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BMC Owners . . . any solution for the dreaded seatpost slippage?

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BMC Owners . . . any solution for the dreaded seatpost slippage?

Old 11-04-18, 07:28 PM
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BMC Owners . . . any solution for the dreaded seatpost slippage?

I'm a long-time BMC rider but I've come across a problem that apparently defies solution. If you've bought a BMC TeamMachine or RoadMachine over the past two or three years, you're familiar with the slick looking "no gap" (concealed) seatpost clamp. I had an early production 2018 BMC SLR01 and neither I nor my LBS could ever get the seatpost to stop slipping. We worked on it for months. We put assembly paste all the way around the seatpost (contrary to instructions, lest it freeze the post permanently), we over-torqued the clamp to nearly twice its value and eventually, after nine months of trying various unsuccessful cures, the clamp pulled through the frame. To be fair, we occasionally were able to get the post to stop slipping for a month or six weeks, but the slippage always returned. BMC warrantee'd the frame and my LBS set me up with a 2019 BMC SLR01 frameset as a replacement.


Now . . . I've put all of 300 miles on the 2019 frameset and . . you guessed it . . . the seatpost is slipping down. When my LBS assembled the new bike, he put assembly paste all the way around the post, but to no avail. I feel as if we've tried EVERYTHING to get the BMC seat clamp to work, but nothing has worked for very long. This is otherwise a GREAT bike, so here are my questions. Maybe somebody out there has found a fix that we don't know about . . .


If you have a BMC with the "no gap" concealed seat post clamp, did you also have the seatpost slippage problem?


If you did, were you able to find a fix? Were you able to retrofit an exposed seatpost clamp? Is the problem the clamp or is it the seatpost (or is it both)?
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Old 11-05-18, 05:50 AM
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Epoxy.
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Old 11-05-18, 06:07 AM
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What is your weight OP?
A suggestion...use carbon paste of course...is you need to abraid the clear coat of the post were it sticks inside the frame.
Take #600 grit wet sandpaper, mark the post with painters tape for depth of penetration and likely take a couple thou off the carbon gel coat on the post.
Likewise do the same for the interior of the seat tube which typically is less critical because it doesn't have the same paint/clearcoat coverage.

That, plus carbon paste, torque to spec with a torque wrench and you should be good.

If you have bad build tolerance between post and seat tube ID with carbon I would be loathe to introduce a stress riser to mitigate slippage...a small shim because this can load the carbon creating high stress.
Can you post a pic of the seatpost...and/or tell us if it is proprietary...or generic 27.2mm round post for that particular model BMC?
If you can't resolve it with the above method and the bike uses a proprietary seatpost, I would sell the frame and ride something else.
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Old 11-05-18, 06:12 AM
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Originally Posted by Kimmo View Post
Epoxy.
I've thought of that. Epoxy would make it hard to service the Di2 battery, though.
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Old 11-05-18, 06:19 AM
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Originally Posted by Campag4life View Post
What is your weight OP?
A suggestion...use carbon paste of course...is you need to abraid the clear coat of the post were it sticks inside the frame.
Take #600 grit wet sandpaper, mark the post with painters tape for depth of penetration and likely take a couple thou off the carbon gel coat on the post.
Likewise do the same for the interior of the seat tube which typically is less critical because it doesn't have the same paint/clearcoat coverage.

That, plus carbon paste, torque to spec with a torque wrench and you should be good.

If you have bad build tolerance between post and seat tube ID with carbon I would be loathe to introduce a stress riser to mitigate slippage...a small shim because this can load the carbon creating high stress.
Can you post a pic of the seatpost...and/or tell us if it is proprietary...or generic 27.2mm round post for that particular model BMC?
If you can't resolve it with the above method and the bike uses a proprietary seatpost, I would sell the frame and ride something else.
I weigh 175 lbs. And the BMC seatpost is proprietary and it is textured from the factory. The cross section of the tube is "D" shaped, so there is no off-the-shelf substitute.

I guess my original post wasn't as clear as it should have been. Of course, we've done carbon paste -- even in areas BMC says not to use carbon paste (lest it seize the post permanently). And we've torqued to spec. We've even torqued to double spec. Didn't work for long. The inside of the tube and the outside of the post are textured already -- but that's not to say the texturing is sufficient. It apparently isn't. But I don't think sanding down the texture is going to help.

