Thomson post slips even with tacx

Discuss light weight issues concerning road bikes & parts.
Ufgators
Posts: 220
Joined: Sun Sep 27, 2009 4:28 pm

by Ufgators

I have a Parlee z0 fitted with the proper size Thomson masterpiece seat post and I notice that the post slips a
Couple millimeters per a 2 hour ride with 6nm of force on the clamp and a generous coat of carbon paste. Any suggestions? Thanks

by Weenie


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Devon
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Location: Oxford, England

by Devon

May be a silly question but are you 100% sure it's the right size post? Should be 31.6mm

Is the post/inside of the seat tube worn at all?

How much do you weigh?

A quick/easy temporary fix would be to wrap the inserted end of the post in a thin layer of electrical tape.
Campagnolo; because it's a bicycle, not a fishing rod.

Ufgators
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Joined: Sun Sep 27, 2009 4:28 pm

by Ufgators

alexh wrote:May be a silly question but are you 100% sure it's the right size post? Should be 31.6mm

Is the post/inside of the seat tube worn at all?

How much do you weigh?

A quick/easy temporary fix would be to wrap the inserted end of the post in a thin layer of electrical tape.


Just measured it with digital calipers. The post measure 31.6 millimeters so probably within tolerance. The post isn't worn and the frame is new.

Ufgators
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by Ufgators

I forgot to add I weight 155 pounds

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Devon
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by Devon

I see no reason why it should be slipping in that case, unless there is an issue with the clamp? Try some threadlock/a new bolt maybe?
Campagnolo; because it's a bicycle, not a fishing rod.

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MajorMantra
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by MajorMantra

Could be your torque wrench is out?

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Rick
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by Rick

There has to be something else going on here. There is nothing about a Thomson seatpost that should allow unusual slip.

Ufgators
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by Ufgators

Should I try more clamping force? Say 6.5nm?

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Devon
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by Devon

Ufgators wrote:Should I try more clamping force? Say 6.5nm?


I'd personally check the clamp first.
Campagnolo; because it's a bicycle, not a fishing rod.

Ufgators
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Joined: Sun Sep 27, 2009 4:28 pm

by Ufgators

alexh wrote:
Ufgators wrote:Should I try more clamping force? Say 6.5nm?


I'd personally check the clamp first.


What do I look for in defective clamp?

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Devon
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Location: Oxford, England

by Devon

Ufgators wrote:What do I look for in defective clamp?


Shearing of the bolt/nut, or the clamp may be slightly too large for the frame and therefore unable to provide suitable clamping force.
Last edited by Devon on Thu Jun 13, 2013 3:30 pm, edited 1 time in total.
Campagnolo; because it's a bicycle, not a fishing rod.

thisisatest
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by thisisatest

Grease between the clamp and frame. Grease bolt threads fully, and under the bolt head. As before, Tacx paste on post to frame.

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ghisallo2003
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Joined: Mon Jan 02, 2006 7:10 pm

by ghisallo2003

I have always found that the Masterpiece posts are marginally smaller than the normal posts from Thomson. I wonder if the extra machining takes a small amount from the overall diameter. I know it is not the principle of WW, but if the torque is correct and the clamp ok, I would try another Masterpiece to see if it is a case of upper-lower tolerances, and then think about a non-Masterpiece. The weight savings are modest compared to having a robust seat fitting.

1415chris
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Location: Surrey UK

by 1415chris

If the Masterpiece is not robust, nothing is robust :wink:

by Weenie


sungod
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by sungod

i had a similar problem with my ax europa post

6Nm, maximum rated torque - wrench checked against calibrated one at work
clamping bolt/nut threads clean and lubed
inside of seat tube degreased
the post is a tight fit

tacx paste didn't solve it - pink paste

finish line paste didn't solve it - white paste with gritty feel

but a mix of the two pastes did, at 6Nm the post no longer slips, been ok with this method for 3 years now

have to reapply paste mix any time i remove/refit the post, i.e. after boxing the bike for travel, otherwise it will slip without fail

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