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I'm just messing with you
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Discussion Starter #1
I'm looking for some advice/help on a slipping seat post. It has always been a problem on this bike. I've used both an American Classic, and a Thomson Elite (current), and both slip.

The seat tube has "ears" welded to it for a quick release fastener. Initially I thought the QR might be the problem, so at some point I threaded a heli-coil into one side and use a grade 8 bolt through the other, but it still slips.

I tighten it to the point that I'm afraid I'm either going to snap the bolt or worse. I noticed today that it's slipped again, so thought I'd ask for tips on what I could try next while it's on my mind.

FWIW - the first post I used was an AC, the slipping wore a flat spot on the post to where it won't stay where I need it at all. The current Thomson post may be worn the same way, but I haven't checked it. I have a spare Syncros stashed away in case the Thomson gets to the point of not being usable. I know it's slipping because I've got it marked with a white line - I raise the post up to where the line is 1/4" or so above the top of the seat tube, and eventually it'll end up inside the tube and out of sight. Then wash, rinse, repeat.

Any tips on what I could do to fix this situation is appreciated.
 

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defender of bad taste
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Are you hugely overweight or using the wrong size post? Having eliminated those possibilities have you tried roughing up the inserted portion of post with some glasspaper?
 

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Crawfishy
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I had this problem on a new frame and did some research on it. It is usually not the post but the frame. It can be hundreths of a mm off but it is a problem. The only was to tell is to use a set of digital calipers. I found a post on MTBR were some people recommended using a coke can shim or even natural chaulk. It tried both and had no luck.

I wasn't worried about the frame becoming something that will ever fit the VRC category so I used some Truck Bed Liner from a spray can to add some thickness to the seat tube. So far it has worked perfect.
 

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I'm just messing with you
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Discussion Starter #4
mechagouki said:
Are you hugely overweight or using the wrong size post? Having eliminated those possibilities have you tried roughing up the inserted portion of post with some glasspaper?
No, no, and no. Thomson posts are ridged, so they're sort of rough on their own.
 

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I'm just messing with you
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Discussion Starter #5
Crawfishy said:
It is usually not the post but the frame.
Since it's repeatable with two different posts, I'm pretty sure it's the frame.

The ears look like they squeeze together, but the slot doesn't. I'll try to get some close-ups tonight, I've got a headset to install so I'll be working on the bike anyway.
 

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I have a frame where a Thomson post also tends to slip. Although the Thompson is "rough," I'm not sure it's "rough enough."

Assuming that the post is the right size (31.8mm for a Phoenix), to make it stop slipping you need more friction between the post and frame to prevent it from sliding. Less grease on the post may do the trick. I've heard of people using chalk instead of grease. Or roughen the inside of the seat tube to create a surface with more friction. Unless, the seat tube has been reamed and is now over-sized requiring a slightly larger post, the answer is "more friction."
 

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laffeaux said:
I have a frame where a Thomson post also tends to slip. Although the Thompson is "rough," I'm not sure it's "rough enough."

Assuming that the post is the right size (31.8mm for a Phoenix), to make it stop slipping you need more friction between the post and frame to prevent it from sliding. Less grease on the post may do the trick. I've heard of people using chalk instead of grease. Or roughen the inside of the seat tube to create a surface with more friction. Unless, the seat tube has been reamed and is now over-sized requiring a slightly larger post, the answer is "more friction."

Pretty sure they take a 31.6.

For friction you can use dirt (may not be the best option :)), toothpaste, or a grease made specifically made to increase friction for slipping carbon seatposts.
 

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IVMTB & VMBEFG Illuminati
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i have the same exact issue with my Phoenix so you're not alone. i feel that the frame is too large for the 31.8mm. a 31.9 would probably be perfect.

grease in binding situations can actually help hold things together. i've seen slipping handlbars on BMX bikes corrected with a liberal amount of grease. i personally wouldn't remove the grease without having something else in there that would prevent rust. beyond that i don't have a solution for you. i have not begun the task of working on my Phoenix to correct the problem.
 