Thanks for the ideas.
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Old 11-05-18, 06:29 AM
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Put cling wrap into and over the seat tube, apply epoxy to the post so it forms a ledge against the top of the seat tube.
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Old 11-05-18, 06:30 AM
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I had the same problem with a Cervello R3 carbon seat post and this solved my problem:

KCNC SC13 Twin Seat Post Clamp


KCNC's Twin Clamp is designed to solve the annoying slipping seat post! It does happen - and this clamp is designed to prevent posts slipping down inside the frame by having 2 clamps joined together - one clamps the seat tube as normal but the top clamp grips the seat post itself to provide an extra clamping force without over stressing the seat tube clamp or the seat tube and seat post itself!

https://www.sjscycles.co.uk/seat-pos...clamp/?geoc=US
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Old 11-05-18, 07:07 AM
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Originally Posted by joesch View Post
I had the same problem with a Cervello R3 carbon seat post and this solved my problem:

KCNC SC13 Twin Seat Post Clamp


KCNC's Twin Clamp is designed to solve the annoying slipping seat post! It does happen - and this clamp is designed to prevent posts slipping down inside the frame by having 2 clamps joined together - one clamps the seat tube as normal but the top clamp grips the seat post itself to provide an extra clamping force without over stressing the seat tube clamp or the seat tube and seat post itself!

https://www.sjscycles.co.uk/seat-pos...clamp/?geoc=US
That looks like a good solution for round seatposts. Unfortunately, the BMC seatpost is "D" shaped.
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Old 11-05-18, 08:18 AM
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Originally Posted by FlashBazbo View Post
That looks like a good solution for round seatposts. Unfortunately, the BMC seatpost is "D" shaped.
Should be easy enough to make one to fit. Contact me offline if you are interested in pursuing something like that. If the problem is common enough I am more than willing to invest some time into finding a proper solution.
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Old 11-05-18, 08:23 AM
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I have the same bike (Teammachine SLR01) and had seatpost slippage after the first couple of rides. I talked to my LBS and they said to torque the bolt tighter. I also applied more carbon paste, but only on the areas BMC recommends. That plus the more torque (it was less than double the recommended spec) and I haven't had a problem. On all my bikes I apply a little paint to the seat post just above the collar to make it easy to visually check if there's been any slippage. FWIW, I weight 140 pounds so the fact that it slipped on me originally using the recommended torque specs shows there is a problem with the seatpost and/or collar design.
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Old 11-05-18, 08:47 AM
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Originally Posted by FlashBazbo View Post
I weigh 175 lbs. And the BMC seatpost is proprietary and it is textured from the factory. The cross section of the tube is "D" shaped, so there is no off-the-shelf substitute.

I guess my original post wasn't as clear as it should have been. Of course, we've done carbon paste -- even in areas BMC says not to use carbon paste (lest it seize the post permanently). And we've torqued to spec. We've even torqued to double spec. Didn't work for long. The inside of the tube and the outside of the post are textured already -- but that's not to say the texturing is sufficient. It apparently isn't. But I don't think sanding down the texture is going to help.

Thanks for the ideas.
Just so you know, texturing isn't the same as high coef. of static or dynamic friction. Since you have tried all the correct things to keep the post from slipping, your next step would be to do as I suggest and abrade i.e. remove the surface finish over the texture to increase 'bite' of the post at the clamp area. If the textured area of the clamp has a common protective carbon gel (clear) cost it is inherently slippery in spite of texturing. I hope that makes sense.
If you want greater clarity, post close up pictures of the seatpost and interior of the seat tube with the post removed exposing the clamping area.
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Old 11-05-18, 10:38 AM
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Originally Posted by ttusomeone View Post
I have the same bike (Teammachine SLR01) and had seatpost slippage after the first couple of rides. I talked to my LBS and they said to torque the bolt tighter. I also applied more carbon paste, but only on the areas BMC recommends. That plus the more torque (it was less than double the recommended spec) and I haven't had a problem. On all my bikes I apply a little paint to the seat post just above the collar to make it easy to visually check if there's been any slippage. FWIW, I weight 140 pounds so the fact that it slipped on me originally using the recommended torque specs shows there is a problem with the seatpost and/or collar design.
Did you get yours at MOAB? (Mark is the one working with me on mine.)
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Old 11-05-18, 10:53 AM
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Originally Posted by FlashBazbo View Post
Did you get yours at MOAB? (Mark is the one working with me on mine.)
Yes, I got it at Moab, but the one in Franklin. Jeremy is the one that gave me the go ahead to make it tighter.
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Old 11-05-18, 01:04 PM
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No firsthand knowledge of this issue but given that it has no gap, it would follow that it has less allowable travel. That might indicate that it requires a very tight tolerance on the seatpost diameter dimensions. Since you are now on your second frame perhaps the seatpost is undersized preventing you from getting proper clamping force.

