoint slipping, worked perfectly fine in 2 other bikes, but would slip in my CheckPoint. Discovered that right where I needed to position the post in my CheckPoint, the post was undersized, sized out to 27.02 versus the 27.2. It was really odd and stumped me initially, until I decided to check the post sizing. I also check the CheckPoint using the post out of my Emonda, also running a Bontrager RSL and it did not slip, so that ruled out the frame being wonky. Trek warrantied my seat post and all has been good since. So could be worth checking the post sizing just on the off chance. I'd never had that issue before, so it was really the last thing I even thought about.
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Old 02-11-24, 12:11 PM
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Originally Posted by Troul
Even over tightening the allen bolt will not push enough to wedge the block tight enough. Creating a steel "bevel" washer that was just thick enough to cup the ball (after cleaning everything inside) with some carbon paste is one way to go at it. Another is to put heat shrink around the other "flat" piece & trim it so the screw holes are exposed is another possible method.

Have you tried an entirely new seat post with new hardware? How far is the seat post going into the seat tube?

To get the seat back up in order to bring the allen bolt back in view will require some blunt hits from a hefty dead blow... put an expendable seat on prior to using the dead blow. The frame will need to be held firmly in place, as any give will reduce the impact effectivity.
Could you describe your suggestions a bit more. I get the idea of the cup and ball setup as Iíve disassembled the post but I donít know what you are suggesting. A bevel washer?

Then you state heat shrink around the flat piece. The rear face of the seat post is flat. The back of the bevel ďballĒ is flat. But not sure what you are describing.
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Old 02-11-24, 12:17 PM
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Originally Posted by biker128pedal
I had the problem with my Gen 3 SL6. Paste and the wedge mechanism must be clean and well lubed to reduce friction in it so the torque provides the pressure. Paste alone did not work. I did have to use a rubber hammer to re expose the bolt once.

Mine is UBER clean now. Disassembled and used iso alcohol to clean annd degrease everything. Also cleaned in the mast.

Then reinstalled and it still slipped.

Where are you putting grip paste? Iíve read a few lines talking about not putting it on the wedge face, only putting it on the contact side (flat with ridges) which makes sense to me, but not sure.

Iím a bit worried about greasing the screw etc as that would change the effective torque through to the wedge.
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Old 02-11-24, 06:56 PM
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Originally Posted by scot
Mine is UBER clean now. Disassembled and used iso alcohol to clean annd degrease everything. Also cleaned in the mast.

Then reinstalled and it still slipped.

Where are you putting grip paste? Iíve read a few lines talking about not putting it on the wedge face, only putting it on the contact side (flat with ridges) which makes sense to me, but not sure.

Iím a bit worried about greasing the screw etc as that would change the effective torque through to the wedge.
I tried the same thing. Clean metal to metal does not slide as well. Just a little bit of grease on the threads and washer and spherical part. Reduced metal to metal friction and I did not have to over torque the bolt.
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Old 02-12-24, 01:39 PM
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Forgot to answer the question on the paste. I put it on the wedge and the post. Holds well. I rode (not raced) a cyclocross CAT 5 race in December and yesterday road the short course of the Pantani Gravel ride. Bumps have not moved it. I also have a long post I use in the the bike stand for maintenance and short post for the seat. So the psot comes out every month. I have cleaned and reapplied the paste in a year.

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Old 02-13-24, 06:38 PM
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Originally Posted by biker128pedal
I road (not raved) a cyclocross CAT 5 race in Decembe
rode?
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Old 02-14-24, 07:18 AM
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Turns out it was the brand new seat mast, we found another to check it against and no slipping. Trek is replacing under warranty, but my guess is the cup and ball are not made right as it otherwise felt like it should have been all good. Not sure, but should be able to give a final update EOW when a new one comes in.
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Old 02-19-24, 10:13 AM
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And... no. The new seatpost came in, they said it didn't slip. My work week was too much and didnt get a chance to get outside until yesterday. Slipped when tightened to spec at my proper height.

I'm still out of options and not sure what to do. So frustrated.
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Old 02-20-24, 09:25 AM
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Originally Posted by scot
And... no. The new seatpost came in, they said it didn't slip. My work week was too much and didnt get a chance to get outside until yesterday. Slipped when tightened to spec at my proper height.

I'm still out of options and not sure what to do. So frustrated.
carbon paste and tighten it a bit more, I reckon
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Old 02-22-24, 06:11 PM
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Trek forbids paste and over torquing, 7nm and dry only. Trek (company) is working on a solution.
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Old 02-23-24, 06:02 AM
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Originally Posted by scot
Trek forbids paste and over torquing, 7nm and dry only. Trek (company) is working on a solution.
Well they recommended that on my Madone (not by much). I think they solved the issue on the 2022 design.

Maybe the Domane is different.

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Old 02-23-24, 06:37 AM
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Originally Posted by scot
Trek forbids paste and over torquing, 7nm and dry only. Trek (company) is working on a solution.
They did on mine too. Then frame was replaced.
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