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Master of the Face Plant
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Veloculture said:
i have the same exact issue with my Phoenix so you're not alone. i feel that the frame is too large for the 31.8mm. a 31.9 would probably be perfect.

grease in binding situations can actually help hold things together. i've seen slipping handlbars on BMX bikes corrected with a liberal amount of grease. i personally wouldn't remove the grease without having something else in there that would prevent rust. beyond that i don't have a solution for you. i have not begun the task of working on my Phoenix to correct the problem.
I had exactly the same problem. I found that using a really thick grease helped. Beyond that I actually greased the post and then sprinkled a little sand from the kids sandbox on the grease. It never slipped again. I know it is a little nuts but it worked.
 

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- Beer can shim

- Run an undersize post like a 27 or 27.2 and use a 'problem solvers' type seat post specific shim.. maybe knurl the outside of the shim first to take up some space.

- Knurl your current post (either hand knurl ie punch marks, or a good shop will have either a lathe or the Stein knurling tool).

-See if you can find a 31.9 post.. maybe that would work. Use a flex hone on a drill if you need more space

-Take it to a frame builder and either get it taken up to the next size, and/or have the ears taken off, as they provide very uneven clamping force as compared to a collar like a Salsa with a barrel nut.

- Use grease with sand in it.. like really fine blasting sand, or get some play ground sand and sift it.

- Get really into trials.

-Schmitty-
 

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Fan of 'Hams
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Schmitty said:
-Take it to a frame builder and either get it taken up to the next size, and/or have the ears taken off, as they provide very uneven clamping force as compared to a collar like a Salsa with a barrel nut.
-Schmitty-
I have a Phoenix in with Steve now getting "re-Eared" as its prior owner thought that might be the answer too... I don't think it was. I'd try everything else on the response list here and then still think long and hard before taking a hacksaw (or line-borer) to something as collectible/valuable as a Phoenix.
 

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halaburt said:
I have a Phoenix in with Steve now getting "re-Eared" as its prior owner thought that might be the answer too... I don't think it was. I'd try everything else on the response list here and then still think long and hard before taking a hacksaw (or line-borer) to something as collectible/valuable as a Phoenix.

Not advocating a hack job. Use your own discretion... if it's *that* collectible to someone, maybe it should just be retired, and then the post is a non issue....


-Schmitty-
 

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I recognise the problem too with my Phoenix. After many years of hard service, my seatpost slips a little too. I found an easy solution. I bought a 31.8 Salsa liplock-collar and clamped this around the seatpost (shaving down a little to get it fitt even around the seatpost). This collar stops the seatpost from sinking further. Of course it also makes lowering the seatpost less fast, but this is a nonissue for me. Probably not the most elegant solution, but works perfect.
 

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I'm just messing with you
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Discussion Starter #19
It's good to know I'm not alone. The frame has had this problem from day one. I didn't buy it new, but it had never been built when I got it.

I have read before about the friction paste mentioned above, and seem to remember you can end up with the post stuck. That memory may be false though, but there was some downside that kept me from trying it.

I'm definitely the right sized 31.8 post, and again, with two posts slipping, it's gotta be the frame at fault. Hanging it on the wall is not an option.

I blame the ears, but I'm not going to hack them off. Collectible or not, that just doesn't seem to be a good idea.

When I put the post back in (had it out to drain a wee bit of water), I carefully tightened the bolt to where the two ears came flush together, so maybe that will do it, maybe not.

I like Pottser's idea - has the lip lock messed up the top of the seat tube any?
 

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wv_bob said:
has the lip lock messed up the top of the seat tube any?
It'd be easy enough to make a platsuc/rubber washer to go in between. make sure not to damage the post.

You could also file some material from the inside of the 'ears', but this will only treat the symptom, and may actually make it worse by allowing you to tighten more. That style binder actually pushes inward -very unevenly- at the ears.. worst case you can actually dent the post.

The knurling and beer can shim ideas are the best,and least obtrusive imo.

-Schmitty-
 
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