Since it's a proprietary seatpost, you'd probably have to get dims from BMC along with allowable tolerances to verify its within spec. Hopefully your dealer can do this for you. If not, maybe try and swap seatposts with another bike at the shop just to see if you can get it tight.
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Old 11-05-18, 01:23 PM
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Not a proper fix but - have you considered a clamp around the post just above the seattube so the post cannot slip down? I'm envisioning perhaps a wrap if innertube around the post that also covers the top of the seatpost, then a pipe clamp or seat clamp around the post. Not having your bike in hand and not being a CF guy, I cannot give you any details on how to do this but it seems to me that done right, it should work.

Ben
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Old 11-05-18, 01:40 PM
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Originally Posted by Campag4life View Post
What is your weight OP?
A suggestion...use carbon paste of course...is you need to abraid the clear coat of the post were it sticks inside the frame.
Take #600 grit wet sandpaper, mark the post with painters tape for depth of penetration and likely take a couple thou off the carbon gel coat on the post.
Likewise do the same for the interior of the seat tube which typically is less critical because it doesn't have the same paint/clearcoat coverage.

That, plus carbon paste, torque to spec with a torque wrench and you should be good.
I would actually go with something rougher, to really give the surface some tooth, and also on the face of the clamp itself, where it bears against the post. Doing this could vastly increase the friction when combined with a really rough carbon gel like Park's. (I have scratches in my clear coat on my bars from that Parks carbon paste/gel just from sliding it around during adjustment with the clamp loosened.)
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Old 11-05-18, 04:17 PM
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I had a similar problem with the Cervelo S3 seatpost which is airfoil shaped. Being a mechanical engineer, the slippage bugged me a lot. The solution was two steps: clean, lube, and retap the threads on the clamp to make sure the proper torque is applied to the screw. The second is to apply assembly paste only where the grip is needed. The surface between the clamping wedge and seatpost must slide to work, even to the point where you could lubricate the wedge. So I applied the carbon paste on the rear/sides of the post, and none on the surface of the wedge or front of the post. That worked.
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Old 11-05-18, 06:37 PM
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If there is enough clearance I would stick a strip of sandpaper (say, 180 grit wet& dry) to the seat post with some contact glue.
Rough side out.
On the side of the post that gets forced against the frame with the clamp.
If it doesn't work you could remove it as contact glue isn't too strong, then try another solution.
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Old 11-06-18, 06:25 AM
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Originally Posted by Dean V View Post
If there is enough clearance I would stick a strip of sandpaper (say, 180 grit wet& dry) to the seat post with some contact glue.
Rough side out.
On the side of the post that gets forced against the frame with the clamp.
If it doesn't work you could remove it as contact glue isn't too strong, then try another solution.
I wouldn't. Likely isn't doable because of lack of clearance between post and seat tube ID. Wouldn't do it anyway.
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Old 11-06-18, 06:29 AM
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Originally Posted by Wheever View Post
I would actually go with something rougher, to really give the surface some tooth, and also on the face of the clamp itself, where it bears against the post. Doing this could vastly increase the friction when combined with a really rough carbon gel like Park's. (I have scratches in my clear coat on my bars from that Parks carbon paste/gel just from sliding it around during adjustment with the clamp loosened.)
But not where to start IMO. Never begin more invasive with greater abrasion to the seat post IMO. Gel coat is slippery. Cutting the surface with 600# in my experience has been all that's necessary to create tooth and bite. Removing the gloss coat surface fractionally is all that is necessary...don't have to remove more material with rougher sand paper.
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Old 11-06-18, 08:26 AM
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Originally Posted by Campag4life View Post
But not where to start IMO. Never begin more invasive with greater abrasion to the seat post IMO. Gel coat is slippery. Cutting the surface with 600# in my experience has been all that's necessary to create tooth and bite. Removing the gloss coat surface fractionally is all that is necessary...don't have to remove more material with rougher sand paper.
I take your point, I was thinking less about removing more material than creating deeper scratches. Ie less sanding with rougher sandpaper. Just scuff it up real good. And also the clamp face.

