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Old 04-16-14, 12:02 PM   #1
02Giant 
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To sleeve or not to sleeve, that is the question.

I am considering replacing my carbon seat post, one I have found is a smaller diameter, it is carbon. Is it OK to sleeve a carbon frame for a carbon seat post?
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Old 04-16-14, 12:12 PM   #2
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the aluminum accurately machined sizing shim should be fine ..

though I'm told 7000 series aluminum , because of its Zn content is not the best, in contact with carbon..

but 6000 series should be fine ..

have used several shim adaptations 25.0 seat posts in 27.0 & 27.2 frames

have shims around the 27.2 thudbuster seatposts in 2 bikes I use all the time, now ..
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Old 04-16-14, 12:14 PM   #3
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Sounds like you'll be ok if you:

1) Use the correct seatpost shim. Problem solvers sells many, and any LBS can order from their catalog.
2) Use carbon assembly paste
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Old 04-16-14, 12:14 PM   #4
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Yes, but there's the issue of galvanic corrosion where carbon and aluminum meet. Use an anti-seize and hopefully there'll be enough traction to hold. Otherwise you can use carbon assembly paste which offers more traction on both the inner and outer surfaces of the sleeve.

Lastly, the slot in the sleeve and seat tube have to line up so the clamp can work effectively. That means you'll have an open channel for war to enter the frame. I use a dab of silicone bathtub caulk to seal this, and even with a decent seal make sure I have an open weep hole in the BB shell of all my bikes.
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Old 04-16-14, 12:55 PM   #5
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This bike doesn't get ridden in the rain, not saying it couldn't get caught out if it started raining. Would there be any advantage to using a thermoplastic shim?
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Old 04-16-14, 01:00 PM   #6
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Yes, trying to imply, the C-Zn Al being more reactive than a C-Si Al alloy being 1 difference in the 2 alloy groups
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Old 04-16-14, 03:03 PM   #7
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i wouldn't involve any shim unless there was no other alternative, so i would search for a post of the right dimension. if all else fails, i wouldn't worry at all about a carbon post/alloy shim/carbon seattube combo.

if i understand it correctly, a galvanic reaction involves two dissimilar metals in contact and an electrolyte. there is only one metal and precious little electrolyte, but others will no doubt disagree.

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Old 04-16-14, 03:12 PM   #8
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Perhaps the epoxy of the composite is thick enough .
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Old 04-16-14, 03:17 PM   #9
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Originally Posted by hueyhoolihan View Post
i wouldn't involve any shim unless there was no other alternative, so i would search for a post of the right dimension. if all else fails, i wouldn't worry at all about a carbon post/alloy shim/carbon seattube combo.

if i understand it correctly, a galvanic reaction involves two dissimilar metals in contact and an electrolyte. there is only one metal and precious little electrolyte, but others will no doubt disagree.
Galvanvic reaction does not require two metals per se, just two substances of different electrolytic potential. Cabon qualifies just like in a low end dry cell battery.
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Old 04-16-14, 03:27 PM   #10
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Yes, but there's the issue of galvanic corrosion where carbon and aluminum meet. Use an anti-seize and hopefully there'll be enough traction to hold. Otherwise you can use carbon assembly paste which offers more traction on both the inner and outer surfaces of the sleeve.
Anti-seize prevents corrosion by way of a metal filler at lower potential than what you're protecting.

Most anti-seize is aluminum based; and while you get some protection from the grease excluding water there's nothing to sacrificially corrode instead of an alloy bike part. In fact, the zinc-based alloys used for structural purposes are at a lower potential and should oxidize preferentially to the pure aluminum in the anti-seize.

Zinc based anti-seize is intended for aluminum.
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Old 04-16-14, 07:26 PM   #11
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Thanks to all for the insight. I seen a seat post for sale on the forum I was considering, unfortunately I realized this afternoon as I was getting ready to head out and get a few miles in, I left my cycling shoes behind after Saturdays ride. So instead of replacing my stem and seat post, I will be buying new shoes. Crap like this almost makes me physically sick.
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Old 04-16-14, 07:42 PM   #12
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Thanks to all for the insight. I seen a seat post for sale on the forum I was considering, unfortunately I realized this afternoon as I was getting ready to head out and get a few miles in, I left my cycling shoes behind after Saturdays ride. So instead of replacing my stem and seat post, I will be buying new shoes. Crap like this almost makes me physically sick.
I'm sorry to hear that, but shoes? I've heard of helmets, and front wheels being lost this way, but shoes? Did you go home barefoot?

Sorry to give you some grief, which I hope you'll accept as good natured, but sometimes you have to laugh in the face of minor misfortune.
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Old 04-16-14, 07:51 PM   #13
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I'm sorry to hear that, but shoes? I've heard of helmets, and front wheels being lost this way, but shoes? Did you go home barefoot?

Sorry to give you some grief, which I hope you'll accept as good natured, but sometimes you have to laugh in the face of minor misfortune.
Taken as intended, I can't drive wearing them so I wear flip flops to and from the trail and switch. I took them off and intended to set them in the back of the truck with my bike, didn't realize they weren't there when I got home, had I noticed I may have been able to go back for them.

Live and learn, someone got a nice pair of cycling shoes.
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