This reminds me of the issues I had with the trek one-bolt seat mast topper. Could not get it to stop slipping. Finally took some 200 grit to both surfaces, and added in that park's carbon gel. (None of this is recommended by trek, obviously) granted, the parts I was scuffing were aluminum, but I was thinking the same principle could apply.
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Old 11-07-18, 07:12 PM
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UPDATE: My LBS received additional information. The theory is that the problem is NOT with lack of abrasiveness, but with lack of lube! BMC's instructions say to use carbon paste on 3 sides of the post but to lube the clamping wedge and the wedge side of the post (counter-intuitive at least at first). The idea is that, if the wedge doesn't slide freely, it binds during the torqueing process. (It tightens at an upward angle to the post.) You torque it to 5 Nm but after a little riding and jarring and shaking, the wedge comes "unbound" and the bolt loses some of its torque. The instructions, then, are to follow the instructions on paste and lube, torque the clamp to value, then do your best to rip the post out of the bike -- crank the nose of the saddle both directions, flex the post back and forth, ride the bike and bounce on the saddle -- really man-handle it -- then check the torque value. If the bolt remains at 5 Nm, all is well. If it drops, you've got to retorque and repeat the process of abusing the seatpost all over again.

Torque value is 5 Nm. First time we went through the routine, the torque value had loosened to 3 Nm. We repeated. The torque dropped again. We repeated and repeated and repeated . . . 8 times. FINALLY, after all the abuse, the torque value stayed at 5 Nm after each of the last three rounds. From here forward, I plan to check the torque on that bolt on a weekly basis. Hopefully, this was the solution. Time will tell.
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Old 11-07-18, 07:53 PM
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Different carbon paste brands have different granularities. Use the most course you can find, and if that isn't enough, put some sand in it, or micro glass beads.
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Old 11-08-18, 04:13 PM
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This thread reminds me of the old Notorious BIG song “Mo Money, Mo Problems.”
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Old 11-09-18, 03:50 AM
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Originally Posted by FlashBazbo View Post
UPDATE: My LBS received additional information. The theory is that the problem is NOT with lack of abrasiveness, but with lack of lube! BMC's instructions say to use carbon paste on 3 sides of the post but to lube the clamping wedge and the wedge side of the post (counter-intuitive at least at first). The idea is that, if the wedge doesn't slide freely, it binds during the torqueing process. (It tightens at an upward angle to the post.) You torque it to 5 Nm but after a little riding and jarring and shaking, the wedge comes "unbound" and the bolt loses some of its torque. The instructions, then, are to follow the instructions on paste and lube, torque the clamp to value, then do your best to rip the post out of the bike -- crank the nose of the saddle both directions, flex the post back and forth, ride the bike and bounce on the saddle -- really man-handle it -- then check the torque value. If the bolt remains at 5 Nm, all is well. If it drops, you've got to retorque and repeat the process of abusing the seatpost all over again.

Torque value is 5 Nm. First time we went through the routine, the torque value had loosened to 3 Nm. We repeated. The torque dropped again. We repeated and repeated and repeated . . . 8 times. FINALLY, after all the abuse, the torque value stayed at 5 Nm after each of the last three rounds. From here forward, I plan to check the torque on that bolt on a weekly basis. Hopefully, this was the solution. Time will tell.
FB, I know you are a pretty sharp guy and you are stuck with this bike...oh I am sure its a nice bike...BMC makes good road bikes. But the engineers that created that albatross should be taken behind the woodshed and horse whipped. What a bunch of a-holes. I am an engineer btw. When an engineer creates a design like this, they know 'all of the nuances' What you describe which btw, makes perfect sense should NEVER have been created. Grounds for selling the bike and never buying another BMC product. That is really f-ed up. Adjusting seat height, have the saddle stay in place, torque to a target torque of 5 Nm and it staying there should be intrinsic to the design. Whatta PITA. Just had to vent feeling your frustration. Designs get out there that are total BS and this is one of them.
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